Keeping Your Motorcycle Cool with Oil Coolers

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July 26, 2010 | By: Scott Holton

One thing many of us do in preparation for hot weather is buy an oil cooler. It makes perfect sense, because the oil in an air-cooled engine performs a major role in cooling the engine. Does this mean an oil cooler will enable the oil to do a better job? Well, yeah, sort of — to a point. Fact is, oil coolers do a great job of cooling the oil, unless you pick the wrong unit for your application, or the unit’s not properly installed. In either of those cases, an oil cooler can do more harm than good.

Oil has a tough role in Harley engines. It has to be able to flow through very small holes, into very small passageways at very low temperatures. And it must be able to resist thermal breakdown at high temperatures. Plus, it’s got to remain slippery enough to lubricate high stress points, such as piston rings and skirts, valve stems and tappet bodies, but not so slippery that it promotes hydroplaning or roller sliding.

When the engine gets hot, oil begins to deteriorate. As thermal breakdown occurs, the additive package (the chemicals in the oil that give it particular properties or characteristics) begins to break down. A good high-quality oil cooling system can go a long way in preventing this process from happening.

The first thing you need to consider when purchasing an oil cooling system (notice I said system) is the design, along with mounting hardware. A good oil cooler should be well constructed, with heavy fins in a solid frame and a heavy mounting bracket. The unit should be small enough to mount unobtrusively (Harleys look funny with radiators) yet still contain adequate surface area to promote efficient thermal transfer. Surface area is the key factor here. The more surface area you have, the greater its heat transfers properties. In the past, some oil coolers were designed with cooling fins on the inside of the passageways. Sounds good on paper, but there are some inherent problems with this feature, especially when it comes to Harley-Davidson engines. Since the oil cooler must be installed on the return side of the oil pump, the scavenge system is often overtaxed in its effort to overcome the additional resistance to flow created by the oil cooler. When that resistance is compounded by internal fins in the oil cooler, the result is usually oil carryover from the crankcase vent.

Whatever type of oil cooler you choose, make sure it’s installed in conjunction with a thermostat designed to open at no less than 180 degrees. This is where the “system” in oil cooling system comes in to play. By not having a thermostat, oil is prevented from reaching normal operating temperatures and thus fails to scavenge contaminants from the engine. If the engine is using heavy-grade straight-weight oil, there may be additional damage from oil starvation at critical lubrication points. And if it looks like you can’t install a thermostat, there are optional bypass valves available.

Comments: 9 Comments | Categorized Under: Tech Tips

Comments (9)

best deal i’ve seen is the Jagg 10 row set up. less pressure drop across the unit than with an 8 row harley unit. a big plus is the Jagg has turbulators which spin the oil to keep it stirred up while circulating and not just push through. that tends to cause adiabatic cooling of the stream and does not work efficently. go with Jagg.

A oil cooler is a great purchase reguardless of the price. for two reasons. 1. it adds to the oil capicity of the engine. 2. it allows the oil reguardless of city or highway driving,to circulate out of the hot motor to be exposed to cooler temptures. So if your someone is that concerned about the engine oil temp. have one enstalled. so unless you go cheap, you can’t go wrong.

What do you think of the Ultra Cool oil cooler

Hmmm, I was just thinking about an oil cooler for my Revtech Chopper and what Mr. Clark said really struck a nerve. I almost never get a chance to drive above 45 mph on my bike and if I do, it’s a matter of minutes. An oil cooler would have little effect. Thanks for saving me a bit of cash bro!

I’ve recently started a blog, the information you provide on this site has helped me tremendously. Thank you for all of your time & work.

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Where is Harley Davidson on this?
My legs burn up at the stop lights. I thought of a parade fan too. Why aren’t cooling tubes built into the oil pan?

This is all good information and well thought out. However, in my experience with Harley Davidson owners, the issue was a matter of common sense rather than keeping the oil at a good operating temp. As a parts sales person in Arizona I had many customers come in to buy an oil cooler. The one thing that you hear the most about Arizona (especially in Phoenix it seems) is that it’s a “dry heat”. So, the first thing I would ask the customer is “do you drive in a lot of city traffic”. Meaning that most of the riding is on surface streets and light to light as a commuter. If that was the case an oil cooler was going to be less efficient due to the lack of air flow through the cooling unit. Granted it would help some but not enough to warrant paying the price of some oil coolers and the service department cost for labor. My suggestion was to install a Parade Fan which would help keep a continuous flow of air over the engine. The end effect was heat transfer away from the motor. The oil cooler would work if the bike was being ridden on the highway but for surface streets it would have been a visual reminder of money blown.

My point in all of this is that anyone thinking of adding an oil cooler should first ask themselves 1) what type of riding do I do the most? Commuting on surface streets in traffic or more touring away from congested roads. 2) is the climate that I primarily live in going to help the oil cooler do what it is designed to do?

Again, just my thoughts and experience.

anytime you can drop the temp in oil,even synthetics, is a good thing. the problem I see on any bike, is areas to mount coolers that will efficiently cool the oil in any driving circumstance.

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