Latest Industry News

Ouch! That’s Hot! Adding Transmission and Engine Oil Coolers

Two mechanics adding oil level in a car workshop

Many vehicles come with a standard radiator and no engine or transmission cooler. This is usually fine unless you do a lot of towing or haul heavy loads. The engine oil and transmission fluid have two jobs – the main job is to lubricate moving parts. However, engine oil helps cool the engine and transmission fluid helps cool the transmission. As the fluids move through their respective parts, they pick up heat generated from the engine and transmission. Even if the fluid lines pass in front of or through the radiator, it’s not enough to dissipate the amount of heat these fluids pick up.


Transmission Oil Cooler Assembly

What Are Engine and Transmission Coolers?

Engine and transmission coolers look like small radiators. The fluids enter one side and leave the other as they are circulated through the engine or transmission. Thin pipes are attached to fins to very effectively dissipate the heat the engine oil and transmission oil absorb.

According to Lynden Abel, in a Motorweek interview, many people believe oil coolers only work at higher speeds. However, they are also effective in stop-and-go traffic and when you are not moving. You can test this theory by putting your hand near the engine oil cooler or transmission fluid cooler while the vehicle is running and parked. You can feel a lot of heat coming off the coolers.


But… What About Winter Months?

If you purchase an engine oil cooler or transmission fluid cooler with its own thermostat, it keeps the oil cooler from overcooling the oil. The thermostat also allows the oil to come up to temperature quickly, so it boils off the moisture that gets into the engine oil and transmission fluid. Once the oil reaches 212 degrees Fahrenheit, which is the boiling point of water, the heat causes the water to dissipate.


Oil Integrity and a Longer Life

Without an engine oil cooler or transmission fluid cooler with thermostats, the oil or fluid could stay cooler than 212 degrees and never boil off the condensation that builds up. When this happens, the fluid degrades much quicker. If the oil or transmission fluid rises above 260 degrees Fahrenheit, the engine oil and transmission fluid are not as effective.

When engine oil gets that hot, it thins out, causing lower oil pressure, especially while you are idling or when the engine is at lower revolutions per minute, such as when you are driving 25 to 30 miles per hour. When the pressure is lower, the engine oil pump and the front pump in the transmission turn slower.

The integrity of the oil degrades faster, which means that before you get to the factory recommended interval for an oil change, the oil could already be too thin and not provide the proper lubrication for the engine.

The internal workings of the engine and transmission – but especially the engine – have tight tolerances – down to a few thousandths of an inch. If not properly lubricated, the heat causes parts, such as piston rings and bearings, to wear out faster.


Stock vs. Towing vs. Racing

As with racing a vehicle, towing makes the engine and transmission work harder, which means that they produce a lot more heat. The oil temperature in a stock vehicle might reach 220 degrees Fahrenheit. However, when racing or towing, especially if you are towing heavy loads, the engine oil and transmission fluid could reach temperatures as high as 300 degrees Fahrenheit – more so when it’s a hot day.

Installing a quality engine oil cooler and transmission fluid cooler can extend the life of your vehicle and significantly mitigate engine overheating when towing, especially when you are towing uphill on a hot day.


Contact Mac’s Radiator Today for Quality Engine Oil Coolers and Transmission Coolers

Extend the life of your vehicle’s engine and transmission, and help the engine run cooler – which helps with fuel economy, too – by calling one of our Oregon and Idaho locations for engine oil cooler and transmission cooler installation and to learn more about the other services we provide.



Mac's Radiator is the best mechanic to help you with all of your mechanic needs!  Let Macs help you - we are located in 6 convenient locations, for when you need us close to home, or when you're on the road.




Portland, OR      (503) 777-4706
Beaverton, OR  (503) 646-2943
Bend, OR            (541) 382-6963
Boise, ID            (208) 344-1722
Eugene, OR        (541) 344-0253
Salem, OR          (503) 364-7129

Back to top