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Discussion Starter #1
Hello all;

I have a PROX 800 an have an overheating problem. Not airlocked. Thermostat is good, even removed to ensure coolant flow. At lower RPM, I have no problems. However, when I get it continually high-up the RPM range and keep it there, the motor starts overheating, eventually shutting itself down. My biggest concern is that the heat exchangers are cold.

I was told that I may have a bad head gasket, leaking pressure into the coolant, preventing my water pump from properly circulating coolant through the exchangers. Any comments would be helpfull. Thanks...
 

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Hello all;

I have a PROX 800 an have an overheating problem. Not airlocked. Thermostat is good, even removed to ensure coolant flow. At lower RPM, I have no problems. However, when I get it continually high-up the RPM range and keep it there, the motor starts overheating, eventually shutting itself down. My biggest concern is that the heat exchangers are cold.

I was told that I may have a bad head gasket, leaking pressure into the coolant, preventing my water pump from properly circulating coolant through the exchangers. Any comments would be helpfull. Thanks...[/b]
You may have a air bubble in the system may want to burb it.
just a thought this happened to me last season. Good luck Dave
 

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I don't get it. You say it's not airlocked, but you have a hot motor and cool exchangers. That leads to questions. Why do you beleive it's hot, and why do you believe there's no airlock? Is the motor physicaly hot to the touch? Did you bleed the system by raising the front of the sled a couple of feet up, then starting and add anti freeze until it came out the top of the bleeder?

Have you checked to see if the water/oil pump belt is intact?
 

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Discussion Starter #4
The system was bled with nose-up. The motor is very hot to the touch, to the point that thye computer shuts it down. When the machine is warming-up, the exchangers are getting hot. When I put around, the exchangers remain hot. When I go all out (for several minutes), temperature gauge rises, motor starts to sputter, then the computer shuts it down.

Open the hood and the engine compartment is very, very hot. Reach out back and touch the exchangers, and they are cold. Water pump belt has 1500 miles on it. Local mechanic is saying that I may have a pressure leak at the head gasket, dumping pressure into the cooling system. Pressure gets so high, the water pump can no longer circulate the coolant. That make sense to you guys??
 

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<<<I may have a pressure leak at the head gasket, dumping pressure into the cooling system. Pressure gets so high, the water pump can no longer circulate the coolant. That make sense to you guys??>>>

Ummmm, no......

1. Pressure should have nothing to do with the pump's ability to pump anti freeze. What is he thinking? That the the antifreeze thins out under pressure or something? That the pump is trying to pump steam? If it were trying to pump steam, where did all the antifreeze go to make room for that steam? Out the cap with nobody noticing it - or the resulting mess?

2. I can assure you that if it were a head gasket leaking compression into the cooling system, there would be antifreeze overflowing from the reserve bottle - BIG TIME! I was there with that exact problem on a Polaris quad this summer. Took me 3 tries to figure out the PO had overtorqued the head bolts and warped the cylinder.

If it was leaking the other way - from the cooling system into the motor, you should see some awesome clean spark plugs, and a distinct anti freeze smell coming from the exhaust - along with much more steam than normal?

You mentioned somewhere that your sleds cooling system had been pressure checked? If that's the case and it checked out OK, why the thoughts regarding a blown head gasket? Wouldn't that have shown up on the pressure test that wouldn't hold?

Is there a chance that the antifreeze is going through the coolers so quickly there is no time to dissipate any heat in them - because the t'stat has been removed? That's been noted before. I can remember having that problem with a car when I was a kid - for the same reason.

Are you running 100% antifreeze? I've seen sleds have trouble overheating because of that. It HAS to be mixed with water.

If you've been through the above, and you are absolutely sure there is no air in that system, because YOU saw it was bled using the proper nose high procedure, then the impeller idea, or some other water pump related mechanical issue, may have some merit. Just me.
 

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You have air in your system and/or your thermostate is stuck closed.
The only other thing it could be is the pump itself and/or a leak.

keep burping the system and look for a leak.
 

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I had this issue with a polaris 700, the nut that held the water pump impeller on was loose and eventually fell off (that way from the factory). It would run great at idle, NO air in system, and you could feel the heat going to the back, but once you opened it up, it would overheat big time. It wasn't moving fluid.

If it's full of coolant, no head leaks, and the water pump belt is good, check the impeller!
 

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Discussion Starter #8
I was kinda doubtfull of the head gasket deal myself. I'll remove the waterpump and check the impeller. That's all I can think of. Everything else checks out. I'll let you know. Thanks for the input, much appreciated...
 

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good luck, i went through 3 cylinders and 6 pistons before I finally figured it out. You would think a NEW engine would be put together right!
 

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Thermostat is good, even removed to ensure coolant flow. [/b]

I was thinking impeller too.

Or, could it be some kind of blockage that lets enough coolant through at lower engine rpms/temperatures? Is the system absolutely clean; no old "stuff" in there, mixed coolants types, etc?
 

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I had this issue with a polaris 700, the nut that held the water pump impeller on was loose and eventually fell off (that way from the factory). It would run great at idle, NO air in system, and you could feel the heat going to the back, but once you opened it up, it would overheat big time. It wasn't moving fluid.

If it's full of coolant, no head leaks, and the water pump belt is good, check the impeller![/b]

Tis is not an uncommon issue. I replaced a water pump impeller in an 800 Switcher just this week because it had come loose and rounded out the 2 flats where it touches the shaft. I've also seen a few where all the vanes wore off the impeller leaving just the center hub on the shaft. A sled that seems fine at low speeds but heats up when pushed is a great sign of a slipping impeller.
 

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Discussion Starter #13
I'm definately checking the impeller. In my opinion, it's the only possibility. Thermostat is good as I submerged it in water and brought it to a boil. It opened just before the water began to boil. Belt has 15oo miles on it. With the housing apart, I'll check it to see if it's within the limit. Thanks again to all for the help. I'll lose that shop's phone number...
 
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