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

The 5.9L is a little bit more reliable and lacks the annoying emissions components which plague all modern diesel engines, but the lower displacement and fixed geometry turbo limit performance unless you add a different turbo.

The 6.7 has more displacement and a larger variable turbo, allowing it to make more low-end torque and more top-end power, however, it’s more to head gasket failure and the emissions components occasionally cause issues.

If you think reliability is the most important feature of an engine, the 5.9L is the better engine, however, if you’re interested in outright performance, the 6.7 is the better engine. Of course, this video mostly omits the older 12v engines with fully mechanical injection systems which are known for being crazy reliable.

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[JillandKevin]

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!

[dieselbroke]

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.

[bootmender]

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.

[mongo]

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

[billhouse]

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.

[jssomewhere]

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.

[everettivey]

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.

[Crazystuffyousee]

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.

[jondavidbristow]

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

[zakman]

I first tried to become knowledgeable of the 5.9 and the 6.7 Cummins Diesel Engines . This was in the 2000 teens . After my research I felt the 5.9 Cummins Diesel was and is a more reliable diesel engine . So I shopped around and looked around at nice good Dodge Ram Trucks with the latest 5.9 Cummins Diesel Engine . A lot of looking around because so many people abused every kind of truck that was for sale and didn't matter the manufacturer !!! Which added to my searching !!! After 3 years of looking, I found what I was looking for, a nice clean good Dodge Ram Diesel Truck with the very last of the 5.9 Cummins Diesel Engines ! It's a 2007 Dodge Ram Mega Cab with the 5.9 Cummins Diesel Engine, rear wheel drive which has the better fuel mileage !! I bought it and have been extremely happy with my truck !!! Problem free, as long as you keep up on your normal maintenance of course . It pulls great from 30+ foot 5th wheel campers to 30+ foot gooseneck trailers and smaller trailers including car hauler enclosed trailers . It's been the most reliable truck I have ever owned with all the miles I've driven it !!! I talk to many owners and drivers of the 6.7 Cummins Diesel and they tell me of all their problems and break downs . Where I don't have any problems or break downs . So I am extremely happy to luck out finding my 2007 Dodge Ram Mega Cab with the last of the 5.9 Cummins Diesel Engines !!! It's a work horse of a very reliable diesel truck !!!

[samhughes]

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.

[jmandella]

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.

[amosesh]

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

[jpag]

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.

[TheCustomEverythingChannel]

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

[zachmccall]

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

[trentjones]

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!

[scooter]

5.9 24v with p7100 most power and reliability for ever

[rogerray]

Have a 1991 D350 with the 5.9 12 valve. Purchased new on Halloween Day in 1990. Now has 486, 000 miles and still going strong. Replaced the water pump, alternator, starter at 400, 012 miles. Nothing else has been touched on the engine. Still gets around 22 miles a gallon unloaded and about 16 mpg pulling gooseneck with 580 Case backhoe. Not a speed demon but gets the job done. Also have a 2007 3500 with the 6.7. I've constantly had wiring harness problems, and injector problems, head gasket replacement and other items throughout the truck with only 125, 000 miles. It's a great truck when it runs but not trustworthy so I'll stick with the 5.9 12 valve.

[gunfreak]

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.