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Overheating mystery. (again, still)

1988 Astro Van. Well maintained. Began running hot. At speed, temp is normal..stopping at red lights, overheats. A slight aroma of coolant. Changed...water pump, fan clutch, thermostat. Radiator is good, had it taken out, checked for leaks and blockage...none. The radiator cap is good. There is no water in the oil. There is no smell of exhaust in the radiator. In a 25/30 mile trip, I will lose a gallon of fluid. I can never find or see the leak...I don't know where it goes. There is no puddling under vehicle and no trail of fluid that I can find. I can smell a faint aroma of coolant when it starts overheating. Engine still performs well, responsive. Doesn't burn oil or leak oil. Engine and transmission have both been replaced, but long enough ago that this overheating is not connected. ANY IDEAS? My husband says crack in the head, and fluid is vaporizing out. Or possibly a crack in the block (but wouldn't water show up in the oil) We are really puzzled. Plus all the money we have thrown at this problem with no solution. Thanks. Perry
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Perry Templeton
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1988 Astro Van. Began running hot.

At speed, temp is normal..stopping at red lights, overheats. No water in the oil. Faint aroma of coolant when overheating. Water pump, fan clutch, thermostat, radiator & cap all good. Loses a gallon of fluid in 25/30 miles. Don't know where it goes. No puddling under vehicle. No trail of fluid. My husband says crack in the head, and fluid is vaporizing out. Or possibly a crack in the block. ANY IDEAS? Perry. __________________________________________________

Also classic symptoms of failed head gasket.

Borrow radiator pressure tester from auto parts store. Remove radiator cap, screw on tester and pump it up to 16 PSI. Let it sit and watch the pressure gauge. If the pressure bleeds down there is a leak somewhere. If no fluid is seen, then leak is into engine from

1.) failed head gasket, or; 2.) head crack, or; 3.) block crack (least likely)

Coolant aroma is hot coolant vapor boiling up from coolant reservoir.

Good luck.

Wendy & John _____________________________________________

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Wendy & John

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Perry Templeton

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David J and Lynne J Shepherd

On June 17th you mentioned a concern about vacuum leaks (cruise control issue) Now you mention Lost coolant. Could it be possible that you've got a coolant/vacuum leak into (or about) your intake.

There is the possibility of lean burning resulting in higher combustion temperatures (detonation etc) or a burnt coolant mixture affecting your fuel/air mixture. Best to pressure test your system under the "exact" conditions where the problem occurs.

The 3.8 in my Olds 98 had a cracked 90' elbow from the intake that would only leak when the engine was cooling down. Not when hot, not when cold and oddly enough not when warming up. I would lose about

1/2 quart each time, pressure tests cold or hot showed no leak.

I'm thinking the coolant is leaking into the combustion chamber and being burnt, if it's going out the tailpipe as vapour you'll never see it

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Perry Templeton

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