Hello, I know my car has a leak. Blok check test confirmed.
Symptoms:
Car overheats after driving for awhile but only intermittently
Overflow is filled almost to top after driving and has wet sides.
Coolant fails to return to engine.
Here is the interesting part. I removed the lid for over flow and took out the hose and exposed it to air. Then I took off rad cap. Instant suction and collapse of both lower and upper hoses. Why did this occur? Bad rad cap and or/ blockage?
It sounds like a head gasket leak. The gasses from the combustion displace the fluid. A quick combustion gas test would prove this out. You need to get it fixed before you toast the engine.
Interesting question. It almost sounds like there’s trapped air at the bottom of the engine somewhere, and by doing what you did, it allows the coolant at the top of the engine to move down to the bottom, and this movement of the coolant somehow creates a vacuum which collapses the two main radiator hoses.
A couple of things you could check. If you remove both upper and lower radiator hoses, does coolant readily move from the top of the radiator and out the bottom? Is the overflow hose clogged with debris of some kind between the overflow tank and the top of the radiator?
A leak in the cooling system (even a tiny one) can prevent coolant from returning to the radiator from the overflow bottle.
As to a head gasket fault I’m always dubious of that until proven wrong. The reason being is that because as a mechanic I’ve seen a lot of cars diagnosed with a bad head gasket (or 2 of them) and in the majority of cases the head gaskets were not the problem.
Intermittent overheating could be caused by a flaky thermostat or erratic cooling fan operation.
There are tests for faulty head gaskets so that should not be a guessing game.
““Then I took off rad cap. Instant suction and collapse of both lower and upper hoses””
I think you may be misinterpreting what occured here… Suction and collapse of the hoses is contradictory. More than likely what you heard was Pressure…which when relieved allowed the Pumped Up and Ballooning hoses to relax and collapse.
Sounds like typical head gasket woes… It will pressurize the coolant system…forcing coolant out into the overflow…AND THEN…the head gasket Breach is leaking air and not allowing the subsequent suction effect of when the hot coolant cools and shrinks in volume. This is what pulls the coolant back into the radiator and when there is an air leak as in Head Gasket failure it will not allow this suction to form.
The head gasket will however allow cylinder compression to leak out into the coolant system…this is an easy thing to achieve with cylinder pressures being what they are. When this happens…well you know the rest. Textbook Head Gasket Failure
Blackbird