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Discussion Starter #1
So I have a 98 500 sportsman overheating. The fan and sensor both work, so it's down to the thermostat or water pump in my opinion. I did notice that the hose from the radiator on the left side is very hot to the touch, while the other (return?) is warm, but not overly hot. Thoughts?
 

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Discussion Starter #3 (Edited)
So i replaced the thermostat....still have a problem. The fan switch/sensor is new, the fan works, no leaks anywhere, new thermostat, and the guy I bought it from says the head gasket was replaced not that long ago. Here's what is happening.

Fluids topped off and I set out to ride. Within about 20-30 minutes of normal use, the temp light comes on and anti freeze is being pushed out from overflow tank. I accelerate and the light goes away (guessing by pushing cooler air?). As soon as I slow down, it happens again. I can normally accelerate one more time to get the light to go off before the light comes on and stays on after slowing down. I pull over, and find that my radiator is down about a half a liter (12-20 oz) of coolant. I fill it up, and all is good until 20-30 minutes and it does it all over again.

Is is the radiator cap/pressure problem? Could it be a head gasket again? Water pump (no noise)? Again, the only place i'm losing coolant is out of the overflow. Higher speeds (35mph +) keep me cool, but as soon as i slow down or stop for a second, the temp guage pops back on. And all the while i'm pissing coolant.

Any other thoughts? Thanks.
 

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Make sure radiator is very clean thru all fins.
Test only. Pull thermastate. And start up.take Radiator cap off and watch if you can see coolant.moving.if none moving water pump.
Another possible cause could be the radiator is restricted internally. Flush it.
 

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Sounds like a bad cap.

Auto parts store should have a tester for the radiator cap. I think it is a 13 psi cap (if I remember right). Or you can just buy a new one to eliminate it as a possible cause. They are not expensive.

Sean
 

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You may have air in the system.To remove it raise the front of the atv with a jack or ramps,remove radiator cap and run the engine til the coolent starts to move,shut of engine and let it cool down you should here a burping sound.Fill it with coolent and keep doing this process until you can't add anymore fluid.
 

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Discussion Starter #11
The fins are definitely clean, and I checked for air in the system but there wasn't any. As it was running and I had the cap off, I didn't notice any movement in the fluid. But i also have a concern about the fan. It doesn't turn on until the temp light comes on. Fan sensor and a block in the coolant system somewhere?

And yes, the had gasket has been replaced.
 

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wery7 why was the head gasket replaced? The reason I asked about the head gasket being replaced was because there had to be a why. Is the over heating a new problem or an old one that is on going.

I do not know the logic on your fan that should be in the factory shop manual but on our 325 with only the oil cooler the fan should come on at about 260F and if the light comes one it indicates the oil temp has reached 300F which is too hot for motor oil unless it is like Mobil Racing oil or something equal.

It would be my guess your fan should be coming on well before the red light but only your shop manual or someone with that info could address the fan/light issue.

If it was mine I would back flush the radiator with hot water but I would keep the pressure below 20 PSI and put an old white undershirt, etc over the normal inlet side and see if crude comes out or take it to a radiator shop and see if they will check it out as to Flow Rate.

The return line should be quite hot if the coolant is boiling. If the inlet hose is really hot then your thermostat would have to be open it would seem.

Again we need you to share why the head gasket was replaced.

Do you have a cheap IR temperature gun or can borrow one to shot temp of water going in and coming out of radiator. If you have the radiator shield off you can shot the temp of different spots on the radiator. If you find relative cool spots you can bet that area is stopped up. There are some cheap radiators on Ebay sometimes.

Have you yet physically pulled the radiator off and held it in your hand?
 

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ive read that the temp lite on the 800's comes on at (215-220)deg F.
 
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