Cat C7 vs Cummins 5.9

[abrasv]

Going today to look at an "02 Discovery with the Cat C7 engine and also an '00 Discovery with the Cummins 5.9 engine. Both have around 50,000 miles.

I have heard the horror stories about the C7 and problems with the Huie (sp) systems and the cost to fix them when they go out. I have also heard the C7 is a non-rebuildable engine whereas the Cummins 5.9 is more reliable and rebuildable.

I have always had gas units and am wanting to go the diesel route and am seeking advice on both these units.

Those of you that have them have the experience and I would like to draw on that before making a decision to buy.

Thanks in advance,
Jim

[RustyJC]

The 5.9L 24V Cummins of this vintage uses a Bosch VP-44 fuel injection pump. This pump utilizes excess flow of the fuel itself to provide lubrication and cooling, the latter being especially important since the VP-44 carries its electronics in the pump assembly. Therefore, it's essential to never let fuel inlet pressure to the pump drop below 8 PSIG, which can happen if the fuel lift (transfer) pump goes bad. On the Cummins 5.9L engines of this vintage supplied to Dodge for the Ram trucks, the lift pump was installed on the engine itself and subject to the heat and vibration inherent to this location as well as having to pull the fuel forward from the fuel tank (this pump is more efficient as a "pusher" than a "puller"), so these lift pumps were prone to failure and should be monitored. This is done with a fuel pressure gauge installed so that it sees the pressure at the inlet to the VP-44 injection pump. If the lift pump stays healthy and doing its job, the VP-44 will generally stay healthy as well, but if the lift pump goes bad and fuel flow to the VP-44 drops, it can take out an expensive VP-44 in pretty short order.

As far as being rebuildable, the 5.9L B-series Cummins (unlike the larger Cummins) is a parent bore engine. This means that it does not use replaceable "wet" cylinder liners, but rather that the pistons run in cylinders bored into the block itself. If a piston fails and damages the bore or if abnormal wear occurs, the block itself has to be bored and oversized piston(s) installed, or the block has to have a dry liner installed to use a standard piston if only one hole is damaged. The upside of this is that the 5.9L Cummins is NOT subject to cavitation and doesn't need coolants with a cavitation inhibitor.

At 50,000 miles, if properly maintained, the 5.9L Cummins is just getting broken in. These engines can go 500,000 miles or more between rebuilds - there are any number of Dodge trucks in "hotshot" or other high mileage trailer towing applications that have over a million miles on these engines without rebuild.

It's a good diesel IF you know what to monitor and do it.


Rusty

[Chaffeekid]

I have the Cummins 5.9L in my Expedition and love it. It is the small one, 260 HP and gets really good fuel mileage even when pulling my Dodge Ram Crew Cab 4 X 4. It starts and runs with no problems and pulls the 36T with no problems.

It has the rear radiator, and havn't had any problems with overheating, or throwing oil on the Toad. We recently returned from about a 1000 mile trip and averaged around 10 MPG which I thought was really great.

The Cummins 5.9L that I have ISB is not a wet cylinder engine so you don't have to worry about cavatition or pitting of the cylinders as you would in a wet sleve engine.

I owned and drove a couple of 18wheelers with Cummins engines so I am partial to them, had almost a million miles on a 1995 Freightliner, and 750,000 on a 2000 that I bought new, never had a problem with the engine and both were still pulling strong when I sold them. Course I did all the maintenance on a regular basis.

I just like that big red engine, yellow is not really my color
Happy Trails
Jim, another Missourian

[Chaffeekid]

Good info Rusty, does the ECM monitor the fuel inlet pressure to the VP44 and do you think the new Scan Gauge D would show fuel pressure provided by the lift pump.

And you are 100% right, my lift pump is located on the engine.

Had to change the drive belt on the AC compressor, man that is a job. And the 40.5 belt specified by Freightliner won't fit over the fan. Takes a 43.5 to do it. FYI

Happy Trails
Jim

[abrasv]

Really good info on the Cummins. Looks like (as I've heard) a very reliable engine if it's maintained.
I've looked at the '02 with the Cat last week and really like it but at this point the engine is my biggest concern.
Looking again today and tomorrow at both.
Jim

[RustyJC]

Dunno about the Cummins ECM on the MHs. This Cummins-supplied ECM is completely different than the one used on the Dodge Ram trucks - fuel inlet pressure to the VP-44 was NOT available on the Dodge Ram CANbus.

Rusty

[Mooseguy]

Don't know about the Cummins. Don't know much about the C7. But I have a C7 in my Fleetwood and have not had any problems. Not sure about the rebuild but I will probably not have it long enough for that. It has plenty of power. Sorry not much help.

[michelb]

Personally I'd really like to have a motor home with the ISB5.9 simply because of the mileage but there's a lot of people that feel that it doesn't have enough power (depending on which one you get, it's about 200-300 ft-lbs of torque less than the C7)

[henderson]

I believe the '02 Discovery has the 3126 cat engine the C7 came out in '04

[hooverbill]

Originally Posted by michelb

Personally I'd really like to have a motor home with the ISB5.9 simply because of the mileage but there's a lot of people that feel that it doesn't have enough power (depending on which one you get, it's about 200-300 ft-lbs of torque less than the C7)

Yep, the 5.9 is a good little engine...that's the only problem...little.

[rvarner]

Not much power with a pickup truck engine in a motorhome. My friend didn't much care for the power in his 2000 Allegro Bay with an ISB and wanted to install a chip in the engine. Great engine tho and very reliable. Look for a coach with an ISC or better. You can't have too much power.
Richard

[JPMaly]

I owned a 99 HR Endeavor with the cummins 5.9 and now I own a 03 Jayco Avatar with the Cat 3126. The cummins got great fuel mileage, even when towing Honda Element. However, it lost all game trying to pull any slight grade. It also had the dreaded 53 block ( do a search ), so I did not feel comfortable adding a banks kit, though some do. The Jayco has 330 hp ( 55 more than the 275 cummins) and 840 lbs torque ( A plus 180 over the 5.9) I can pull the Cajon Pass, 55 mph at the weigh station and maintain 55 to the top of the hill. Avg 9 miles per gallon. I think the 02 is a 3126, slobber tube and most likely has a grease zirk on the fan pully, mine does. One could never have too much hp, but remember, more horses, more $hay$

[Jim_HiTek]

Yes, the 5.9L B Cummins can be a nice little pusher, but the earlier models have the 'Killer Dowel Pin' issue ('94-'98?), and the 'Oil Cooler Leak' (years unknown) issue among others with no word that I've ever found that they took care of those issues in later models. Makes it hard to jump on the Cummins bandwagon with a refusal (as mentioned by posters with these problems) by Cummins that there might be a little problem here and there that they've since addressed.

What's waiting around the corner on newer models? Are their RV models a little less 'reliable' then their truck models?

[stuhly]

Either one of those engines are capable of 500,000 miles if you take care of oil and air filters, and drive it in a reasonable manner.