Engine expansion tank overflows

[ronbo1]

It's a bit of a mystery...
Westerbeke 82B with 1500 hours, well maintained.

The engine expansion tank fills to the brim after I run it. I've removed about 3 liters and it keeps filling. I naturally assumed it was a problem with the heat exchanger but a coolant pressure test to 14psi shows no drop in pressure.

Perhaps when the HE is at temp a slight leak allows raw seawater to leak into the coolant system. The head gasket seems OK as there are no bubbles in the tank.

I replaced the 2 pressure caps. My next step is to test the coolant for proper ratio, 50-50. If low, I'll then pull the HE and have it checked or replace it.

I can't think of any other possibility?

Ronbo

[Waltthesalt]

Well whatever's leaking into it has a higher pressure. Do you have a hot water system? Maybe that heat exchanger is leaking but it should show up on the pressure test. Maybe do a pressure test on the raw water side... though hull valve leakage might show a non-existent problem.

[leftbrainstuff]

That's a brain teaser.

If your fresh water side is filling what is draining?

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[ronbo1]

Tested the coolant for proper antifreeze ratio.
It was very diluted with (sea)water.
The heat exchanger will be pulled and replaced.
It will be interesting doing an autopsy on it as the 'experts', too, are baffled.

[Lepke]

If your expansion tank is overflowing after previously removing excess water and there is no sign of oil, it's raw water. Probably from the heat exchanger. Normally the only place the 2 waters are in close proximity.

[ronbo1]

Originally Posted by Lepke

If your expansion tank is overflowing after previously removing excess water and there is no sign of oil, it's raw water. Probably from the heat exchanger. Normally the only place the 2 waters are in close proximity.

You're right. My first thought, so I did a coolant pressure test which showed no leak at 14psi. Ordered a new HE.

[Badsanta]

They can be fixed. Maybe just a bad oh ring