thermostat
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Seasoned HDF Member
Joined: Oct 2012
Posts: 11,198
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From: St.Louis Mo.
thermostat
what would happen if you just left the thermostat out of the bike ? run cooler ? i know it would take longer to warm up, but i wouldn't think anylonger than an air cooled one.
Stellar HDF Member
Joined: Sep 2013
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From: USA
The way it is written, it sounds like the thermostat diverts the coolant to the radiators above 165*. I don't know it the hot coolant would flow thru the radiators without the thermostat. The hot coolant might just follow the path that the coolant takes before opening the thermostat.
I wonder if that was what happened here because the thermostat was defective:
https://www.hdforums.com/forum/new-r...ot-update.html
Stellar HDF Member
Joined: Sep 2013
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From: USA
AS Wharf Rat said sometimes the coolant flows to fast to be cooled without the restriction created by the thermostat. I've seen that occur in cars.
Last edited by 14GuineaPig; Apr 11, 2016 at 05:09 PM.
Road Master
Joined: Mar 2015
Posts: 904
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From: Denver Colorado
It won't run any cooler, just like a car, the thermostat opens at a minimum temperature, has nothing to do with controlling max temperature. Once it opens it stays open until the temp falls below that minimum temp. People think that if they put a lower temp thermostat it will lower the engine temp, doesn't work like that.
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Seasoned HDF Member
Joined: Oct 2012
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From: St.Louis Mo.
i know it would slow the heating up of the engine with no effect on max temp. wonder if the ecm would cause problems ?
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Road Master
Joined: Aug 2009
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From: new york
Without the thermostat the coolant could flow through the system to quickly, the coolant needs time to pick the heat up the heat in the heads and transfer to the radiators. The temp/degree of the thermostat is only for the minimum temp opening.
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Thread Starter
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Seasoned HDF Member
Joined: Oct 2012
Posts: 11,198
Likes: 3,028
From: St.Louis Mo.
after reserching this it seems the ecm will read the differance between the engine temp and engine coolant temp. to big a differance and it will throw a check engine light with a code.
Stage I
Joined: Apr 2025
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Bypassed thermostat and replaced pump
Because Harley decided to make the 103 coolant system obsolete. I have bypassed the thermostat and replaced the pump with a secondary pump from a 2006 to 2009 Audi A3 Quattro that's available on Amazon. So far so good. I'm going to put some miles on it and give an update soon if it works and include a couple pics of the setup.