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New radiator cap...still leaky

n36511

Regular Contributor
I am revisiting an issue that I have been ignoring for a little while. One of my engines (VP AQ145a) has a bad habit of leaking coolant out of the radiator cap. I have replaced the cap with one from VP but still have the leak. The leak is just a small steady stream of drops from the moment the engine is cranked. As the engine gets warmer I can't tell that it gets any worse. Once the coolant level drops to a certain point, it appears to stop leaking (not for sure about this but thought I would add in the event it helps diagnoise). I had someone tell me I need to do a leak down test but I am not really sure what that is. Do any of you agree or is there something simple I can do to possibly fix this?

As always - Thanks!
 
Does your H/E have a coolant recovery system?
Is the pressure cap a double seal type cap?
Is the seal surface on the heat exchanger in pristine condition?

The outer seal surface must be good in order for the coolant to expand into the recovery bottle.
In order for the coolant to return (as it cools and undergoes negative pressure)...., the seal must also be good!

You mention; "The leak is just a small steady stream of drops from the moment the engine is cranked."
Could you have a head gasket that is allowing for a pressure build within the engine's coolant system?

.
 
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Thanks for the quick reply. I do not have the recovery system. The cap is a new cap with a rubber/metal seal at the bottom of the spring. Where that rubber seal meets the radiator is smooth. The rim of the radiator where the cap screws down is pitted and I thought this may be an issue but not sure at what point the coolant gets past the rubber seal. Honestly I thought I would be able to open the cap while the engine was running (misguided I am sure) without coolant coming out. From what I have read about head gaskets and cracked cylinders, I got a little concerned since the fluid starts leaking as soon as I crank the engine (Hot or cold).

Thanks for the quick reply.
 
Made it back to the boat last night and removed the radiator cap and cranked the engine a few times. The fluid did not pulse nor were there bubbles or oil in the radiator. I did notice a small pit in the metal around the rim of the radiator where the rubber seals the cap that I had not notice before. I may end up just replacing the heat exchanger to see if that clears things up.
 
a good radiator shop can replace the filler neck on the HX....may want to consider that option vs the whole HX.

In addition to the gasket sealing surface, the filler neck also has to be true (not cocked or bent) and the "ramps" need to be uniform so the clamping force applied to the cap is uniform.
 
Agree with Mark!

BTW, what you are referring to is your "Heat Exchanger"..... Radiators are in cars/trucks.
Just a kind heads up on that! :)
 
Thanks Mark. I will check with some of the local shops.

Rick - Thanks for the correction. I realized that shortly after I posted. I went looking for a "aq145a radiator" on the internet and kept getting back "heat exchanger" results :) .
 
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