Paccar MX v. Mercedes

April 18, 2011

Is the Paccar MX engine the Mercedes engine of the Peterbilt and Kenworth world?

Mercedes bragged about its engines great fuel economy, ease of maintenance, while still maintaining power to do the job. Paccar MX touts almost identical traits.

Now I have never personally drove the Paccar MX engine, however I have owned the Mercedes engine in 2 separate trucks, a Western Star and a Freightliner.

As far as the Mercedes engines go, the easiest word to sum them up is junk. These gutless wonders are lucky to pull their own weight up a hill much less the weight of a truck that is loaded with 40,000 lbs.

Granted they are light weight engines, and I will say I got average fuel mileage with it. But no different than I was getting with the Series 60 I had prior to it.

The Mercedes sat lower in the chassis and you could literally tear the engine down to the block in a 8 hours easy. So ease of maintenance was indeed a fact. Now the nice thing about that is for the mechanic, and you will get to visit him a lot once the engine gets a few hundred thousand on it. Once my engine warranty expired I started blowing head gaskets on a regular basis. Nice thing they are separate heads for each cylinder.

As far as power, let me see, how to compare. With my CAT and a 79000+ gross weight I can climb the hills in the flint hills of KS across I-70 at 50+ mph. Now bear in mind I usually set my cruise at 63-65.

In the Mercedes running about the same cruise speed I generally had to drop 2 gears and climb those hills at an average speed of 40 mph. and couple of them even a little slower, with the same weight.

Okay, okay granted kitty don’t get 6.5 mpg average like pukey did, but I needed longer to make the run. Now in Kitty’s defense, she is only averaging .2 mpg less; small trade for the performance difference. And I am pretty sure if I put a wing on top I can make that up.

Now as I stated I have not driven the new Paccar MX engine. HOWEVER!!! I have talked to a few guys that are running these newly touted angels of the Class 8 market. Now keep in mind that one mechanic I chatted with in regards to these engines stated they are equivalent of a C13 CAT.

These wonders are supposedly rated at 380 to 485 HP and up to 1750 torque; which is about the same torque as the older “E” class CATS had. They claim meeting all 2010 emission standards while having power and economy.


Now again as I have stated I have not driven one personally, so I cannot honestly attest to the accuracy of this information, however I would like to get my hands on one to make a battery run with it and see what it does with the weight.

From what I have been told by others driving this engine, one guy had a 2011 389 Peterbilt, another had a 2011 386, and I believe the last guy I talked to had a 389 as well but it didn’t look as long so perhaps it was a 388.

However all had the Paccar engine, all were at the shop for the same reason, Emission system problems.

I’m not sure the transmission setup in all the trucks just the first guy’s 389 had a 13 in it.

According to what all of them stated the Paccar engine is another gutless wonder. They claim going across 70 in KS and MO that it was nothing uncommon to drop 4 gears with 35,000 in the back. Now based on my calculations that equates to about 71,000 gross weight. Okay, so 8,500 lbs less and they are climbing the hills at 40 mph?  What is wrong with that picture? Sounds like Paccar put a Mercedes engine in the trucks.

In addition they claim an average fuel economy of about 4.7 mpg, not just 1 but all 3 of them. At least the Mercedes got some fuel mileage with no balls.

Again I state I haven’t driven one of these engines and I tend to be very frugal as far as fuel goes, so perhaps the touted economy is achievable, and these guys are just running as fast as they can legally go. Idling a lot and drag racing from stop lights, I can’t say.

I have found very few people who actually drive as I do, and it takes a lot of discipline to do so. I know it took me forever to teach myself to be light on the peddle, and it’s not a easy task with today’s traffic. But it pays in the end.

So anyone else have the Paccar MX engine? Is it really as bad as these guys make it out to be?

{ 35 comments… read them below or add one }

bob toomey August 20, 2011 at 8:35 pm

Had one 6 months now. It pulls decent and I am getting 7 mpg grossing 70,000 all the time. However, it has been in the shop 11 times with emission/computer related problems that the dealership cannot seem to fix. I try to give everything the benefit of the doubt, but if the majority are like mine, this will be a flop for Paccar. It is a shame because I think the engine design itself is good; just Paccar dropped the ball on the electronics. I would not buy another one.


Twitchy August 21, 2011 at 11:42 am

Well, well,

Another Benz Hater? Funny, but I drove that exact area you mention and I believe you are just another hater. What is your engineering background anyway? You seem to make a lot of statements with no real data.


Dan530 July 23, 2013 at 9:33 pm

One word “cummins” I had 5 freight shakers I only test drove them and had some guys driving them for me they all seemed to have head gasket problems and electrical problems and problem after problem after problem after problem (wack) sorry broken record any way sole all five for less then what I owed to some Indian they are his problem problem problemproblemproblem wack wack wack ok lol I have replaced them with three cummins with 2010 Pete’s only issue I have had was not related to an engine but what seemed to be driver error I run hills in Cali and Oregon and average 6.7 with all 3 Pete’s387′s and 2 389′s and 7.2 with the kw t660 with a 2013 cummins


Dale July 24, 2013 at 7:15 am

You are not the first I have heard this from. I have a friend driving the 386 with the cummins in it. He to averages 6.7 mpg. He has been very pleased with the way the engine pulls. Cummins makes a great engine.


Dale August 24, 2011 at 8:50 am

@Bob I’ve talked to a few other people who have the Paccar engine since I wrote this and they pretty much all say the same thing you have. They admit it isn’t a cat when pulling but does a decent job and they love the fuel mileage vs what they got with a cat. However like you they seem to be having a lot of problems with the emissions system on it. Several shop visits for Regen systems.
@Twitchy Yes I am a Benz hater. those engines just about broke me. Fuel mileage was nice, which was a good thing since I needed the money I saved in fuel for repairs once the warranty ran out. I replaced all the head gaskets within 6 months. Thank goodness they came out with a shim system for the liners because they were talking long block replacement at first. Engineering degree? My experience is real world with these. I don’t need a degree to know what I owned. I know what I bought, and how they preformed. In my honest opinion they were a huge mistake. And I would never buy another one. Of course I will never buy another freightliner again anyway, so it’s kind of a mute point.


pete tech March 27, 2012 at 8:09 pm

The MX engine has been a big dissapointment for our Pete dealership. We were quite open to them and hoping they would be real good. Too bad they haven’t been good so far. Power has been average for ratings. Fuel milage has been poor. We have had tons of breakdowns and fault code issues: Turbos, egr coolers, fuel issues, and sensors. The worst part as a tech is the product support is so bad. The Davie tool to read codes is a joke compared to others in the industry. Also we have to use another program to set paramiters and lots of them we have to email or call Pete to get a file sent to us. So much for a quick paramiter change. The site to look up service info is slow and lacks alot of info. The troubleshooting trees for fault codes are also poor at best and some codes have no trees. We have to deal with calling or emailing supportnet for help on most repairs and they are also poor. Sometimes they respond like they did not even listen to the question also when being told the driver is waiting or loaded the response we get back is “we don’t care about the driver”. Another big issue is SRTs (Standard Repair Times) the amount of time a tech gets paid to do a job. These times for these engines are way too low. All of these factors come down to when you do have a issue its going to take a long time to get it fixed and techs do not want to work on somthing they know there loosing time on before they start. Paccar has some major issues to fix or the fancy new factory is going to be a warehouse sooner than latter. I would advise anybody looking at a new Pete or Kw to stay away from the MX for now. The new 2010 Cummins ISX has been real good so far. Most issues we see are DEF lines and pumps which are Pete parts not Cummins. If we do have issues we can get these enigne in and out of the shop quickly. Fuel milage has been great and power good for ratings. They drive way nicer than the older ISX. Hope this helps someone…..


pete the better tech than you June 2, 2012 at 3:17 am

First off you know why they don’t let us do much at this time as far with Davie and engine pro they want to be involved with everything since new and there 1st engine. The exhaust system was designed by cummins uses same gaskets, decomposition tube, DFE doser, DOC, DPF filter, SCR, DEF pump module. Most engine problems have been EGR side with high idle times plugging EGR cooler. Electronics and sensor haven’t gave any problems core engine itself haven’t had problems either. Damn Cat engine had far more problems with regen, sensors, wiring, blown head gaskets. Cats like blowing head gaskets thanks too spacer plate design through out whole line 3406, “E”, C-15, C15, Accerts and early engines before them that used spacer plate.
None of the 07-up engines should be idled alot plugs DPFs and EGR coolers.

Chuck, MX block it’s DAF own design Paccar has owned them before MX engine come out


josh October 21, 2012 at 9:11 am

first of all the mx engine hasnt got egr the new engine that paccar are brining out in 2013 will have egr and adblue to meet euro6 standars and the only problem i have found with the engine is that after 1 million k the turbo will let go but other than that the engine is great. iv heard from drivers when they come into the workshop that they have been getting 9mpg but thats in a daf 105 xf with 44 ton on the back but in the uk the engines are restricted to 56 mph so with lower speed its easier to get fuel efficency


MX Engine Guy October 31, 2012 at 1:40 pm

The North American PACCAR MX engine uses EGR/DPF/SCR as of 2010, whereas Europe gets the EGR for Euro VI in 2014


MX Engine Guy October 31, 2012 at 1:40 pm

Meant to say that Euro VI will get all of the current North American components for 2014


MX Engine Guy October 31, 2012 at 1:38 pm

Pete-You guys have been working on these engines since the started hitting the ground in Summer 2010, so you shouldn’t necessarily need SupportNet telling you every net step on what to do. Paccar Engine Pro has made parameter changes MUCH easier and allows PACCAR to keep a parameter file on record so that if you break down at another dealer and the engine ecm (PMCI) needs to be reprogrammed, then you already have the parameters backed up on the PACCAR server. The alternative is having to manually program them in case of an engine ecm failure like you see on other brands of engines, so PACCAR is saving you all time by providing this service. By the way, the DEF lines are indeed PACCAR’s but the DEF pump is Cummins, as the MX engine and the ISX use the same DEF pump. I would suggest knowing the topic before blazing incorrect data on the Internet


GJC April 25, 2013 at 12:56 pm

Some shops are claiming that MX series is not tolerant of 5W40 Synthetics. They claim that a service bullet has been issued to that extent. Any news from the field?


Chuck May 2, 2012 at 3:27 pm

The Paccar Nx uses the basic block as the MB4000. In fact both come from a MB foundary in South America. DAF buys the block from MB. For the record, Navistar MaxxForce also uses the same block purchased by MAN from MB.


MX Engine Guy October 31, 2012 at 1:27 pm

Chuck-I am not quite sure where you got that data but it is incorrect. The PACCAR MX engine is NOT the same block as the MB, nor is is cast in the same place! The engine is cast at the Winters foundry in Germany and I can assure you that it is NOT the same as the MB, as it was solely developed by DAF in Holland over a decade ago and homologated for use in North America.


Twitchy September 15, 2012 at 8:59 pm

Well its been a while but I feel I should respond. Dale, you are correct about the REAL reason for so many supposed head gasket failures. Most were not really head or head gasket failures rather they resulted from the cylinder liner seal failing and allowing coolant to leak up onto the deck where the corrosion eventually caused the failure. I think MB knew about he issue but for those of us that had the early non-egr motors, we got the bad liner design. They eventually resolved the issues but that doesn’t change what happened to you or to me with the early design.

I had to replace all liners in my engine at 590k so I guess I was lucky. Since that time I have had no issues and I have since added a power tune box to take the HP up to 490 and I really love this engine now. You need to keep in mind that these engines were down rated to meet emission standards and if you get them turned up to where they want to run, near 500hp, they will walk all over a Series 60 on the road and in the shop. I know because I still drive mine today.

Unfortunately these engines had a VERY short life cycle here in the USA in the trucking application and aftermarket tuners and ECM programmers are in short order. If you look at the agriculture applications you will see that this engine gets very good reviews and is still being imported into the US in various ag equipment. I think that says a lot for the engine.

This engine was the test bed for Freightliner like the MX engine is now for Paccar. If Paccar takes the same amount of time, it will be almost a decade before anyone begins to respect the MX engine, but I doubt that because the DAF engine has never been on par with the Mercedes or Volvo to begin with so I think Paccar has a long hard road with the MX just like Freightliner had with the MBE.

The DD15 is a great platform today and is going strong and I have yet to see anyone write an article abut the DD series like the one you have written above. Thats because the MBE paved the way. There always has to be a starting point. The MBE was a starting point. Again, it is still a solid motor and is still being manufactured and used all over the world. I know you had some bad experiences and you are a Freightliner hater as well so let us know how that MX turns out for you!!


Dale November 2, 2012 at 12:33 pm

Twitchy I am not a freightliner hater. In fact I still think one of the best trucks made was the FLD120. Great ride, good areodynamics, etc. I did have a bad experience with the MBE engines. Not just 1 but 2 of them. Sold both the trucks and still think it was the best thing I ever did. I also traded off a new Western Star I had because of the MBE.
I personally have never driven the MX engine. I have only talked to guys that have been running them. I feel that most of the negativity regarding that engine was based on people not wanting to embrace change. And granted you are not going to climb out of a CAT engine into a MX and experience the same kind of results. The majority of the issues I have been hearing about have to do with the DPF systems. And with the newer trucks most of these problems seen to be getting ironed out pretty quickly.
I don’t hear anything about the DD15 engines due to the fact that when I got my current truck, 08 Pete with a CAT, I no longer was around the shops that worked on the DD series engines on a regular basis.
Things have quited down a lot in regards to the MX. I know guys running the Cummins engines who are very happy with them and of course I have one of the last CAT engines made for highway use. Even with the horror stories I have heard in regards to the CAT dpf system the only real issues I have had is replacing the ARD head. The system is apparently doing it’s job as I have 475K on this engine and have yet to get the DPF filter cleaned.
The Cummins engines are rummored to need the injector cleaned on a regular basis as the primary problem. The guys I know running that engine have yet to report that being an issue to me though.


Max October 10, 2012 at 4:15 pm

All in All it is a tough time to be a trucker. I run a dozen or so trucks in the southwest, all with the Mercedes engines in them (2009). What a piece of shit! I shaved my head so that I would stop pulling my hair out. My drivers are afraid to drive them as they tend to shut down in LA traffic, right in the middle of the FN road during rush-hour (always rush hour in LA) EGR’s and EGR coolers are replaced way too often, injectors start to fail a 300K miles, then the damn head gaskets and injector pumps, plastic radiators and shitty A/C components as well as the weak new front suspension and steering components are just junk. At $130K each…….and an average of 25% of the vehicles life time spent in the shop…….
So you would think that when we bought them that the salesman would have told us that or issued a disclaimer advising us that the units were pieces of shit……
We have 9 dot scales on a simple 600 mile run that my drivers have to go through making their pick-ups and deliveries with every county and city cop along the way wants to make a buck as well. And we have more and more brokers popping up from their kitchen tables across the country want as much as 25% of the rate while we bust our ass and they play X-Box wearing their fuzzy house slippers. Fuel prices are just way out of control and shippers have forgotten how to even spell “Surcharge” as tire manufactures try to hide behind the curtain pushing the price of a steer tire up over $500.00 each. Oh and let’s not forget to give an honorable mention to the “Road service” guys that need to get a big bite out of our wallet.
This is the southwest, where some idiot decided to implement the “NO IDLE LAWS”. Are you FN kidding me??? Average summer temperatures here easily hit 115 and higher, driving the “in-cab” temperature to and easy 140 degrees within the first 30 minutes. Hey I know, let’s go spend another $10,000.00 on an APU unit that fails all the damn time while trying to get higher rates to cover all of these insane costs.
Then you have the damn environmentalists blaming us for global warming…..WTF. We want better fuel economy, we want better power and reliability and we want less expensive service and repair bills…….we don’t build pieces of shit; we’re just forced to drive them.


Bert September 5, 2014 at 11:38 pm

Responding to what you were saying about APU…it’s a fancy name for a generator, and Honda now makes 1k generators that are fairly reasonable, and far, far short of your $10k price. What do you need, for HVAC for the cab, when the engine’s off? An independent A/C system, probably something the size of what’s installed in a small economy car, and a switch-over to run a small fan-driven grid electric heater system, to keep the frost off the windows in the winter. We’re not splitting the atom, here, nor mortgaging off the state of CA to some foreign country, to do this. I think both circumstances could be achieved in a total package price of $2,500, installed, a quarter of what you reported paying, and provide the operator with a reliable, quality, waranty-covered item that can provide years of trouble-free service, with minimum maintenance. Honda’s got that generator-stuff pretty much down to an art, now. A/C and heater add-on shouldn’t cost that much, and feed some generator power into a 12V inverter system with probably 1-2 standard lead-acid batteries, and you can cook your sandwich and watch TV, too. Maybe a little more design, to where you plug in the 110v at the truck center and have the same ‘utilities’, and there ya go. Designers need something to work with, a starting point, if you can define what you want/need in that cab, they can help pencil out what it’ll take to provide it. I like the idea of some inset solar panels, helping to add free energy to the system, basically.


MX Engine Guy October 16, 2012 at 10:32 am

@Chuck. I am not quite sure where you got that data but it is incorrect. The PACCAR MX engine is NOT the same block as the MB, nor is is cast in the same place! The engine is cast at the Winters foundry in Germany and I can assure you that it is NOT the same as the MB, as it was solely developed by DAF in Holland over a decade ago and homologated for use in North America.


Wayne October 19, 2012 at 9:08 am

I myself am a tech for a Pete dealership in NS Canada. I myself haven’t seen too many issues with these engines at all other then a few sensors replaced under warranty. Have talked to the drivers and owners and they find they pull decent for a 13L family engine and get great mileage. Like anything they will have to prove themselves and until they have been around for 10 yrs who will know.


MX Engine Guy October 31, 2012 at 1:26 pm

Like anything else, there was a few issues earlier on that have been addressed with a few software calibrations. The beauty of developing an engine in house is that we have total control over the development of the engine, which is something you cannot control when relying on an outside Vendor like Cummins, Cat, Detroit, etc…..


Al Veldjesgraaf November 22, 2012 at 11:17 am

an fyi For what its worth.. I bought a new t660 kenworth with a studio sleeper and all the trimmings… 4 way locks, heavy axels. 18 speed, etc I now have 75000 miles on it the big paccar engine…its not turned up full blast yet but..I am all over the us and canada east coast, west, north, south there is no area that the new whopper and I havent… it left me stranded once needing a tow… it blew a fuel line, thats it …since then there has been a recall and the problem was solved. Paccar paid the tow and the repair …not bad I think. I sold my beloved 2005 379x pete with the 475 twin turbo flashed heavy spec and turned up to 525 hp awsome truck awsome power But….5.5cdn…and i tried…the paccar ya…not the same race horse to put it mildly but the paccar does the job ok and the fuel milage is an astounding 7-8 us depends its pulling a 48 ft step tarps equip.etc… on the scale of 1 to 10 … I giver a (9)


dana fisher December 21, 2012 at 7:29 pm

i have a 2011 T660 with a Paccar 485. In one word i can sum up the performance of this motor. Fantastic. An average of 8.1mpg, 0 oil consumption. Very quiet. Great engine brake. Service from dealers has been outstanding. The only negative about this motor is the noisy air compressor. I can live with this. 490768kms and not one regen issue.


josh s January 18, 2013 at 6:00 pm

i have a 2012 kw t8 with the mx engine what a pos it has 95k on it and been to the dealer over 30 times with regen,egr,fuel lines,ac lines,oil leaks anti-freeze leaks,u name it its been there 4 it but it seems to me when it throws a code it runs like a dream great power cudnt ask for anything better then u cut it off crank it back and it derates i jus wish i cud find a delete kit i wud pay good money for one anybody know anything let me know


Andrew15 February 1, 2013 at 7:59 am

If the engine under the writer of this articles hood warranted this paragraph “The Mercedes sat lower in the chassis and you could literally tear the engine down to the block in a 8 hours easy. So ease of maintenance was indeed a fact. Now the nice thing about that is for the mechanic, and you will get to visit him a lot once the engine gets a few hundred thousand on it. Once my engine warranty expired I started blowing head gaskets on a regular basis. Nice thing they are separate heads for each cylinder.” He doesn’t have a DD15, or 13 or 16, or even an old series 60 for that matter. The reason I say this is the fact that all of the Detroit Diesel I mentioned have one head and one head gasket per engine. It’s okay if you aren’t happy with a product but you don’t have to lie about it to try to sway other people’s opinions!


Dale February 2, 2013 at 7:02 am

i had a couple of trucks that had the series 60 in them. I loved that engine. Sure it didn’t have the torque a CAT did but they did a fantastic job. My last one was in a Western Star with a 550 Detroit and a 13 speed with 3;55 rears. I loved that setup. Yes there was trucks that would out pull me on some hills. But I was steady and had good MPG out of it. The overall truck was light weight allowing me to shove 47K in the box and still be under 80K. I had no problems with any of the series 60′s I owned. Detroits move to the DD series was a mistake in my personal opinion. They had a solid engine that worked. And as the old saying goes, “If it isn’t broke don’t fix it”.
I have never driven a DD series engine. No nothing about them to say good or bad.
As far as the Paccar engines go now that they have been out a couple of years in the US market it seems as if Paccar has managed to work out many of the bugs. The few people I have talked to with this engine are reporting great fuel mileage overall. down time has been minimal on these engines as well. They have managed to get the torque up to 1850 so the pulling power is much improved over the initial 1450 introduction engines.
Of course with the new EPA standards being forced down their throats problems will arise as new technology is incorporated into the engine. I don’t feel anyone can blame Paccar or any other engine manufacturer for these problems as the EPA is requiring improvements faster than engineers can incorporate and properly test systems.
The down side to this for the consumer market is about the time they get all the bugs ironed out the government forces new rules on them that starts the process all over again.
And the MBE engine was a single head per cylinder setup. It was not a detroit. There was no lie in my statement about that engine. The MBE and Detroit are (although all made by the DaimlerChrysler corporation) different animals.


Rob March 8, 2013 at 10:15 pm

Bought 4 2012 388 Petes with the MX.

One is constantly leaking coolant. Been in for warranty work on coolant leaking 4 times. Averages 8 days in the shop for a visit. Truck has 72k miles on it. Only other problem, I think it’s driver error, keeps going through cab airbags.

Next truck throws a lot of codes & has been in for warranty work 7 times. Averages 7 days in the shop for a visit. Mostly dpf, sensor problems. 3 of the visits were for an oil cooler replacement under warranty. Yes, on it’s 4th (if you count the original) oil cooler. W/S washer has never worked on this truck for some odd reason & the dealership cannot figure it out nor will they do much about it. Truck has 101k miles on it & the driver is experienced & very tame.

Other 2 trucks have had no visits to the dealership for warranty work. They are 66k & 85k on miles.

Work: they are rigged up as winch trucks & haul mostly frac tanks around Texas, OK, NM & KS. 5% of the time they have a 53′ step hauling heavy equipment. 400-500 miles per working day except for that 2nd truck mentioned – he’s ~600 per working day. (I know, I know, I’m going to hear it from you logbook nazi’s)

Fuel: They get 6 MPG. 2nd truck mentioned gets 6.8 – driver is to thank for that, he’s most experienced & careful.

My $0.02: It’s like any new version of anything. Think of the 1st generation of iphone, dodge ram with cummins, fighter jet (okay, that’s probably a push). That first year or two, they have a lot of kinks to work out. After that, it will only get better. I think initially this will be hard to stand back & compare. Give it 3 more years (I think they’ve been around since Summer ’10), and let’s see how far they’ve gone with this MX engine. I do know the service mgr says the tech complains that he doesn’t get paid much to work on these motors & would rather look at a Cummins on his to-do list before trying mine. I’ve seen the long line of email exchanges they’ve had with techs in a tower somewhere helping them troubleshoot. I think some of that is because they have relatively new & young techs.

I’m happy with the fuel economy compared with everybody’s love for the Mack out here. Our Macks are around 4-5 mpg. I can tell you that the first ~75-100k miles vs. a Mack (oilfield loves the Mack), these trucks with the MX STILL have fewer visits to the dealership for warranty work than our Macks.

But, keep in mind – I’m only talking about my 4 trucks. Just my experience with these MX engines.


Neal August 12, 2013 at 6:48 pm

I have a 2013 Pete 386 with a 455 hp MX with an Eaton autoshift 10 speed 133,000 miles on it now. No emission problems yet, overall average mpg is 7.3 with I’d guess a 73,000 pound gross average since we top out at 79,500 as well as 62,000 gross depending on what we are taking to our plants that day. As for pulling, I had a 2005 Pete 387 with a C15 475 hp and compared to that going up hills ( monteagle tn ) it’s almost inentical 8th gear about 38 mph to the top at 79,000 gross,Town hill in PA on I 70 wb it’s about 50 mph in 9th to the top, however the engine brake on the MX holds back better than the cat did. Fuel mileage? I was getting 7.3 mpg with the cat that had 890,000 miles on it so its been the same. Now what I don’t like about the mx is that it is a bit poochy in the morning when not fully warmed up as well when it’s doing a passive regen as for the acceleration part. The other thing is with the cruise on when you roll out of a hill it will drop about 3-5 mph before it picks back up. Talked to Peterbilt about this and guess there are no settings to change. Oh and I forgot to mention this engine is QUIET! Been driving almost 20 years and this is the most quiet truck I’ve driven. Overall I’m happy with the engine, but like all emission engines I’m waiting for the problems to start. We have 10 paccar engines in the fleet and I only know of 1 that has had an egr problem at about 1800 engine hours.


Roger That September 14, 2013 at 9:09 am

I realize this is an old thread but I’m trying to gather info on the Paccar MX 13. Got a brand new 587 and my biggest disappointment
is the engine brake. Hell, I can barely hear the thing. Clearly doesn’t hold as well as the jake on the ISX. Is it a “true” jake or not? Can it be
programmed to work better? One thing I will say about the MX: the loudest thing about it is the fan…and I hear can hear the compressor “growling”. I just wish I could hear the jake…


B Sampat October 14, 2013 at 11:36 am

I am a synthetic lubricants engineer. Preferably non-hydrocarbon.

All these problems you mention and debate about would have problems minimized drastically if you were running a well made syn oil.
Not just a retail grade HYROCARBON product.

I have seen this always.


Dan Hutnick December 16, 2013 at 11:38 pm

Sick and Tired of the song and dance played in front of the smoke and mirrors puppet show Paccar puts on. We have 5 ea 389 3ea. 2012 and 2ea 2013 with MX. I would not recommend these trucks to anyone. All trucks were ordered same time with different deliver y dates. I can not believe all the lies we have been told by the Paccar rep along with Peterbilt service writer and sales. We pull tank trailers and the trucks are just under powered for this work. Fuel mileage is hurrendous, not one averages 6. Sadly we did better with 05 cat c15 turned up. These MX must have a 13spd behind them at a minimum to make up for the awesome turbo lag it sports. One would assume after spending almost one million dollars in a year that someone would listen to the issues. Negative. They don’t even return calls. When this lease deal is up or pre termination happens, switching to freightliner and I never thought those words would fall from my lips. Much cheaper unit with much better qualities.


Chris January 1, 2014 at 1:31 pm

I have 3 kw t660 with the paccar engine set at 455 hp all are 2013 models the highest miles is 190000. No real issues to speak of the one with 190000 miles is in shop now had injector to go out also had exhaust tube cracked. These trks have been loved to death never haul over 30000 lbs change oil every 10k lube chassis every 5000k miles. Kw is paying bill this time but Im concerned about these issues considering the maint history and easy life these trucks have had mileage has been poor as well 5.5 to 6 at times much worse on atleast one of the 660s Im not giving up on the mx yet but not in love either. My 3 t660s with 450 isx is much more powerful and gets 7.3 on mileage and drivers love the isx except the rattle and vibrations


Hollywood February 27, 2014 at 12:24 am

The Paccar motor sucks! I was in a 2011 KW T-660 with a 525hp Cummings owner operator specs wide open and was extremely happy! I’m now in a 2012 KW T-660 with a Paccar 455hp Owner operator specs. I average 6..2 per gallon and have no power and can’t get up hills. I have company drivers/trucks passing me. I don’t know why Paccar made such a small motor for such a nice truck. Since lack of power I try to stay on I-10 or I-20 only. I think it should be a federal law that all trucks have At least 500hp or more


kwtech March 29, 2014 at 7:49 pm

I work on the Paccar and Cummins engines and have had both on the dyno.The whole problem with the Paccar is software almost everyday they change it and due to that almost no two trucks run the same.So its either Cummins with the egr and regen issues or MX with software issues.The whole point is buy a glider and run a pre regen cat or a Detroit.


Tony October 4, 2014 at 1:53 pm

Gonna go ahead and necrobump this. I drive a 2014 Pete w/ the MX, and my only complaints are that the sensors are junk… Check engine light will come on, says the fault is “generic” (thanks genius) and then finally go out a day or two later. And the mpgs are great. But it will either pull hills like a Cummins or just flat out refuse. Some of those NC, TN hills I’ll have to downshift no shit like 4 times, with less than 35k. Even in MO, light load of 15k, downshift to a crawl sometimes. But they run great other than that. Like someone said they just need to get the kinks worked out of the electronics… Hate having that amber glow in the corner of my eye when the truck is running just fine.


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