www.iFourWinns.com

Hello all, installed new power steering cooler today and ran for thirty minutes and no leaks all around motor. GOOD DAY. But now a new question arises, it seems the thermostat/ temp gauge is not working. When you turn the ignition on, the gauge jumps to just under 100, so the gauge has power, but it wont climb. After thirty minutes it hasnt moved at all. How do you go about checking the thermostat to see if its bad? Is it like a car? Also, when I tried to take it off I couldnt. Is it just the two bolts holding it in? I didnt want to try and pry it out unless I need to. Let me know... Ryan

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1990 Horizon 200
5.7L OMC Cobra 260HP

It's pretty much like a car, except there's an extra o-ring seal inside. Even if the 'stat was stuck open I'd expect you to have some climb after 30 minutes. Makes me wonder if your temp sensor is bad, or if the connection there is corroded.

I can't remember if you changed the impeller since you've had the boat, but at the age of 20 years it might not be a bad idea to just change the impeller, 'stat, and sensor.

"Overkill Mike"

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Mike
2005 Four Winns 230/240
VP 5.7GXi/DP
1998 F-150 XLT
Boat Pic

Where is all that at?

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1990 Horizon 200
5.7L OMC Cobra 260HP

The style of thermostat that OMC used (and some Volvos too during and after the joint venture years) is actually inside the thermo housing itself not on the opening in the intake manifold as you would see on an auto application for the same engine. Remove the upper hose....raw water intake hose...and manifold hoses from the thermo housing. Remove the 2 bolts that hold the housing on. You may have to tap it with a rubber mallet to get it to come loose. Take the housing and flip it over after removing the bolts and look inside...the thermostat will be right there but held in with a rubber ring...you pry out the rubber ring with a small screwdriver and remove the stat...then you can test it in a pot of boiling water...I have an old style thermo testing thermometer and my OMC stats usually open at 160 or so like they should...sometimes a piece of rust fron the engine or intake manifold will lodge in the stat and keep it from closing all the way...then if you let the engine idle...it will never go above 120*...unless you run it on plane then it will get up to 160 but as soon as you slow down it will drop to 120-100 again...check out this link....

http://www.dougrussell.com/partscatalog ... 18,819,820

When reinstalling I coat both sides of the housing gasket with OMC gasket sealer (or Permatex Aviation Sealer) and also the threads on the bolts..if you do this it comes apart easy the next time because the sealer never hardens and prevents corrosion.....and here in salt water we KNOW about corrosion....

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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

Just an FYI to others, my '04 5.7Gi has the thermostat and housing that LouC described.

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2007 358 T-5.7GXi IB
Previous Boats
'08 H240, '08 V318, '04 268, '04 225

Ryan,

To me it sounds like the temperature sender is stuffed, or possibly the gauge itself. Easiest way to isolate is pull the wire off the temp sensor and the gauge should drop to zero if the sender is the problem. Touch the wire to ground and the gauge should leap up to maximum. If it still sits at 100, then it is the gauge.

It is not going to be the thermostat at this stage as the motor has not even started! Although, as other suggest, you may want to check and relace it at some stage.

Temp sender can be installed in a number of places on a small block chev - it can be in a head, the thermostat housing, the intake manifold, etc. - I have seen them everywhere!

Hope this helps
Alec

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Alec

2006 Horizon 190
VP 4.3GL/SX, Sunsport

I'm just so thankful I decided to have closed cooling, so with boating in salt water corrosion of the engine is one thing less I have to worry about.

Graham

We have had the engine started and ran three times for over thirty minutes with the ears on. Have not had a chance to take it out and ran at full throttle or anything though..

Today we played with the thermo wires at the gauge and wiggled a little while the engine ran with the ears on. We began to see a climb on the gauge to around 120-125, which was great to see. But then after about 10 more minutes the gauge just slowly kept back down to 100 and stayed there.

Today we also took the thermostat housing off and saw the stat in there and couldnt figure out at all how to get it out. How can you tell if its the sensor? Just take it out and put it in hot water?

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1990 Horizon 200
5.7L OMC Cobra 260HP

Sounds more like your thermostat to me. But I still say, if you don't know when your impeller was last replaced you should do it.

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Mike
2005 Four Winns 230/240
VP 5.7GXi/DP
1998 F-150 XLT
Boat Pic

There is a rubber ring that holds it in....there's a groove in the neck of the thermo housing and the ring fits in there...most times there is so much rust there you can't see the rubber ring...so take a small screwdriver and try to pry out the ring...

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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

Yea.. after all the advice we are going to go ahead and replace stat, sensor and impeller. Where is the impeller located at exactly?

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1990 Horizon 200
5.7L OMC Cobra 260HP

In the upper gear housing...under a plastic cover held on by 3 bolts...very easy job...I replace the impeller...wear plate ....gaskets....and housing once a season....they still look good though so they'd probably be good for at least 2 if not 3 seasons as long as you didnt' ground it and suck up sand....

http://www.dougrussell.com/partscatalog ... 18,819,820

just make sure you get the housing gasket in right....

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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

Replaced stat and impeller. Our stat was stuck open. The boat now runs between 140-150 degrees. Is this good operating temperature? Also, how long should it take to raise up to that temp? It seemed like we only had to run it for a few minutes and it was that warm. Then, how long until the temp should drop back to 100 after sitting? This may be difficult to answer

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1990 Horizon 200
5.7L OMC Cobra 260HP

Sounds about right to me. I would've guessed 160F at full operating temp but any gauge can be off 10F. What's the temp rating of the new thermostat?

As far as rise and fall times, I think boats vary with age, engine size, amount of water flow, etc. Mine seems to take a few minutes before it begins to rise, but then rises quickly to operating temp. I've never checked the fall time.

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Mike
2005 Four Winns 230/240
VP 5.7GXi/DP
1998 F-150 XLT
Boat Pic

Mine has always run at 160 as long as the thermostat was not sticking...the difference could be the gauge or sending unit but as long as it's warming up to that level it's probably fine....

_________________
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