Too Hot HO

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Dear Motorhead,

I own a 2004 Ski-Doo MXZ 800 HO which has been experiencing an over-heating problem. The problem occures even under extreme conditions ie -25 to -40c temps.

I have had the thermostate checked and it appears to be working fine. I have also changed it twice and the service guy says he cannot explain it.

Can you help?



Thanks for your email!

You did not indicate under what conditions the overheating has been occurring. There are situations where – regardless of any malfunction in the sled’s cooling system – a snowmobile will still overheat – even at very low ambient temperatures.

Is the overheating occurring when the sled is ridden on trails and in untramped snow or is it overheating when you’re covering icy, hardpack snow or bare ice on lakes? If it’s the latter, get a set of ice scrapers to help loosen up snow and ice to be thrown on the coolers.

If there is adequate snow hitting the tunnel coolers and the overheating is still happening then you need to check and ensure a couple things beyond the thermostat.

Have you had the cooling system bled each time the t-stat has been changed or checked? If not, you quite likely have an air lock and the cooling system needs to “burp”. You can verify this by starting the sled up in your shop and letting it idle. Feel the coolers all the way to the back and verify they become evenly warm – all the way from the front to the back – on both sides – after idling for a few minutes.

If the coolers are not evenly warm then you have an airlock. There a couple ways to fix this. First, the thermostat housing has an air “bleed” screw in it. Loosen it and let the sled sit overnight. Tighten it, top up the coolant thru the cap and reservoir and then try the same test again.

If the sled took any coolant after bleeding that’s a sure sign there was an airlock. The other way to alleviate this issue is to lift the front of the sled higher than the tail where the coolant crosses over and returns via the opposite side cooler to the engine.

The air lock is almost always right at the rear of the coolers – or the highest point in the system. That’s why the pump can’t get the coolant to return. If you elevate the sled’s nose, loosen the coolant cap and open the bleed screw the air lock will usually move out quickly and the coolant level will go way down – of course this is the indication there was an air lock and you must now top it off.

Another trick is to start the sled up when the nose is elevated and the coolant cap is off. This will speed up the process as well. If this isn’t what’s going on then you need to check to see if your cooling system has a blockage.

You can verify all of this by simply idling the sled and feeling the coolers warm up as I suggested earlier. If the coolers are not evenly warm, you have a circulation problem.

Hope this helps,

Motorhead Mark

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