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losing coolant???

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Nick Shurtleff

New member
I have a mercruiser chev 350 . So I've been loosing coolant from my heat exchanger for a while now and can't figure it out... I have replaced the riser gaskets and today I took the heat exchanger out and pressure tested it seperatly and it held 20 psi all day long.I even heated it up to about 140°, no leaks. Could my new gaskets not be sealing? I run my boat for about two hours and it will over heat and be low on coolant and I fill it and it will be gone in 5 min running 3200 rpm but if I'm idleing it seems to stay full?
 
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The only way to really find out if you have a leak is to buy or borrow a radiator pressure checker.

It should connect to the coolant tank at the input location where the cap is.

Pump it up to the pressure stated on the cap and look for leaks.
 
In my case the Heat Exchanger was bad, mixing the coolant with the raw water and sending it out the exhaust. Sea Kamp makes a good one.
 
At first I thought it was the heat exchanger too, that's why I took it off and took it to work. Hot tanked it and pressure tested it. I couldn't get it to leak at 30 psi! But after running my boat the day it was losing coolant I blew into the heat exchanger and coolant came out the raw water end caps
 
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