The Stovebolt Site Forums The Shop Area Engine Shop mysterious coolant leak

1952 1/2 ton Chevy, 1954 235 engine. Here's the problem: truck will overheat after a few hours on the road due to lack of coolant. I know this because I'll stop, open up the radiator and add about a gallon every day or so. But there are absolutely no signs of coolant leaking- checked hoses, heater, drain cocks, everything. This leads me to conclude that coolant is somehow leaking inside the engine/head. The oil is not showing any signs of water, however. Has anyone ever heard of/ seen this, and if it's true, is there anything I can do to fix it short of pulling the head? Thanks brothers,

Tyler

Tyler Watts,

I have heard of this. One would have to assume if there were not external signs of a leak that the coolant was being burned in one of the cylinders. I think if the head gasket did leak, that when the rig was shut off and the cooling system remained pressurized that it would push coolant into the cylinder and it would become quite evident there was a problem

Another thought would be that the leak doesn't start until the rig is running down the road at operating temperature...then, the leak starts to dribble, but you can't see evidence of it because it is windblown away. Sometimes water pumps will leak only when running and under a slight pressure. Take a close look under the truck for signs of rusty coolant spray. The area under the fan pulley is a popular spot for the pump seal to leak.

Stuart

Tyler If you were losing coolant into one of the cylinders it would show up in the exhaust, also your plugs would show this as well. If the engine is runing strong and takes a while to overheat your problem is probably not internal. I agree with Stuart, take a good close look at you waterpump, radiator and hose fittings, don't forget to check your heater core. It may be worht your time to have the system pressure checked at a radiator shop. Good luck and let us know what you find.

Agree. It needs to be pressure tested best when cold. I,ve used Bars leak to stop minor head gasket leaks.

u can buy a pressure tester,,,,,goes in top of radiator, pump it up to 14 psi or so n watch what happens.....not sure what they cost new...try napa..

Thanks for the comments. I'll take another look at the water pump, hoses, and heater core. But I'm telling you I've looked hard and can't see any sign of a water leak. It's losing a good gallon of water for every hour/ 2 hours of driving, so I'm thinking I would be able to notice the leak! The theory that it's only leaking at operating temp. while running might be the winner, though, because I have noticed a slight antifreeze smell when driving. I'll let you know what I discover.
Tyler

I've had the same problem with my '94 S-10. I would only lose coolant after warming up. It was a head gasket. It would expand and leak into a cylinder and blow out the exhaust. It took forever to find because it was practically vaporized coming out the exhaust. Solved it by having someone drive behind me at night when there was no crosswind. His low beams when tailgating lit the moisture up.

Sounds like a warped head/blown head gasket, my 2 cents

try a new radiator cap before you do anything and bars stopleak next if that dont work dig deeper

What type of cap is on the radiator, low pressure or high? It sure sounds like a head gasket to me, pull the plugs out and look at the color of all six to see which one is different. Also, try pulling the plugs when the engine is hot right off the road, you may be able to see or smell coolant leaking. Joe

Don't rule out a crack in one of the combustion chambers, often #3. From scanning many past archive here and at VCCA this appears to be a very common problem. As Tuts mentioned earlier, check the plugs, if you are seing a white resdue on one of the plugs it may indicate a water jacket leak.
Denny Graham
Sandwich, IL

The easiest way to check for pressure is to run it hot and release a little pressure from the radiator cap. Be careful and don't scald yourself.

I would check all the plugs. You may find one that looks different than the others. Also, check to see if there is a coating of rust inside the tailpipe. Losing that much into the oil would show up pretty quickly but it could be going out the tail pipe. A crack in the head near one of the exhaust seats could do this.

a internal coolant leak in the cylinder will steam clean the spark plug--it will look like new-
Running the engine hot with the radcap off, look for
bubbles--exhaust compression gases in the coolant.

My 1951 4400 is supposed to have a low pressure cap on it. 4 psi. Is it possible that a higher pressure cap, like the current 15 psi ones, would push water out through the water pump seals, or some place else that isn't designed for that pressure? I'm still a week away from trying to start mine so I'm curious.

Starkweatherr, If everything is in good cond. & you have had the radiator cleaned & checked you could put a 7 lb cap on but I wouldn,t go any higher then that. You can split the radiator or heater core seams if they are not in excellant cond.

Thanks, Wrenchbender Ret. To tell you the truth, I haven't done anything with the radiator. As soon as it stops raining I plan to put some water in it and see if it stays there. Come to think of it, I could just run a funnel out the side of the hood and let the rain fill it. ;}

Update- truck has been running with 16 lb. rad. cap (I have a feeling this ain't proper...). Checked the plugs, all look normal, no sign of steam/ water. I'm running the truck right now with the cap off just to see what happens. So far, it's been idling for about 1/2 hour with no problems. So, should I go to a no-pressure cap? What's going on with the 16 lb. cap? Seems like we're close to solving this- thanks guys.
Tyler

someone just didn't have a clue and used what was handy - should be 7# max as bender sez, but don't put a "no-pressure" one on, use 4-7#

Bill

preasure test the system if no leaks found you can use your air comp to inject preasure into each cyl to do this you will have to get each cyl on TDC or remove the rocker arm *** then remove thermostat and fill to top of therm housing put air in each cyl if you have a bad gskt or crack bubbles will show in cyl that is bad...doc

I had a coolant leak in my Heater core,,,Just a thought. You said you could smell coolant when In the cab

Preasure caps..On The radiator..Everytime I log into this place I learn something new//// I have a 235 55 3/4..my cap is a 14?? Is that incorect? M/G also rebuilt 20,000 ago

A lot of the older radiators were "honeycomb" design, with the coolant passages formed by thin zigzag strips of copper soldered together to form a sort of maze for the coolant to flow through. These were not supposed to be pressurized to more than 7 pounds due to the danger of separating the solder joints. Later model tubular radiators could take much more pressure, up to 12 to 16 lbs or more without damage. If you can see oval-shaped tubes when you look into the top tank of your radiator, you can run the higher-pressure cap. Every pound of pressure on a cooling system raises the boiling point 3 degrees, so a 15-lb. cap will let the coolant hit 250 degrees or more before it boils. A 7-lb. cap would raise the boiling point 21 degrees at sea level, less at higher altitudes.
Jerry

Got it...Thanks..

Since we are on this subject, I have not drove my truck in a long..long time, I have let it run..sometimes for 1/2 hour. I never see much flow in the Radiator,I even turn the heat on,the heat works pretty good,it gets warm in the truck,but 2 things I have noticed...not much flow in the radiator and the return hose from the heater coil never really gets that warm. Is this normal..or should I do a flush.