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Air Leak?


drkyle96

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Car

1994 Honda Del Sol Si; 127k miles; 5 speed

 

Symptoms

With the engine running, I observed a slow stream of air bubbles coming through the tube in the coolant reservoir.

Increasing the RPM does not increase the flow of bubbles, while the radiator cap is securely on.

I first it noticed while flushing the coolant. I had refilled with water and left the cap off. In this case, the air bubble purge

rate was dependent on the engine RPM. It smelled like exhaust gas. The CEL is not on.

 

Pertinent related info

My first thought was a head gasket leak, but...

1) I checked the cylinder compression; all cylinders were acceptable and within 5% of each other.

2) There is NO water in the oil; the oil is not like chocolate milk.

3) There is NO white smoke coming out of the tail pipe and it doesn't smell sweet.

4) There is no loss of power, especially under hard acceleration and high RPMs.

 

When I first purchased the car, I found the coolant reservoir filled with a black gunk. I have had to clean it out a couple

of times since. The gunk could be oil, though it doesn't behave like oil. It doesn't float on top of the water. It sticks to

the sides of the plastic in the reservoir. I also checked the other radiator hoses and found all of them completely clean

on the inside and around the fittings. I also do not observe any gunk in the radiator itself or in the thermostat

housing. It seems as though the gunk is being formed in the coolant reservoir.

 

Any suggestions would be most appreciated.

 

Thanks.

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check radiator

 

my overflow had bubbles as well.. turns out a bracket punched a hole in some of the fins of the rad. and it was leaking.. but only leaking into the tray on the bottom and you couldnt see it leaking

 

black crap could be some stop leak they tried to put in

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certainly no experience on this before. when you flushed the coolant was there much in the way of contaminants?

 

No, there were no contaminants, but the solution was dilute like someone kept replacing with water instead of 50/50.

 

check radiator

 

my overflow had bubbles as well.. turns out a bracket punched a hole in some of the fins of the rad. and it was leaking.. but only leaking into the tray on the bottom and you couldnt see it leaking

 

black crap could be some stop leak they tried to put in

 

Thanks Sarah. I'll take a look tonight.

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  • 4 months later...

Conclusion:

 

The air leak was the result of a small leak in the head gasket. The head gasket was

missing the black material between the cylinders and the water holes in the engine

block and head areas. The black material (on the gasket) was completely intact

between the oil-water and cylinder-oil regions.

 

After replacing the head gasket, the air bubbles were no longer

present in the overflow reservoir. I did some additional research and also learned

what the black gunk in the overflow was and where it came from. The black gunk

was not oil. It was coolant that decomposed due to high temp carbon monoxide.

The CO is slightly acidic and at high temperatures it will react with the glycol.

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