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What is an Oil Cooler?

By Mike Howells
Updated May 23, 2024
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An oil cooler is essentially any device or machine intended to cool oil, but in most instances people talk about it in the context of cars, trucks, and sometimes airplanes. In these settings the cooler basically acts as a small radiator that helps keep an engine cool by keeping the oil supply at a consistent temperature. Cooled oil helps keep the engine running smoothly, particularly during gear changes in very hot weather or on long-haul trips when things might otherwise have a tendency to overheat and break down. Not all cars and trucks use oil as a coolant, but those that do really depend on a working cooler in order to get good efficiency and performance.

Main Purpose

Automotive engines tend to be somewhat complex, and usually depend on a series of different combustions, heat sources, and temperature regulators in order to function properly. Oil coolers are most common in heavy-duty machinery that has a more industrial-grade engine. Trucks used to haul freight and large vehicles designed for off-roading are two common examples; some recreational vehicles (RVs) and airplanes have them, too, and they may even be found in certain motorcycle models. Race car drivers sometimes add them to sports cars to make them more efficient, too, and to improve their fuel combustion times.

A transmission oil cooler is often considered essential in high-strain situations because a transmission's lubricating fluid heats up with each gear change. While not crucial for highway driving when vehicles more or less stay within a few gears, 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.

Even though the main job is to cool and lubricate the engine, this part can also act as an important coolant for a number of other parts. A motor's bottom end, which includes parts such as the crankshaft, bearings, camshaft, rods, and pistons, is also cooled only by engine oil, for instance, and this cooling can impact overall performance just as much as it could in the engine itself.

Types

Engine oil cooler design can generally be split into two types. Tube and fin models are the first, and are designed so that oil circulates through cooler lines that surround the engine. As the oil moves away from the heat of the central engine, its temperature drops and excess heat is funneled out by fin-like vents attached to the tops or sides. Stacked-plate designs, by contrast, force oil through a series of metal plates. Heat dissipates as air moves across the plates, and the oil cools faster when it has greater surface area and is shallower, too.

Plated models are often slightly less effective at cooling oil than their tube and fin counterparts since they’re more passive, basically waiting for cooling to happen on its own. A lot of this depends on the application, though. In some settings, stacked plate coolers make more sense.

How They Work

In a stock setup, transmission fluid is cooled as its collected heat transfers to the colder engine coolant that surrounds it. Coolers usually work best when mounted in front of a stock radiator since this is where it can often get the most unobstructed source of cool air. This, in turn, allows much cooler fluid to return back to the transmission case.

While a majority of cars are not manufactured with proprietary engine oil coolers, there is a large aftermarket for them in many places, and they are common accessories in vehicles involved in towing and other heavy-duty applications. People can buy oil cooling kits to upgrade their vehicles themselves, though this usually requires a bit of expertise. Many professional shops will also install these for people looking for ways to make their machines more efficient.

Common Problems

The optimum temperature for oil is usually 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, which can begin to degrade the oil. Oil loses its lubricating, as well as its cooling, properties when it starts to break down, and this can lead to a number of serious engine and transmission problems. Coolers should usually be inspected fairly regularly to keep them in good working order, and owners should take care to regularly inspect and service them to avoid major failures.

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Discussion Comments
By anon113008 — On Sep 22, 2010

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

By anon110911 — On Sep 13, 2010

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

By anon96719 — On Jul 16, 2010

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

By ValleyFiah — On Jun 18, 2010

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.

By Babalaas — On Jun 18, 2010

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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