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AQ145a expansion tank leak at operating temp

n36511

n36511

Regular Contributor
All,

I have been chasing this issue for some time and still do not know the issue. I have a AQ145a that has a slow leak from the expansion tank. It only leaks when the engine reaches operating temp. I have removed the cap when running and there are no bubbles or oil sheen in the expansion tank so I dont think it is a head gasket problem. If it was a head gasket, would it not leak from the time the engine cranked instead of waiting to reach operating temp? It eventually leaks enough to make the engine temp raise. Any thoughts on next steps to take? Or things to check? I have replaced the radiator cap 3 times.
 
Pressure-test the cooling system and see what happens. If it looses pressure, my guess would be a head gastket problem, but it could also be a cracked/warped head.
 
I just called AZ and they rent the pressure test gear so I will try to test next weekend. One other question..... If I open the cap while the engine is running at normal operating temp, is any coolant supposed to come out? With the cap on, there is just a little drip from the cap while running at oper temp. If I remove the cap (carefully) the coolant doesnt spew out, only comes out at the same little drip rate. I have always thought that it would not come out while the engine was running, but as you can tell from my posts, I know little about this stuff.
 
There shouldn't be any coolant coming out under normal conditions.

Also, there are two other possibilities you may want to check.

1) How is the rim on the top of the tank's filler neck where the cap is sealing? If it is bent or somehow deformed, you won't get the new caps to seal.

2) If the heat exchanger is perforated, you may be getting raw water into the closed cooling system, especially if the exhaust manifold is scaled-up. Of course, a pressure test of the cooling system will reveal that.
 
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