www.iFourWinns.com

Just wondering... When the engine comes up to operating range, the temperature gauge fluctuates somewhere around 10 to 15 degrees. When underway it runs about 170 or so, then it climbs to 180/185 (hard to tell exactly), then the stat opens and the gauge goes back to 170. It does it all day long, and it's very consistent, no matter the speed or rpm. My question is, should it move that much? My only frame of reference is my truck. When it's up to operating temperature it's pinned on one temperature all the time, very little to no fluctuation in temp. The only info you might want to know is that it's on a lake in northern Wisconsin, and I bet the water was about 45 degrees or so, when this happened. Also, new impeller and stat. Opinions appreciated. Thanks.

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Mac
2007 Four Winns Horizon 190

I have a 98 that would do similar things, same motor , much larger variation in the gauge in my case, like 50 degrees. In my case cruising on plane is when it would start to wander.

I *did* find a small blockage in the thermostat housing, common issue apparently when an impellor lets go small bits of rubber get hung up in one of the smallest passages of the housing, coat hanger or similar cleared it out for me. I also had a bad ground somewhere that was causing multiple problems with the gauge panel. After cleaning all connections thoroughly and clearing that passage it will get up to temp and stay rock solid until coming back to idle depending on water temperature. a cheap IR temp gun will help confirm what temps are throughout the engine as well.

others I am sure will have a better explanation.

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Jon Miller
1998 four Winns Horizon H200
Volvo Penta 4.3 GL
Newtown, CT

untitled-545 by millerjont, on Flickr

I have found that the OE Volvo/OMC style stats start to open at about 155-160 tested in a pot of hot water and should be fully open at about 170. The dash gauge can be off, usually on mine it reads a bit higher than what I get on the engine. I have found that the hottest place, is the intake manifold right underneath the thermo housing. Get an IR temp gun and take readings there after the engine has warmed up. On the dash gauge, when all is right with the cooling system, mine runs at 160* at idle. It will rise to about 175 after coming off plane, but then after running at idle speed for a few minutes it will drop back down to 165-160. I do not think that with a 160 stat you should be seeing temps of over 180, unless the gauge is reading high (they work on resistance, corrosion in the wiring can affect it.

Sounds like your stat may be a bit slow to open....

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

Ended up buying a new stat (Volvo OEM), and had my mechanic install it. Fixed the problem, the gauge is now rock solid with very little movement. The old stat was working, in the sense it was keeping the engine from overheating, but it was not working as it should have. As I said above, the temp gauge was wandering 15 or more degrees on the old stat. Glad to have this done, one less thing to worry about.

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Mac
2007 Four Winns Horizon 190