Disappearing coolant leak: Part 2

[Mark F.]

Thanks to all who provided suggestions of where I should look for the disappearning coolant in my '65 small block. After I wrote the post, I got out the I/R gun and did some more checking.

When the car starts, it takes a minute or some to warm up, I guess the car is "clearing its throat". After a minute or so, it runs smoothly.

The I/R gun shows, when the car is warmed up, that cylinders three through eight are running at about 480-495 degrees, measured at the exhaust ports and manifold.

Cylinders 1 and 2 are running at about 375 degrees. Spark plugs are the same for each cyliner (AC-44).

Is the coolant "cooling" the front two cylinders? Are the cylinder heads cracked in the exhaust ports, or are the head gaskets bad? Brand new engine (professionally rebuilt and assembled by a reputable engine shop), 870 block, no overbore, rebuilt 461 heads, 1.94 intake valves, 1.50 exhausts. No porting done to the exhaust ports, etc.

Your comments are, as always, appreciated greatly. I need a winter project, but I'd rather repaint the car than tear the engine down (again!).

Thanks

Mark

[Joe L.]

Re: Disappearing coolant leak: Part 2

Mark-----

I really doubt that the difference in temp readings between the 1 and 2 cylinders has anything to do with coolant leaking into those cylinders. This may or may not be happening, but I doubt that it would have any measurable effect on cylinder temperature. More likely, the difference in temps is related to the normal differences caused by the coolant circulation pattern.

It is possible that the coolant loss that you're experiencing is due to some defect in a major engine component (like a defective head gasket, cracked head, etc.). However, I still think that the most likely cause is just the normal loss through the overflow. If you want to test this theory, rig up a temporary "coolant recovery tank" using a plastic jug into which the overflow hose discharges (instead of to the ground). Make sure that you seal the opening of the jug as best you can except for the tube going into it and make sure that the cooling system is at the "full" level when you begin the test. You can use wire or something to fasten the jug to the frame or whatever is handy. Then, check the jug after driving for awhile and see how much coolant is captured. Compare that amount to the amount you need to add after the same period. Try to position the jug so that the overflow tube is a "straight run" to the jug. If necessary, you might even want to obtain another piece of vinyl tubing from a hardware store and cut it shorter than the original overflow tube. In that way, you can more easily position/fasten the jug and still have a free flow into the jug.

[Clem Z.]

Re: Disappearing coolant leak: Part 2

if coolant is getting into a cylinder it will most likely short out a spark plug,since the coolant will not burn, or the plug in that cylinder will be very clean compared to the others. the best check is to use a tool to pressurize the system and see if it looses pressure over time. it fits on where the rad cap goes and has a hand pump with a pressure gauge to pump up the pressure. most good rad shop have this tool.

[lyndon sharpton]

Re: Disappearing coolant leak: Part 2

check all of your clamps make sure they are tight an not seeping. also you will puke a lot of fluid on a peroid of time. I think that might be what is going on here. on the pre 74 car one should check an top off the tank on a regular bases.

[Michael W.]

Re: Disappearing coolant leak: Part 2

I think you meant pre '73 cars, an not pre '74.

[Patrick H.]

Re: Disappearing coolant leak: Part 2

Not only that, but "topping off" the tank is the #1 cause of coolant loss in pre-73 Corvettes. 98% of people fill them too full. The system then pukes out coolant until it goes down to the proper level. Owners then freak because the cars spewed coolant when in reality it was their mistake that caused the problem.

Patrick

[Clem Z.]

Re: Disappearing coolant leak: Part 2

the external tank should only be 1/2 full cold or if no expansion tank the water level in the side tank rads should be 3" down when filled cold

[Ken Robb]

Re: Disappearing coolant leak: Part 2

As to the cracked head, I had one on a 56 Chev V-8. Crack was between valve holes. Water would drip into the cyclinder when engine cooled off. I would take out the spark plug in morning and have a bit of water in the cylinder. So knew it was the one. Had checked all 8 cylinders to find it. When took off head, the piston top looked like someone had beat on it with a ball pean hammer. Water dropping on the hot piston had erroded away the metal over time. I have also had a clamp not tight and would loose pressure and coolant there. How much are you loosing over what period of time?