No expert on fans.. but my guess is all radiators get their main cooling ability from fresh moving cooler than the motor air.. the assist of a fan is likely just a little extra help when there is no air movement like sitting in traffic.

‘’Mounted behind I would think you’d severely limit its ability to cool with the limited air movement. Not to mention the hotter air from both cylinders and exhaust. Last I would guess there to be a lot of debris and possibly some high speed rocks thrown at it from the tire. But who knows.

 

1. Most radiator systems primarily rely on fans moving air through them. Coming from cooling PC CPUs and GPUs, liquid cooling systems use radiators just like the ones on the front of the bike, and these ultra cool systems. There are even fans that are optimized for high static pressure specifically to push air through radiators and not allow it to run back through the fan.
2. Spinning tires "Paddlewheel" air currents around them. If you've ever gotten close to a spinning disk or tire or touched a spinning tire you'll feel there's air coming off of it. As the rear tire spins it pulls air around it, especially at higher speeds. This creates a flow of air that clings around the tire and will pull fresh air under the fender. This air flow will be pushed further around by the fans of the cooler being oriented in plane to the ground, with the fans ontop of the rad under blowing towards the ground.
Meaning the fans will draw air from the underside where the tire has drawn in cooler air. The exhaust of the radiator will spill onto the ground/under the frame.

Alternatively you can simply just flip the fans over, and draw air directly from the airstream below the motorcycle, but this will inherently have to fight what air is being paddlewheeld into the area behind the bike that's moving in an opposite direction.

The Ultracooler uses 220CFM fans which are pretty much equivilent to industrial PC fans. Which if the radiator is a 140mm x 2 fan configuration, I could replace the stock fans with Noctua NF-A14 300 industrial fans which blow 270CFM @ 3000RPM.

3. The back of the bike frame has a mud/splash guard, and there is a battery box and electronics sitting between the engine and where the radiator would be suspended. The rad would be close to the transmission case, but it's no closer or wouldn't be any warmer than the radiator upfront.
Besides, any air that the fans draw in regardless of their orientation will be dramatically cooler than the radiator itself.

 

I`m in SC, and not considering an oil cooler on any of my bikes, 3 of them came with oil coolers, good enough for me.

People are obsessed with the idea that the engine is going to self-destruct because of heat.

It`s a motorcycle, they get hot.

Ride the thing and stop worrying.

 

Its another solution looking for a problem. A big waste of money and a hideous eyesore to the beautiful lines of a softail.

As long as I can remember, people who ride Harleys obsess over oil choice and heat…among other things. The engine has been developed and tested in the desert. Harley’s engineering test track is in the desert. Too many folks are looking at temperature gauges and pretending to be engineers…but hey its your money so do whatever lets you sleep at night.

Bottom line is the M8 top end is good for 100K miles without your redneck engineering solutions. The bottom end is good for two top ends. The engine can handle more heat than you can as a rider.

 

A lot of these comments come from people who like their bike stock. So the engineered solution is great because their bike is stock. But my guess is 1/2..maybe 3/4 of us don’t run stock.

It doesn’t take a wizard to realize if stock made 56 hp with the factory designed cooling and you’re now making 150hp that the stock solution is no longer sufficient for the far greater operating temperatures your experiencing.


So while some are very dogmatic in their opinion that increasing your cooling is foolish or un-needed I think they assume everyone wants the stock anemic power.

Let’s not be foolish and believe when you up power you don’t have to up everything else to support that power.

Lets face it increasing compression raises heat. Increasing stroke raises heat.
Increasing Bore raises heat.
Most performance cams raise heat.Raised rpm power band raises heat…

 

That sounds like a well researched thought out answer. Who knows maybe you’re right. But I’d worry it’s a great theory and not as great put into practice.. but that’s just me. The air off your tire is Hot air due to friction and road radiant heat. So hot in fact your tire circumference enlarges forcing the tough rubber to expand. There are grooves purposely engineered to discharge heat by being absorbed by the air around it. Your exhaust radiant heat not just tail pipe air is super hot and also trying to dissipate heat past the back cylinder. The fans at 200cfm… heck 500cfm are probably still not as much air as a cooler infront in the wind at 80mph. So again, maybe you’re right. But it defies my practical thinking although possibly flawed.

 

agree that raising compression raises heat and all things being equal, a high performance build can generate more heat. Having said that, at least from my Twin Cam experience, I have seen good tunes seem to cool the engine down. I have had several built Twin Cams but nothing super radical. My current CVO 110 was properly built to a 117 Stage IV with a full decat and SE Race Tuner (non EPA) and it is much more comfortable to ride than stock. I kept compression to 9.9:1 while stock was 9.3:1. The 117 feels cooler than the 110 ever did. I don’t have measurements to say it is a fact but it does feel more comfortable. That 110 was the hottest engine I have ever owned…or at least it felt the hottest when riding it.

I suspect that if most folks do a M8 build and don’t go radical but simply do a nice midrange cam, big bore, etc., they might see a more comfortable ride in terms of heat. This assumes they get a non EPA exhaust and tuner and get a proper tune. Even Harley’s full EPA compliant and warranty compliant big bore kits do not require any supplemental cooling. I believe that is the case for kits all the way to 131 Stage IV.

All of my comments are based on applying some common sense. I occasionally get caught in the proverbial traffic stop or something but I do not sit in stopped traffic and let my bike run for long periods of time. Just a few weeks ago, I was caught in stopped traffic for about 1/2 an hour and I shut my 2023 Breakout off after about 5 minutes and waited. No need to sit there for 30 minutes and let it run while I sit on top and cook. I avoid big cities like the plague too but yes, I do occasionally ride through a city in 90 degree heat. Not pleasant….

 

In my world even getting to the back roads can mean you get 5 miles in 30-45 minutes most week days. You can’t shut it off. Many traffic lights can be 7-8 minutes. And you might have to wait on the second one.

A tune is not some magic thing that creates greatness. You either have it poorly tuned and then it’s tuned correctly.. the tune didn’t make it run cooler. The tune made it change from wrong to right. If you add fuel to cool the motor accross the bands… a tune can be used to do that the same as a carb. But when it’s tuned correctly, possibly a tad rich to help with cooling a performance motor can still run very hot. 1/4 of my riding season is above 95 degrees out. With heavy traffic.

 

Not saying that a tune is magic…what I am saying is that they are inherently lean (EPA compliant) when stock and when tuned properly (read non EPA compliant), they run cooler. I have had several built Harley’s and all ran better than stock. And by better, they had more power and seemed to run cooler than stock because of a non EPA tune. A little richer A/F ratio is good for an air cooled motor and yes, we were all running our carbs a little rich too back in the day.

Also, when ridden normal, I saw no loss in fuel economy on any of my built motors including my current 117 Stage 4 Twin Cam.

My 2023 Breakout 117 will get built too and properly tuned (non EPA tune). I will get a Power Vision and have it properly dyno tuned for the build. No, it won’t be magic, but it will run properly and my guess is it will be more comfortable to ride even though it is built. I am not building race motors. I am building reliable street motors that get rid of EPA choked down components…like the stock cams, exhaust, tune, etc.

I still say these add on oil coolers are a solution looking for a problem but to each their own. If it removes anxiety and worry, then by all means add it. I just don’t believe many of these bikes need it or are built to a point that they need it. As I stated above, even the 131 Stage 4 kit doesn’t require any additional cooler to be added and Harley will warranty that engine for up to what…7 years with unlimited miles?

 

I finally got my Ultracool installed and road tested with no oil leaks, just needed really tighten the oil line connections after test ride. I also added a bug screen to try and keep the cooling fins semi free from road debris with no impact on air flow to the cooler.

Prior to the Ultracool install, my oil temps would read 230 to 250F and after the install, my oil temperature dip stick never when over 205F to 210F for the first time while riding in the 90s+ here in the Southwest during this time of the year.

This 117 M8 runs hotter vs my 114 RGS.