Khaosinc

Hi there, Im a mopar junkie who has mostly stuck to pre 70's rigs. I recently retired the '57 powerwagon (for restoration someday) and found (what I hope was) a good deal on a 90 3/4 ton cummins to have something reliable to haul cars with. The issue being a water leak in the front of the motor somewhere.

The bracket to the right (drivers side) is covered in dried coolent. Can't really tell where its coming from. Pumping up the cooling system with my tester reveals no bleed down, no water in the oil, but she will loose a noticable amount of coolent on my drive to work (40 miles)

Question:.

The leak is clearly not in the water pump area, and is under any of the hoses in the area. DO any of the front bolts go in to a water jacket, or is there any other sourse of coolent in that area other than the head itself. This is a 150K motor, that has had its share of hauling but has never been modded.

Second, My sevice manual is en route, but is changing the head gasket in a deisel any different than a gas engine? as that seems the only other place for a leak.

I'll be poking around here for a while, as this old girl needs some power next...this truck seems gutless compared to the old 331 hemi in the 57... can't have that.

G1625S

Welcome to DTR! Good to have you aboard. From what I've read, you've most likely got a blown head gasket. Someone else will chime in on the possibility of a head bolt going through a water jacket...not sure on that one. As for the gasket swap, have the head machined like any other, but know that there is an 'acceptable' amount of cracking according to Cummins. Deal with a machine shop that knows diesels and you should be ok. The head is quite heavy---have a few friends there to help pull it off, or an engine crane would even be better. Once you get the head sealed up and tap in to some of the available free power under the hood, you'll find yourself wondering why you even own any gassers, hehe. I've got a mini collection of old iron--see my signature. Good luck with the truck--keep us posted!

Greg

andyr354

any pics or a better description of exactly where the leak is?

Is the thermostat housing leaking possibly?

My head seeps slowly at times behind the thermo housing, from what I have read this is quite common and I don't worry about it.

If an external head leak isn't terrible and you aren't getting compression from the engine in the radiator, you can run with the rad cap loose and it will usually quit leaking.

goodtyms

Welcome to the board! I have found a wealth of information here.

I, too, had/still have the same problem as you. Mine turned out to be a common water jacket-only head gasket leak. From my research here and other forums, I’ve found that it’s quite common for the Cummins head gasket to leak between #5 and #6 cylinders. I originally thought that it was my T-stat housing and changed the gasket to no avail. I finally pressurized my system and looked very closely at the head gasket (after thoroughly cleaning the engine) and found that the head gasket to be leaking. It seemed to vary a little, depending on if the engine was warm or not, but it was the head gasket.

Many people will tell you that the head bolts are torque-to-yield and therefore are single use. Also, especially if you intend to Bomb (the term used for performance mods), but even if you intend to leave it stock, you might want to consider replacing the head bolts with studs. That’s what I chose to do - I’m just waiting on the brown truck to deliver them. They aren’t cheap, but neither is doing the job twice!

Let us know what you find.

Khaosinc

I've always replaced head bolts when doing gaskets, as (like you said) I don't like doing anything twice. I've liked driving the truck so far, but stock I've found it a little gutless compared to big blocks and early hemis. I'll be looking for this 'mysterious' bolt I can turn up the turbo on soon enough.. but thats for another thread. Actually stumbled on a deal of another cummins w/ 727... so I'm half toying with putting one in the old 57 as well.