Cooling system mystery?

I have a 1992 GMC 3/4 ton Sierra Pick-up 4WD. I have a nasty coolant leak at the rear of the engine. The problem is that there is no way I can see exactly where it is coming from. The heater core, water pump, radiator, and all hoses are fine. The coolant only leaks when the engine is running (cold or hot) even when the system is not under pressure (radiator cap off). I have narrowed it down to somewhere between the pump and thermostat because that would be the only area under pressure. I have tried Barrs Stop leak (2 bottles) and more antifreeze than I care to buy again. It hasnt even slowed it down. There is no coolant in the oil or coming out of the exhaust. I dont think it is a frost plug unless there is one on the back of the engine. The whole engine is dry as far as I can tell. I dont know where it cold possibly be coming from. It drips mainly on the drivers side right above the starter. The higher the engine revs the faster it shoots out, judging by the cloud of steam off the exhaust manifolds. I dont have much money to fix this and I really dont want to start ripping the engine apart to locate it. If I could only see where it was coming from I could fix it. If anyone has ever heard of a leak in this location please help with your ideas. Thankyou all.



Joe Wagner

At first I thought you had the classic intake manifold leak. But you say it actually SHOOTS out! wow, that's pretty bad. But you say you cant see where it's shooting out at. Sounds like something is broken or cracked to me. OUCH! If your not real handy with a wrench I'd get it into a trusted shop asap.

Get a lone/buy a pressure tester. This tool will really help you narrow down the leak. Not much on that side only intake gasket and frost plugs.

Well this morning I was on a mission to figure out where it was coming from so I got a mirror and a flashlight. I started it up to inspect for the leak. By the time I got out of the cab and walked to the front of the truck, it had poured about two gallons of coolant on the floor, before I could see where it was coming from. Now its out of fluid and I still havent found the leak. Fluid all over the firewall and the floor but no trace on the engine. I live in Minnesota and my garage isnt heated so I didnt dare fill it with water. I wasnt about to buy a gallon of coolant just to watch it hit the floor. I took my shop vac and put the hose on the blow side and held it over the radiator opening. Fluid shot out of the Passanger side of the intake manifold near the front of the engine. The whole time it was running right under the lip of the valve cover. It ran to the rear of the engine right off the back leaving every bit of the visable engine dry. At least nothing got in the crank case. I am not looking forwars to changing this gasket but I refuse to pay some shop 60 or so dollars an hour to do it. Thanks for the help guys

check the top heater core hose where it goes to the intake manifold. GM uses a snap fitting and they SUCK on my 94 its back by the dist. I belive some are up front but both on pass, side. there is an "O" ring in there if they are not seated perfectly they will leak. Who ever designed these dam things should be fired.

check the top heater core hose where it goes to the intake manifold. GM uses a snap fitting and they SUCK on my 94 its back by the dist. I belive some are up front but both on pass, side. there is an "O" ring in there if they are not seated perfectly they will leak. Who ever designed these dam things should be fired.


Funny you should say that. I broke that thing trying to unscrew it from the mainfold. I I wish that was what was leaking but it is the manifold gasket IM afraid. And yes that is a engineering wonder on GM's part. Probably costs 100 dollars to replace.

maybe $100 if you do it yourself! I called the dealer on a price for the gasketes, $50 for the pair. That doesnt include ANYTHING else...

Also broke my heater hose coupler & replaced w/
steel one even though I've heard it makes my aluminum the inferior metal & subject to corrosion.
I've only seen a couple comments on this. ?