Hey Guys,

I have a 1st Gen 91 Cummins (non-intercooled) and there is a coolant leak somewhere between the engine and the A/C unit.

I tried to locate the source, but short of pulling it off I am not able to see any one spot that is the issue.

Has anyone run into this before and know what most likely is the issue?

If so will I need to remove the A/C unit and what will I need parts wise if any?

Thanks,
Andy

 

There's a seal between the block and the bracket bolted to it which the a/c compressor bolts to. The water inlet seal I believe it's known as. It's a flat 1/8" thick o-ring, maybe 1.5" in diameter.

Yes, you will have to remove the compressor to remove the bracket. Once removing the serpentine belt, I just unbolted mine and slid it back (a/c lines still connected), letting it rest on the frame rail. You must first remove the lower radiator hose as it sits above the compressor. You'll also have to remove the heater core return line where it connects to the water inlet near the lower radiator hose. Then you can unbolt the bracket from the block and find the old seal recessed either in the block or the bracket, I forget exactly. It'll probably be old, stiff and crusty. Here's a picture of that bracket/water inlet looking at it from the block side (click to enlarge):

 

Try to use a mirror and locate the leak. It could be the thermostat housing, a heater hose, or even a coolant line to the transmission cooler if you have an automatic. Either way it helps us to help you if we know what it is you are working on. Please fill out your signature.

 

The thermastat seal on my truck has started leaking a few times, still hav'nt found a good fix for that yet, and by coincidence right under my thermastat housing is where my head gasket started leaking too, so check that spot real good.

 

You could run some silicone between the thermostat housing and the head to seal it off.

 

It is an automatic. Unfortunately, the coolant system drains pretty quickly whenever I run it and I need to get it fixed along with the wiring issues. I lose probably a half a gallon in two days.

 

I tried that, didnt work for me. Lasted a week or so. Part of the problem with mine is that I cant find a proper fitting seal for the thermastat. The original was a lot thicker than all the new ones I'v bought.

 

I think that'd be the majority of your problem. Get the right one and it should seal right up. You'll have to get a thermostat kit from Cummins to get the right seal with it.

 

Thanks guys. You have saved me a ton of time.

 

Mine has leaked at the pipe that goes over the exhaust manifold too, at the bottom where the metal pipe is clamped to a hose. I just had to tighten the clamp. Just another place to look.

 

Heres the difference between the gaskets i got vs the original. The one all the way to the right is the original. The one in the middle is from dodge, cummins also told me that is the right one. The one on the left is a felpro, same size as the one from dodge and the other cheaper ones I'v purchased in the past. The original one is almost 1/8" thicker on the thick part and is 1/16' thicker on the thin stepped down part, im not sure why the new ones arent working for me. Also the original fit more snug in the housing than the new ones do.

 

Now I know visually what I am looking for size wise!

 

What part number is it for that gasket? And Where did you source it from (The Cummins)?
The fel-pro/napa part number that I found is: FPG 35526

 

So far todate I haven't had a bit of leakage from the seals I got from NAPA. I just tried to fit a 195 thermostat into the housing a few weeks ago without success. The seal I took out was still in real good shape but I replaced it anyway. Just be real careful lining everything up during reassembly and don't put it in backwards.

 

Its RUNNING!

It turned out to be the Water Inlet Seal (i.e. the seal where the bottom radiator hose attaches to the block). Don't bother going to any of the auto parts stores to find this one. They don't know what it is and they don't have a replacement. I went directly to cummins.

While I had everything taken apart and drained, I also replaced the thermostat and seal. The cummins thermostat and gasket is also a much better replacement part. The Thermostat Gasket was not the gasket that was leaking, although it was getting very old and probably would have soon. Heck the seals and thermostat are twenty years old. Give em a break.

Then I added a coolant filter I still need to put some lume on some areas to protect some hoses etc. But it is mostly done now.

I attached some pics.

Thanks for the help everyone especially to jimbo--you nailed it on the head.