FWC 7.4 Heat Exchanger Expansion Tank Overflows

[ippa2]

Hi,

I have 1997 7.4 FWC Mercs. I've owened the boat a bit over a month and I continually notice that the expansion tank for the heat exchanger seems to always fill up. I will then drain about 1/2 the expansion tank down and run the boat for an hour or two and it's filled up again.

I'm suspecting that salt water must be entering the fresh water cooling system at some point. Are there any commons areas this may happen? Are there any easy ways to confirm this???

The block has apprx 325 hours on it.

I appreciate any feedback on this, as I'm stumped...

 

[Redhook98]

It could only be happening in the heat exchanger or at the joint where your exhaust manifold meets your riser. Check em both out. Have a pressure check done on your heat exchanger and replace the gaskets/block-off plate on your manifold/riser.

 

[rcknecht]

Heat exchanger is the obvious place to look...

 

[fc3]

Pressure check the cooling system.

 

[cruiser]

I had the same symptoms back in July. Pressure tested and it was a leaking HE. No other symtoms other than overflowing expansion bottle..When I took almost a gallon out, I figured something must be wrong.

 

[ippa2]

Thanks for the info. I'll pressure check the HE for sure. In the meantime, how bad is it to run in this condition? I'll be sure to flush out the fresh water system in a month when I haul the boat, but I was going to wait until the season was over to replace the HE... bad idea?