M8 Liquid Cooled?
Seasoned HDF Member
Joined: May 2012
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From: Carlsbad, CA
The cooling either by oil or water based coolant is for rider comfort. It is designed to take heat out of the hottest part of the head that is the known cause of roasted chestnuts. It does nothing to cool the motor. In fact, if you have a cooling motor failure it is perfectly safe to ride as it is.
HDF Community Team
Joined: Sep 2013
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From: Wisconsin
The cooling either by oil or water based coolant is for rider comfort. It is designed to take heat out of the hottest part of the head that is the known cause of roasted chestnuts. It does nothing to cool the motor. In fact, if you have a cooling motor failure it is perfectly safe to ride as it is.
Another thing to note about the M8 Twin-Cooled Touring Models that have radiators and a water pump....They have no oil cooler, resulting in the oil having a very difficult time shedding heat. The M8 Softails have a large oil cooler, with no where near the heat build up in the oil as the Twin Cooled Touring Models.
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Last edited by DK Custom; Nov 4, 2019 at 01:47 PM.
HDF Community Team
Joined: Sep 2013
Posts: 2,352
Likes: 2,311
From: Wisconsin
Another thing to note about the M8 Twin-Cooled Touring Models that have radiators and a water pump....They have no oil cooler, resulting in the oil having a very difficult time shedding heat. The M8 Softails have a large oil cooler, with no where near the heat build up in the oil as the Twin Cooled Touring Models.
In our testing, at speed, or in stop n go, the twin cooled bikes have a very high oil temp build up that is a result of there being very little provision for that oil to shed any heat.
HDF Community Team
Joined: Sep 2013
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From: Wisconsin
Thanks for the info, I would not have thought that to be the case.
Road Warrior
Joined: Nov 2018
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From: SW Ohio
As you noted, the liquid cooling only goes between the exhaust valves. Does not do much (or anything) to cool the oil that gets heated up by squirting on the bottoms of the pistons. On the Softails, even in stop n go traffic, at least there is a way for the oil to shed a little heat as it flows thru the monster oil cooler.
In our testing, at speed, or in stop n go, the twin cooled bikes have a very high oil temp build up that is a result of there being very little provision for that oil to shed any heat.
In our testing, at speed, or in stop n go, the twin cooled bikes have a very high oil temp build up that is a result of there being very little provision for that oil to shed any heat.
HDF Community Team
Joined: Sep 2013
Posts: 2,352
Likes: 2,311
From: Wisconsin
The softail uses a different oil pump and the oil cooling loop, so, yes that is a possibility.
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Seasoned HDF Member
Joined: May 2012
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From: Carlsbad, CA
oh, youre right. Thats why they started the wet head cooling with the Rushmores. But wait...the Rushmores were only 2 valves per cylinder...Never mind.
Road Warrior
Joined: Nov 2018
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From: SW Ohio
Most likely you both are correct. The liquid cooled heads on the touring bikes were for rider comfort and to help the engine maintain higher output. The additional cooling around the exhaust valves was needed for the 4-valve configuration.
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