ZR6 over heating

[KonaKing]

I have a 2004 22v with a ZR6 in it. It has a closed looped cooling system so I run antifreeze in the motor and and use raw water/lake water to cool the antifreeze through a heat exchanger. Lately It has been running hot so I checked the impeller which was good. So my next step was to check all my hoses/ I flushed both the raw water and closed system completely except for the heater core. Replaced the t stat and put it all back together, ran it in the driveway and it ran at 160 t0 170 with plenty of water dumping out the exhaust both sides.

Put it back on the lake yesterday and as soon as I got up to speed it heated up again. At an idle or lower rpm it will cool right off. The risers never felt hot but the gauge was reading hot and seemed to be functioning even though the motor did not seem that hot. It did not purge antifreeze. but it still makes me nervous. Does anyone else run this motor and have you had any trouble cooling it or problems with the temp gauge or sending unit.

Thanks

[mcd]

Eventhough you checked the impeller, I would still replace it. It's the first weak link in the cooling system. They can be worn out and still look intact.

[chpthril]

Definitely sounds like a lack of circulation. Either coolant through the block or raw water through the heat exchanger. My gut says that the heat exchanger has something like lime deposits, etc built up in the fins. This would allow enough raw water to pass at idle/low speed, to keep the engine cool, but at higher engine speeds, it's not enough. The other would be the circulation pump, but I would see about pulling the heat exchanger first, and inspecting it for a restriction on the water side.

[KonaKing]

ok pulled the heat exchanger out tonight and there was rubber from the old impeller but most of the tubes were clean and no sign of build or sediment. Possibly the water pump ???? When I was on the lake the exhaust riser never got hot and the manifold were cool also. This tells me the raw water is cooling well and the fresh water is not. I am going to take it this weekend and a temp probe into the de-gas bottle and read the temp there to rule out a sending unit before I go onto the water pump.

[KonaKing]

sending unit is bad. Gauge was reading over 200 f and my temp on my fluke was showing 162f which is what my t-stat is. So that will get changed Monday.

[JUST-IN-TIME]

don't you like the t-stat is under the heat exchanger?

all marine motors are like this

back flush the system always

[KonaKing]

don't you like the t-stat is under the heat exchanger?

all marine motors are like this

back flush the system always

Not the PCM ZR6 everything is at the front where it should be and heat exchanger is at the back. Check out SPBFAN's pics.
Anyways replaced the ET sending unit not the ECT sensor and all is well again.