2010 Sportsman 550 EPS overheating & resol - Polaris ATV Forum
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post #1 of 2 (permalink) Old 05-03-2019, 12:31 PM Thread Starter
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Join Date: May 2019
Location: Pacific North West
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2010 Sportsman 550 EPS overheating & resol

First post, please be kind, Iím not a mechanic.

A few days ago I took my grandkids for a short ride on the quad and had to cut it short due to overheating. First thing that I noticed was the radiator was steaming, the fan wasnít running and the CEL ( check engine light ) was on.

After researching the forums I tried disconnecting the engine temp sensor and the fan came right on. Check, fans ok, relay is ok, fuse is ok. After another test ride with the fan running I checked the radiator input and output temperatures with an IR ( Infra Red ) thermometer. Measuring about a 30F difference between the radiators input and output, I guessed that the water pump was working and the thermostat was probably ok with that much of a temperature difference.

After picking up a new engine temperature sensor I measured the resistance of both new sensor and the original, presumably failed sensor. New sensor 30K ohms at 70F, failed sensor 60K ohms at 70F. Just for fun I recorded some resistance readings at various temps. New sensor 10K ohms at 130F, 7K at 150F, 5K at 160F, and 3.5K at 180F. Like I said, Iím not a mechanic, just love to fix things.

Most importantly the CEL extinguished immediately after plugging in the new engine temp sensor. Thank goodness the trip to the dealer was avoided to reset the CEL. Some forum post suggested there may be a second temp sensor on either the side, or bottom of the radiator. I never found one.

Relays: If you isolate your issue to a relay I found the Song Chuan OEM relay ( # 303-1AH-S-R ) sold by Mouser.com for about $3.25 each + S&H. If you want to check the coil it should measure about 125 ohms plus or minus 10%. The contacts are normally open and can be operated with a 9V battery for testing.

In conclusion, I went for about a 20 minute ride to check out the repair and the fan came on as it should, and the engine stayed cool, so Iím happy. Comments & insights appreciated, I hope the info helps someone.
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post #2 of 2 (permalink) Old 05-04-2019, 06:32 AM
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Join Date: Nov 2009
Location: SE Kentucky
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Sounds like you're doing a pretty good mechanic imitation to me!
You identified the problem. Isolated the faulty part and tested to confirm. Replaced the bad part and tested to confirm the fix. Don't know what else a real "mechanic" could have done any differently other than make your wallet substantially lighter during the process.
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