Do Fan Cooled Motors Lose Power After Warm-Up?

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I have a 550 Fan cooled Polaris; I read in another magazine that fan cooled motors lose some of their power after they warm up.

I know liquid motors run cooler and make more power. Is this a big problem for the fan cooled motors? Should I be concerned about it? What can I do to help the motor?

Thank you for your time.

Mike Rohwedder


Fan cooled engines do not lose power when they get up to operating temperature – they’re designed to make their claimed HP at temperatures experienced under normal operating conditions.

Any 2 or 4 stroke engine, liquid or fan cooled will suffer from decreased power when temperatures go outside of the engine’s design limits. Example: If you operate a liquid cooled sled and do not have adequate snow on the coolers in the tunnel it will ultimately overheat, loose power and seize.

If you operate a fan cooled with the hood vents blocked or under huge loads on a 50 degree F day, it will over-heat, loose power and seize.

In actual fact, fan cooled engines are less likely to have severe overheating problems as they do not rely on snow to cool them.

Fan coolers use air (always present – albeit it can become too warm) and fuel – (always present and always relatively cool). Fuel is a very important and reliable part of the cooling system for a fan cooled engine.

This is why a fan cooled engine is generally not as efficient as a liquid cooled motor – the fuel is performing two jobs – cooling and energy for combustion.

The reason you have heard this story relates to this reality. When you increase specific output in a given displacement engine it will produce more heat. Example – a fan cooled 550cc mill will deliver about 60 ponies.

If you port and time the same 550cc displacement mill to produce 100 HP – easily attainable – the engine must be liquid cooled to live. Get it?

Your 60 HP motor cannot be hurt or improved with extra cooling – provided you are operating it within its design parameters.

Enjoy it and don’t worry about cooling.

Motorhead Mark

Supertrax Online
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