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Water Pump or Thermostat?

Posted: Wed Jul 08, 2020 9:25 pm
by Wilcoy02
Was looking to change the anti freeze on my GL1100. Had the engine running for 15 mins or so. The fan came on and temp gauge half way up.

I had the radiator cap off and watched the water in the neck of radiator. It never circulated.
Do I have a thermostat problem or do I have a water pump problem? How do I check ?

I really do not want to tear into the radiator.

Re: Water Pump or Thermostat?

Posted: Thu Jul 09, 2020 6:51 am
by DenverWinger
You won't see it circulating there. If the bike hasn't been overheating (i.e. Temp gauge full scale and Steam/coolant from the overflow) I'd just put the new coolant in and ride it like you own it! :)

Re: Water Pump or Thermostat?

Posted: Sat Jul 11, 2020 10:36 am
by bofler
Thermostats fail, but you're probably ok if your fan is coming on. My fan comes on with the needle at about 2/3 across the temp gauge. Was that way with my old thermostat and is that way with the new one I put in when I swapped timing belts and radiator hoses recently. The only way to check this in an accurate way, that I can think of, would be to measure engine temp when your fan kicks on and/or get the thermostat out and put it in hot water and see at what temperature it opens.

Assuming you're not having problems with overheating, then your water pump (and thermostat) should be alright. When pumps fail there will likely be some fluid dripping from the weep hole on the left-front side underneath the bike.

No drips, no oil in the reservoir, and fan turns on when you're moving slowly or sitting. Should be fine to ride.