M43 (M37) water pump leak. Odd....

[Irv]

There is a water leak up by the water pump. I thought it was just a bad pump and replaced it. Still leaking. In fact, last year a leak formed and I assumed it was the pump going bad, even though I had replaced it recently. Figured that they do go bad from time to time. Bought a rebuilt one from NAPA (get the so-called "good stuff") and a friend installed it. It leaked. I removed it, cleaned it like you could eat off of the gasket surfaces, reinstalled with lots of Permatex, just in case. It still leaks. Not sure why, but it appears that the leak is not from the pump at all, but maybe from the head? Can't really tell where it's leaking, because there is so much water. Almost looks like it's coming out of the weep hole.

Is there some typical leak on these beasts that would explain this? I'm starting to think that the previous pump also did not leak, but we were fooled by another leak from somewhere. Ideas? Head gasket, maybe? Thanks.

 

[M543A2]

You got me here, but a suggestion. Can you make a metal cover to cover the pump opening with the pump removed and refill the block to see if you see the leak origin? It has been a long time since I had the pump off one of these, so I don't know if it is possible, but it might help give a clue if it is.
Regards Marti

 

[citizensoldier]

You could have a blown head gasket? Can you take some pictures? Has it been real cold before this started? Is your antifreeze up to spec? What weep hole?

 

[M813A1]

Sometimes in cold weather the hoses will leak a little bit !! Just tighten them , also you can get a radiator pressure tester and pump up the pressure and then watch for where the is comming from !! I know Snap-on has them or just about any tool slae may have them !!

 

[Carter]

I got a new pump from NAPA several years ago and used the thin paper gasket that came with the pump when I installed it on my M37 and it also leaked. I removed it and made a new gasket from thicker blue gasket paper and once reinstalled no more leaks. If you used the NAPA supplied thin gasket, try making one with some thicker material and that may stop the leaking problem.

 

[Capt.Marion]

I got a new pump from NAPA several years ago and used the thin paper gasket that came with the pump when I installed it on my M37 and it also leaked. I removed it and made a new gasket from thicker blue gasket paper and once reinstalled no more leaks. If you used the NAPA supplied thin gasket, try making one with some thicker material and that may stop the leaking problem.

He did say that he gooped up his gasket with the Permatex gasket sealant to see if that helped, and it didn't seem to.

I'd dry it off, fire it up and go out in front and watch it and see if you can see where the water originates from. The head gasket idea may be viable, the hoses too...

Can you tell, right know where the leak seems to be coming from? Like a general area?

 

[m109guy]

It might be a bad hose which has a pin-hole leak in it. Once the coolant warms up the hose, it expands and leaks.

Just my 0.02 cents.

 

[Carter]

"He did say that he gooped up his gasket with the Permatex gasket sealant to see if that helped, and it didn't seem to.


Capt. Marion;
I read what was posted, but rather than fill my reply post with " it might be this" or "it could be that " responses , I answered from personal experience with what had caused a leak at my newly replaced NAPA rebuilt pump.

 

[SasquatchSanta]

This is a big of a long shot but does the engine have the original head on it?

The stock M37 head is flat across the front vertical plane (edge or end).

The heads on civilian engines have a bump of protrusion on the front of the head. This is to allow for an integral water pump bypass. The reason the M37 dossn't have this "bump" on the front of the head is because the M37 water pump has a bypass hose coming out the top of the pump.

"If" somewhere along the line, someone put a civilian head on your M37 engine it will leak unless a bypass hole in the civilian head was plugged.

I ran across this problem last fall with the Pumpkin Project when I installed a civilian head on an M37. We had to take it off and tap a plug into the bypass hole.

Like I said, this is a long sot but was old as these trucks are --- anything can happen.

 

[citizensoldier]

Very good point Ernie... I am not trying to argue in anyway but I have seen both military and civilian heads and motors both ways? I think its more of a year they were produced than a military civilian application. It could have the wrong head, or head gasket installed but I bet your onto something here..

 

[Capt.Marion]

My apologies, Carter, didn't mean to jump all over you about that.

@ Sasquatch: That's pretty interesting, never woulda thought that there'd be a difference like that. Did that prompt any change in head gasket design? Or would it need to?

 

[citizensoldier]

Yes capt. Two different head gaskets If I can make out to the shop I will take pictures. Does yours have a hump on the front of the head? It is off to the passenger side.

 

[Capt.Marion]

Doesn't seem to, based on pictures. Later I'll trek out to the barn and take a peak. Mine's a '62 block, I'd assume the head is the same.

Would there be any changes in the markings on the top of the head?


Sorry for the massive thread hijack, Irv, but I'm intrigued...

 

[Texjun]

Sir

Could I trouble you for a picture of the Hump on the Head of the 230 Engine in the M37.

I don't think mine has a hump but I would like to make sure.

I am getting ready to order full gasket set from NAPA.

Thanks in advance