5.9L vs 6.7L Cummins: Which One is Actually Better? 

Its all about the mechanical 12 Valve 5.9 man. A true LEGEND.

I have 2 of the 5.9 / 12 Valve in 1 ton trucks I uses on my farm and I love them. I retired from Union Pacific Railroad as a electrician. The newer Technology is great as long as you have a standby mechanic to keep it running. Union Pacific Railroad uses older Locomotives with mechanical blowers in there Local switch yards till about 2012, because all you had to do was fuel them check the oil and run the shit out of them. They were bullet proof.

Owned both and have love for each of them. 6.7 will work if deleted and I would recommend arp head studs. The 68rfe 6 speed automatic transmission is great when working but prone to failure with hp increase unless built. The g56 6 speed manual transmission is probably more reliable but not as much fun on the street. Like said in this video the 5.9 is more reliable but has some disadvantages too. If I was going to have to pick between the 2 I would pick the 5.9 just because of its overall reliability. That being said I really do love them both. Just my opinion. To each, their own.

Went from a 6.7 to a 5.9. I tow aprox 70,000 a year. Don't want to up set 5.9 folks, but for my need I've found 6.7 to work for me better. My 2010 6.7 provided me with 210,000 miles in that stretch I replaced 2 water pumps 1 alternator. All other repairs were not done on the power train. The truck I'm currently piloting is a 5.9. It works ok, but I have had to adjust my trip times as I'm slowed more often than in the past. I also have a hard time maintaining an exhaust gas temp that will not damage the truck. Learning to drive with new limits is I guess a personal problem to get past. The up side to this new, to me 5.9 is the fuel mileage. My new 5.9 gets almost 50% better mileage. That is the main reason I'm keeping it.

My wife and I are full time musicians and full time in our 26 foot travel trailer (30' overall). We pull it with our 2007 3500 4X4 with a fully enclosed fiberglass CargoBody cabover work van style camper. We sought out the last 5.9 (early 2007) for it's better mileage. With the cabover semi-empty (around 700 lbs) at 55 mph on level freeway, we got 25.5 mpg. Now that the camper is full of tools, and pulling the trailer (8,000 lbs), were averaging just shy of 16 mpg, which is where the 5.9 really shines, especially now that diesel is so expensive!

Being a former diesel mechanic I love my 5.9 24v because it is so simple. With the NV4500 trans it makes all the power I will ever need and no repairs after 20 years .The only weak link is the lift pump starving the VP44 injection pump. A good fuel pressure gauge and keeping the filter changed is so important. Unless I wreck it it will be the last truck I ever own.

Simply put...the 6.7 was needed to achieve more power but still meet the more and more stringent emission requirements than the 5.9 could. The 5.9 is still the dominate engine in the performance world.

Hey man, i have been watching a couple of your videos recently and just wanted to say your doing a great job. Thank you for your clarifications and knowledge on the subject, you explain things very well and i just wanted to say job well done.

Why so much footage of mall crawlers?

Wow, you answered my question and more. I've always liked the 5.9 though.

5.9 cummins better

Thanks for the input. Just looking to tow. Think the 5.9 with no emissions is probably the way to go.

5.9 24v with p7100 most power and reliability for ever

Never owned one up until now my 6.7 89k miles seems to run great and I can feel the power it has.

I have a 2001 5.9. Straight up the 5.9 sounds so much better. I still love it when I go into parking lots and heads turn. Obviously sound doesn’t mean it’s better but I like it.

You can upgrade the 6.7 by installing the 5.9 head, injection system, and ecu. Firepunk Diesel has a video on that While there may be some benefits to running the stock vgt turbo you will quickly find its disadvantages if you’re going for maximum power. It is actually quite inefficient with a high drive to boost pressure ratio so even if you’re running your truck basically stock you’re still better off with a relatively small fixed geometry turbo (BorgWarner S380 or S400) There are a lot of other parts that interchange on these engines such as water pump, oil pump, camshaft, valve train, front cover, etc. The 6.7 will bolt in to a previous generation truck with no modifications. This video mentions head gasket failure- the 5.9 head gaskets have been known to hold very high boost pressures even when using oe headbolts this is not the case with the 6.7 Both motors can make over 1,000 hp with compound turbos and larger injectors. Pretty much the only reason for Dodge to make the switch is emissions control. This increased displacement allowed them to comply will still competing with Ford on power output

I have more than 1 Cummins engines with emissions still intact and operational with over 750,000 miles and a couple over 1,000,000 miles. Requires more maintenance but doesn’t make them unreliable.

I really love the detail you guys put in the videos. 1000 tq from factory is crazy! I like the 6.7 more. How about a video about the VG30DETT?

Got an 06 5.9 24 valve mega and love it. But those older 12 valves just sound better!!

Great video! I have a 1999 2500 5.9 since new. Currently at 392000 miles. I've pulled everything under the sun and I am still on the original automatic transmission. Only problem I've had is the VP44 injector pump. The last VP44 I replaced went 170000 miles on it. I changed the lift pump out every 60000 miles regardless to keep the VP44 alive. I am in the middle of refurbishing this old gem and started out with a Fass lift pump and new injector pump. It's been an amazing truck!

I have the 6.7 on our ranch. Pulls heavy trailers with livestock and/or feed and it works great. The trucks in this video... A laughing stock to an American producer. Stay in the city and keep pretending food comes from the back of the store.

Case IH has a 5.9 cummins. I really like how efficient that engine is. Still use that tractor and it's 33 years old.

I'll take the 5.9 common rail. 325hp, 610 torque out of the box. And who needs all the black smoke 🤢? That's just fuel out the tailpipe.

One thing about the 6.7 is the rod angles which is a weak point vs the 5.9. 6.7s bend rods easily when lots of fuel is dumped at low RPM. Would be a good idea to go with forged rods if you're pushing more than 1800 ft lbs of torque on a stock 6.7 bottom end.

That's like comparing the 7.3 and 6.7 Powerstroke It all depends on what you want in power In both cases the 6.7 is superior

5.9 cummins is by far the better engine my uncle has a 2 6.7 cummins and emissions are killing his trucks and he had a 5.9 and had no problems

We wanted something simple with no def so we bought a couple of 5.9’s ( 2-24 valves and 1- 12 value) and they have been great.

As a Cummins tech I will tell you a 5.9 has it all over the 6.7. Just a 12 valve 5.9 will net you 50% more than a 6.7 and it’s all mechanical. Zero issues.

I've had and worked the heck out of both and the 5.9 is more reliable and better mpg and I think it sounds better but the 6.7 is still reliable but when you get rid of all the bull shit on it it's definitely much stronger

I own both a 2007, 5.9 and a 2018 6.7. Love them both. My 2018 is a manual and 2007 automatic. The 5.9 seems to pull better in ice and snow without the tires losing grip. The 2018 tends to over power and spin. The 5.9 had about the same fuel economy as my 6.7 driving from Alaska to Texas. With both pulling roughly 1300lbs of weight. I did delete my EGR and DEF and added some tunes to my 6.7. Which greatly increased my fuel economy and saved money not buying DEF fluid all the time. Now I hunt in my 5.9 and pull my ATV’s. My 6.7 I pull my 5th wheel on long highway trips.

i like my 12 valve hands down did a swap.out last year from a 6.0 powestroke to the 12 valve with the p pump i love it so reliable and it sounds sooo good too

I'll take a deleted 6.7 anyday

This is a joke of a comparison. Comparing pre emissions to post emissions is apples and oranges.... and lets face it the old 5.9 12 valve that is quickly eliminated from comparison here is the only one of the engines that can get 25-30 mpg and run a million miles... mainly due to... yup NO EMISSIONS, and mechanical everything.

I'm very happy with my 08 6.7. Full delete, banks turbo and efi live tune. I went with a modest 100 hp increase. All the power I could dream of and 21 mpg on on long trips with cruise set at 70 with a 6 in lift and 37's. I've had no issues with it in the 3 years ive had it. I run Delvac and change the oil and filters every time I service my freightliner. Intervals are usually 4 to 5k.

Hello, as someone else said that the all mechanical 5.9 is the best. 91 N/IC stock with a bit of added timing I regularly obtain 20-24 MPG, replaced the 727 (37RH) to a 46RH with 3.08 rear gear set 335800 Miles on the ticker. I don't ever expect to sell and oil samples show minimal wear, 1.5 Million miles expected (ill probably die before that). Best purchased I ever made and great mileage. Love that pickup and still in todays road climate I love to drive it. Pretty darn good for an old beast.

This emissions crap needs to end

Also need to take into account the transmission options available for both. 5.9 48re and g56 or 6.7 68rfe aisin and g56 the 48 is an awesome trans

Thanks, great comparison. Myself I prefer the 5.9 for reliability, and better fuel economy in general. My 2002 LB/4X4/4 door was getting about 24 MPG with full cab and bed (not towing).

I love my 2004 HO 5.9 dually. I am the original owner and am considering the new 2019 HO 6.7 but my 5.9 is part of the family and has earned her keep.

The 2003-2007 actually does have egr. It has in cylinder EGR via the camshaft. The lobe separation anges are closer than on the pre 2003. 98degrees vs 106degrees I believe. Closes exhaust valve a little early to trap exhaust gas.

Also you have to take into consideration of the ho second gen they’re kinda rare but mine has 535000 miles on it and only been through 2 fuel. Pumps 1 starter and 1 turbo but if you’ve ever been in the ho second it’s a totally different animal

My dad had a brand new 05 5.9 for pulling a toy hauler to the dirt bike races when i was in high school. When i got my liscence in 2008 it became the truck i got to drive around. To this day it is my favorite vehicle, I’m looking at buying another one now. I currently have a GMC sierra that needs something new fixed one thing after another.

Some guys swapped parts from the 5.9 to their 6.7s and ran them with the vp44 due to emissions. Said driveability was improved The 6bt debuted in Case heavy equipment. One can source parts for the one on the dodge from them.

I have a 1991 Dodge duly 35 runs great never had any issues I have over 1,000,000 miles does not smoke clean body and motor I just recently changed the fuel pump injector pump rebuilt it put a new one other than that no problems runs great

2:51 that 03 dually in the back tho

I would love to see this on another platform.

Well done video

This video gives me heartburn 😂

My 1st 06 was so reliable and powerful I had to get another one, I have had 211 vehicles and the 06 dodge 2500 has by far been the best and most reliable

It's a great thing about a non-inspection state you can do whatever you want to your vehicles

I had a 1996 12 valve and have a 2004 common rail. Both awesome engines. For reliably I choose a 5.9. But I would be just as happy with a 6.7.

'97 5.9 12 valve with a "P"pump for the street & 4WD

2006 5.9 is a great platform for those who want great reliability and the ability to make great power without hurting the pockets; G56 manual trans is even more desirable.

I have a 5.9 12 valve 398000 miles pulling fairly strong yet and a 6.7 203000 pulling strong yet both start without hesitation in the cold Wisconsin winters. I love them both for there abilities and reliability. The best of both worlds.

My dad has a 2004.5 5.9. He pulls his 31ft camper with it. And it’s a beast. Almost 200k miles on it and still runnin strong.

6.7 with vgt is in another league towing heavy, and the 6spd at with it makes it so much better than any 5.9 truck ever dreamed of being The 6.7 doesn't "blow head gaskets", the owners do when they push drive pressure beyond the compressor map safe efficiency range, by running super duper cool race car tuner boxes to add 300 hp Anyone who says otherwise has never used both, the 4x4 5.9 trucks in tow mode are screaming at 65mph, while the 6.7 truck can tow in 5th or 6th and run 80 loaded to the hilt at an easy rpm, although 5th is better for it obviously The riced out trucks at the beginning were definitely comical The 5.9 has no emissions garbage so it will always be called the more reliable engine, but the dpf has nothing to do with the engine being reliable or not, that's a totally separate emissions system.. They're both the best engines to have ever been put in a light duty truck and probably always will be...

I have a 1995 5.9, best cummins by far.

I have 3 notes. 1: the term is destroking where they’re putting 5.9 cranks into 6.7 blocks. Resulting displacement is 394ci. 2: The vgt uses the same 60/86 compressor as the 04.5-07 5.9’s, and the same turbine wheel (I’ve measured many of them, they all fit in the same hole, but there’s a 3-4mm spread in inducer/exducer measurements), and the vgt itself is primarily there to facilitate ego by creating higher backpressure. 3: head gasket failures are principally due to incorrect injection timing. Basically to much timing for the fuelling puts the pressure spike too close in the wrong spot. My preference is the 6.7 due to its ability to spool significantly larger turbos with ease.

I would be interested in knowing the difference between the 6.7 engines before and after the DEF fuel system was added. I have a 2012 model, which was the last year of the pre DEF models

Had to stop the video could not look at those "trucks" anymore

5.9 sounds alot better then the 6.7 Cummins

The he351cw actually is variable geometry. The solenoid on the side activates and moves a gear which moves the vanes.

I have my 5.9 24v, for 14 years, only had to change the water pump, belt tensioner , fly wheel sensor, clutch and belt few times. Now is in his 494,000 km, at is still purring like kitten. With Lucas oil, engine running more quite!

12 valve Cummins is still the king!

How I see it both are good but Fall into different categories the 5.9 for towing /traveling the 6.7 drag strip racing and messing around but at the same time both can do the two things 🤷‍♂️ just my opinion

A very good video. Very good ad giving a definitive answer though 😉 tuners favour the 5.9 due to epa restrictions. As a UK ram owner, I got told by a US tuner, keep the 5.9. They don't make them like that anymore.

I just bought both lol got a 89 5.9 and love it all around I bought a 2012 brand new and love the power the 89 is stock the 6.7 is deleted and tuned and I have put over 200k on the 6.7 and pulled a lot of heavy heavy things and I don’t treat her nice and not a single break you must build the truck for the task your using it for to get the best truck

Honestly. I think all turbo Diesel engines are pretty amazing. They each have their flaws, but all can be made “bulletproof” without a whole lot of money. I have a 2011 F250 with the 6.7 diesel. I’ve done a few things to prevent failure and it’s been nothing but outstanding work truck and fast. I love the Cummins and duramax seem great too, Allison transmissions are always nice. But a lot comes down to maintenance. Diesel is a different beast. Myself, I like to drain my fuel filter every so often and replace them bout every 3 oil changes. Most people won’t and bad things happen

Love my 05 3500, 5.9👍♥️🇺🇸

'02 24v with HO 5.9 engine and dreaded VP-44 pump. I did have the OEM pump give me problems at ~ 65K miles but it never quit. The dealer swapped it out under warranty and it cost me zilch! At 165K we're still running strong and I wouldn't trade this rig for anything new on the market. With Bosch RV injectors and a Quadzilla mileage chip I'm pulling around 320 HP and >600 FT lbs of torque. I can keep up with most anything on the road and get a steady 19 MPG (that's with 1000lbs of camper in the bed). I'll keep this one thanks!

Have a 1993 D250 cummins, 180,000 miles in and still has cross hatching somehow. 20 mpg, 300 horsepower, it’s a dream to drive.

12 valve for the win

This video should be titled “The difference between 5.9 and 6.7 Cummins”.

Bought a Ram 99 CTD new, in dec 99. Put 241,000 miles on it in 5.5 years. Engine was solid, lift pumps...not so much lol I think I went thru 4 of them. Also spring a shaft leak on the VP-44 ...I attributed that to my switching between hi and lo sulfur diesel fuel a lot (yes, I ran off road 3,000 ppm sulfur in it as well as on road 500 ppm - and sometimes BP Diesel Supreme which touted 50 ppm sulfur) So I think this up and down sulfur content caused the shaft gasket to deform giving me a fuel leak into the crankcase. Luckily I bought it early and did no internal damage. The CTD 5.9 24-valve Was a great engine.

Have had 3 3rd gen rams with 5.9s and 48REs. Great trucks. 1st one was all stock and beautiful. No complaints. 2nd one was 300k miles and I built it to the T and it made 749whp with room to go (didn’t want to blow up my 300k mile block) also took lots of trans work and the front end was poop. 3rd one just had a smarty touch, Intake, exhaust and mild trans build, good truck. I now have a 2021 6.7 and it absolutely destroys the 5.9s in power department. 6.7 deleted is 100% superior in my mind

5.9 is EMP-proof plus more MPG.

I've owned all three models of the engine and understand each was a well thought out natural evolution of the prior ones. My 12 valve had 400K on it when I sold it and its running around yet today. My 24 valve 5.9 was just as dependable but suffered from poor quality components such as step pump and water dispersal system. My 6.7 has ran flawlessly for 188K with only minor issues with the TIPM. Cummins is in a different league than the competition so any comparison is pointless.

the company I work for has 2 capacity shunt trucks one with a 5.9 and a 6.7 and both seem to preform the same when moving loaded trailers around so I think their both great

Thanks for the vid. I always wanted to know the differences. Sounds like both engines are good, it just depends on personal preference/use. For me, I'm glad I have the 5.9 version for reliability as I have no need or desire to add any performance mods. I have an '03 3500 Ram dually 4WD with the 6 speed manual I bought used in 2009 with about 55K miles on it. Almost 12 years later now, it now has a little over 135K miles on it. I only use it for travel. One year it sat for the whole year in the garage, which wound up costing me over $400 dollars to replace the Optima batteries. I now take it out once a month for a short drive, about 30 -50 miles to keep everything working.

Hands down the 5.9 I have an 07 with 445000 miles and all it’s had is a 2 clutches and 1 transmission and I use it daily for cross country towing

I love my 93 dodge d350 5.9L v12 Cummins

I wouldn't trade my 2005 Ram 3500 5.9L Cummins for love nor money. Still going strong. Service and replacement parts as needed. Almost 300k on the clock and still tows and pulls like the day I bought it.

I've own Mopar since I started driving in mid 70's. Challengers, RR's, Fury's Chargers, trucks etc. I've been away from classic auto seen for awhile now / was looking for a project. I found an unmolested bone stock (except 35's and aftermarket radio), 97, 5.9 P-pump w/5sp with easy 222,000 miles no rust CA truck. From reading the comments... I think that I made a good choice. Thanks for the upload.

5.9 is a more reliable engine, more fuel efficient, however the 6.7 pulls and works so much better! I’ve owned and worked both.. as a daily, I’ll take my 06 5.9, if I’ve gotta haul heavy weights and push a lotta wind I’ll take the 6.7 hands down.

I own 95 12 valve 5.9 stick Also own 08 6.7 450 auto deleted My fav is the 5.9 virtually bulletproof ... although having great issues maintaining the body

Got a 08 6.7. Love it to death stacked chips, fully deleted. Sound is amazing with my 5" turbo back and 10" dump tip.

I have had both and I do have to say the 6.7 definitely has a lot more power but mine did blow the head gasket and injectors. To where my 5.9 hasn’t had those problems. But my 5.9 did need a transmission rebuilt and the 6.7 didn’t. So it’s really a toss up. I do know that you can tweak the 5.9 motor to add more power really easily. But it just depends on how much you want to spend. I believe both are great motors

you have the injector firing voltage backwards. We are working through this issue trying to run the more reliable 6.7 injector in a 5.9 truck running the 5.9 ecm. The 5.9 injectors fire at 18v and hold at 18v the 6.7 injectors fire at 24v and hold at 18v so we are getting a sluggish opening on the 6.7 injectors causing a rough start.

Just went over 310000 miles on my 97 12 valve still running like new

I my friends have 3 Rams with the Cummins to this day. Never sold one yet. 2004.5 48re - 2005 NV5600 - 2014 Aisin

Vgt is used to create higher exhaust pressure to get exhaust gas past the egr value into a boosting situation. The benefit is less turbo lag

5.9 cummins not as computerized

12v 5.9 pretty bulletproof

I have a '93 D250 with a bone stock 5.9 12v and the 5-speed Getrag tranny. I've owned it for 12 years and it just turned 200k miles. I've never done anything to the engine but change the oil, oil filter and fuel filter, flush the coolant and adjust the valves. I'm now thinking of bumping up the power a little, but I don't want to get to the point where I need to change the clutch out or overpower the rest of the drivetrain. I just want to be able to keep a little more speed while climbing grades with my truck camper and towing my car. I'm searching for a video that explains in detail the process of turning up the fuel screw, adding a custom fuel pin and different governor spring. I've worked on my own vehicles for 50 years, but have never done anything like this to a diesel. And I've read of some others trying this but ending up with an engine that runs worse than before. Trying to decide if I need to take it to a diesel mechanic instead. Can anyone recommend a good video explaining the process?

i owned a 98 6 speed single cab. traded it for my 03 auto. later bought a 13 auto. other than the transmission in the 03 its been a hell of a truck. still have it and the 13. wish i had never got rid of the 98 tho. as far as pulling that thing was a beast. if i could find another one in good shape i would buy it in a minute. far as the engines go i would trust the 5.9 over the 6.7. plus you dont have to spend $7-$8000 deleting them to start adding power.

I vote for my 98 12 valve with a swapped in 6 speed manual,reliable, makes decent power ( not much done besides fuel plate) and gets great fuel economy Oh an I almost forgot P pump baby!!!

I guess my rusty bone stock 03 with 201k miles wouldn't be allowed to be on this video.

FANTASTIC REVIEW LOVE IT-LOVE BOTH -THE 5.9 & 6.7 ( WOULD LIKE TO GET AVERSION EACH OF THE 5.9 ) 12 VALVE & 24 VALVE.

I have 04 common rail cummins 150,305 miles on I know its not broken in yet but I love that truck just put new injectors in it a few months back back but I don't think I could replace that truck anytime soon

I love my 5.9, it’s a beautiful motor. Does everything I ask of it. Maybe when I trade her in I’ll think about the 6.7 but honestly I plan on finding my same truck just with less miles.