Hi guys.
Recently purchased a 2003 heat with 525sc. Love the boat already put about 15 hours on it. Having trouble with closed cooling system. I found that anything over 4000 rpm the coolant resevoir fills up with coolant and over flows out the cap and into the bilge. Ran approx 20 miles sunday under 4000 rpm and never lost a bit of coolant. Heres what I've tried. Back flushed complete raw water side with new impellor and housing, removed heat exchanger and end caps. cleaned heat exchanger and replaced all gaskets, same with oil cooler, flushed ps cooler and fuel cooler. No change. Removed fresh water hoses from heat exchanger and pressure tested. Held pressure overnight. Perfomred a block test with a chemical that changes colors with any exhaust gas in coolant. No change in color. Motor has a little over 400 hours on it and was gone threw at 400hrs by previous owner. Heads and block were pressure tested.
Running out of ideas and any help would be great.
Thanks

What size tstate you running ?

I think its a 120. Temp never gets above 150 until all coolant blows out the cap and then starts to overheat.

Probably need more details on you motor set up. But I would think you should be running a 140 or 160 tstat.

Running a 3.3 whipple installed in 2004. Still running piggy back computer from whipple I'm thinking before they had the capabilities of reprogramming factory ECM. Whipple has a water cooled intercooler teed in between fuel cooler and ps cooler. Coolant side does have a reciculating pump.

maybe have the heat exchanger pressure tested by a radiator shop? maybe it's fine until it warms up AND you get enough water pressure from the raw water pump and it's over pressurizing the engine coolant.

also, just incase your block pressure test didn't show what it was supposed to, do a leakdown test on the motor, could be a blown head gasket over pressurizing the engine coolant also.

both complete shot in the dark, but maybe?

Where would you find if Felpro head gasket #1075 is the correct gasket for 2003 525 serial #om900680. Just wondering if they have the correct coolant passages.

Dustin is that you? If that is you I want a ride in this thing when you get it all worked out. I saw it out on the river a few weeks ago and somebody said it might be you and your new boat.

Yeah its Dustin. We will be hangin out around Diamond Island Saturday. If your out we can go for a ride, just not fast for too long. Still pretty impressive. Lol