What Is an Oil Cooler?

A stacked-plate style oil cooler.
An oil cooler keeps the oil in an engine at a constant temperature.
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  • Written By: Mike Howells
  • Edited By: Michelle Arevalo
  • Images By: Moto "club4Ag" Miwa, Georgi Roshkov
  • Last Modified Date: 19 April 2014
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An oil cooler is a separate, smaller radiator from an engine's main radiator, which maintains an oil supply at a consistent, optimal temperature. Broadly put, lower oil temperatures prolong the life of an engine or transmission. A cooler can play an important role in the smooth running of a vehicle by dissipating heat while transporting oil away from moving parts into the oil pan.

The optimum temperature for oil is between 180° and 200°F (82° and 93°C). Failures start to occur when oil cannot dissipate its collected heat fast enough and rises past this threshold. As it begins to break down, oil loses its lubricating, as well as its cooling, properties.

While a majority of cars are not manufactured with proprietary engine oil coolers, there is a large aftermarket for them, and they are common accessories in vehicles involved in towing and other heavy-duty applications. There are oil cooling kits for both motors and automatic transmissions. In engines, oil not only functions as a lubricant but also as the coolant for a number of parts. A motor's bottom end, which includes parts such as the crankshaft, bearings, camshaft, rods, and pistons, is cooled only by engine oil.


Engine oil cooler design can be split into two types: tube and fin style, and stacked-plate design. Tube and fin style coolers are designed so that oil circulates through cooler lines — the tubes. As the oil circulates, the lines dissipate the heat through the fins. The stacked-plate design forces oil through a series of plates, with heat extracted as air moves across the plates. This more passive design is significantly less effective at cooling oil than tube and fin.

A transmission oil cooler can be essential for automatic transmissions used in high-strain applications, because a transmission's lubricating fluid heats up with each gear change. While not crucial for highway driving in which gear changes are minimized, transmission coolers can markedly improve the performance and longevity of transmissions that are subjected to a great deal of stress. Overheated transmission oil can lead to slower gear shifts, worn seals, lower mileage, and, ultimately, premature failure.

In a stock setup, transmission fluid is cooled as its collected heat transfers to the colder engine coolant that surrounds it. For maximum effectiveness, a cooler works best when mounted in front of a stock radiator, as it is there subject to an unobstructed source of cool air. This, in turn, allows much cooler fluid to return back to the transmission case.


Discuss this Article

Post 6

how can you tell if it's the head gasket or oil cooler on a tx4 taxi oil in reservoir?

Post 5

The only issue I have with your article is the comment that the stacked plate design is less efficient that the tube design like Perma Cool. B&M is an example of a stacked plate design. The point is that the stacked plate design is about 20 percent more efficient than the other tube design. Over the years the RV magazines will have articles on this subject.

20 percent better for the given surface area is about standard. What makes the stacked plate design better is the clever way that they twist the oil as it goes through the plates. Without the twisting, the oil congeals around the edge of the cooling tubes and insulates the fast moving oil in the center of the tubes. 20 percent efficiency is lost.

Believe it or not, I run B&M oil coolers in an experimental Lycoming aircraft engine that I own. Even the fancy expensive aircraft oil coolers don't cool as well. I know, I know, I sound like a B&M shill. Cheers

Post 4

thank you. it helps to understand the Oil filter and oil cooler. thank you.

Post 3

My buddy has a turbocharger on his truck and he replaced the stock tube and fin oil cooler system with a custom water cooled set-up. Basically there was a spacer placed between the block and the oil filter that ran coolant around the oil filter mount. This system keeps the oil at a fairly constant 185 degrees; which is a little cooler than the stock system. This kept the oil pressure a little lower under hard use. Because of the increased load on the coolant system, he did need to upgrade the radiator fan so that it could keep the coolant temperatures in a reasonable range.

Post 2

I have an oil cooler on my truck and I learned the hard way that they can be sensitive to rocks. I took my truck out on the trail and a rock ran up underneath the front end. The oil cooler on my truck sits a little lower than the radiator; close to the bottom of the bumper. The rock kinked one of the return lines and created a leak.

Luckily I wasn't that far in on the trail, so I was able to call a buddy to come and tow me out. When I got back I had to buy a new oil cooler kit which cost about $150; about the same price as a skid plate. Which; by the way, is the same after market part that is meant to protect all of the sensitive equipment under the bottom of the front end.

It was a boneheaded move that set me back $150 and a few hours of my time. Once it was repaired one of the first things I did was buy a skid plate.

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