wetwhistle

So I did a top end refresh on my 500 efi (valve springs and head gaskets). I have put 6 hours on it since then. Everything was flawless until last weekend when it stared running warm.

If I run it wot for more than 20 seconds the temp starts to climb and will continue to climb unless I back out. 180 degrees plus.

I can run it all day long around 3500 rpm and it stays right at 155 degrees. Then when I bring it off plane into a no wake zone the temp will actually drop to about 140-145.

Today I took a look at the sea water pump and it was perfect except for minor scuffs on the housing. Nothing excessive I replaced the impeller but not the housing. I also replaced the thermostat just in case. It appeared to be just fine and I did a boil test on it and it started opening right at 140 and was pretty well open at 170. So it has me wondering if that is the issue.

I haven't ran the boat yet and won't be able to until Sunday. It now has me wondering if that is the problem since it seemed to check out ok.

Has anyone had is issue before? Any help would be great!

wetwhistle

Any Ideas?

Airpacker

Possible restriction in the hose or passageway between the helmet and the transom plate due to corrosion. You apparently have enough cooling at lesser demand loads and insufficient cooling as the heat load demand increases.

Unfortunately, not an easy one to verify.