Guide To Engine & Transmission Oil Coolers

Updated Jan 31, 2019

Upgrading engine and transmission cooling systems is cheap insurance for preventing overheating issues

Gas or diesel, two-wheel-drive or four, today’s pickups and SUVs are remarkable vehicles. They are much more comfortable than those of yesteryear, their engines are making a lot more power with better fuel economy, and the transmissions are velvet smooth.

Cooling systems are also improving with each new model, as well. In fact, today’s new pickups are far more advanced than those found back five years.

That’s because every year the vehicle manufacturers drivetrain engineering teams take their new models to the desert Southwest in mid-summer, load them to the maximum trailer and gross combined ratings, then drive them up the steepest grades in triple-digit heat time and time again.

Such extreme testing is done to make sure the factory cooling systems are capable of sustaining operating temperatures within the safe working zones for both engine oils and transmission fluids.


But if your fleet is using older pickups, or buying used ones that are 5- 10-years old and refurbishing them for heavy-duty towing use, you need to take a close look at the cooling systems.

Daily towing in high-humiidity, and or towing in temps that are above 90-degrees put a lot of strain on older truck’s ability to keep transmission and engine temps in check-esepcially diesels.

Auxiliary coolers, which typically cost between $100-$200 for a good quality unit, can ensure a long, healthy life of the trans and engine.


New trucks, such as this 2015 Ford F-450, have state-of-the-art cooling systems. Older trucks may not have that cooling capability.New trucks, such as this 2015 Ford F-450, have state-of-the-art cooling systems. Older trucks may not have that cooling capability. 

Every engine makes heat. The more fuel you pour to the engine, and the heavier the load it’s trying to pull, the more heat is generated. Here’s a short course in why that happens.

Gasoline produces about 125,000 BTUs per gallon—that is the equivalent of burning nearly 16 pounds of wood inside the engine block for every 10-12 miles you tow a trailer or slog through the mud.

Diesel has even more thermal energy, producing 139,200 BTU per gallon. By comparison a gallon of propane only makes 91,500 BTU, while a pound of wood makes around 7,900.

Imagine how hot it is sitting around a roaring campfire.

Now imagine sitting around the same campfire burning gasoline or diesel instead of wood. If your truck is getting 10 miles-per-gallon towing a big trailer, that’s almost the same as pouring in a pint of fuel into the block every 60 seconds to stoke the horses.

Fortunately, about two-thirds of an engine’s heat is transferred into mechanical power or goes out the exhaust pipe. The other third remains as pure heat that has to be removed by the engine’s two fluid cooling systems—water and oil.


Manufacturer’s online towing guides specify weight limits and towing equipment for all their models.Manufacturer’s online towing guides specify weight limits and towing equipment for all their models.

The water/coolant mixture that flows through the radiator, transfers heat from the cylinders, engine block, heads, and intake manifold to the cooler air flowing past the radiator tubes from the outside.

Engine oil does its part, too, as it’s constantly pumped over and around bearings, lifters, gears, chains, camshaft, crankshaft, connecting rods and pistons. On high-performance engines and most turbo-diesels, small “jets” spray oil at the bottoms of the pistons to remove heat from these heavily-stressed areas.

In some cases engine oil runs through a “water-to-oil” cooler in or attached to the block. The advantage is that the oil is warmed up by the coolant to reach ideal operating temperature sooner; the disadvantage is that after initial warm-up the oil will never be cooler than the coolant and may overheat sooner.

An automatic transmission also generates heat from friction between gears and clutch packs and shear loads in the torque converter. The heavier the load, the more friction and heat is generated.

Transmission fluid (oil) handles that cooling task as it circulates to the transmission cooler, which in most instances sits in front of the radiator. That cooler positioning is because transmission fluid temperatures are the most critical of all the fluids. But we’ll get to that in a minute.

Although much smaller, many modern vehicles come with a small power steering fluid cooler, often just one or two tubes across the front of the radiator.

Installing a Flex-A-Lite dual fan/high-flow radiator combo on older diesel pickups greatly improves cooling effciency.Installing a Flex-A-Lite dual fan/high-flow radiator combo on older diesel pickups greatly improves cooling effciency.

Power steering uses fluid similar to ATF and when you’re cranking the wheel a lot as you would backing a trailer into an unfamiliar campground or picking your way along a difficult off-road trail, the steering fluid will heat up.


Oil, of any type, has a heat point at which it begins to break down. When that happens, mechanical problems manifest themselves at an alarming rate. That is why auxiliary coolers have good benefits.

Vehicle manufacturers and oil companies say the ideal operating range for non-synthetic engine oil is between 180°F – 200°F.

While operating within this range, oil does its job lubricating, cleaning and cooling the parts. Synthetics have a higher heat tolerance, which is why many owners of heavy towing vehicles have made that switch.

Hayden, one of the manufacturers of aftermarket engine oil and ATF coolers, says engines without coolers generally run with radiator coolant temperatures between 200°F and 220°F with oil temperature ranges between 20°F – 75°F hotter depending on the conditions.

(You’ll find this the case with most newer gasoline vehicles, with diesels running slightly lower temperatures.)

In other words, when the engine is performing flawlessly, the engine oil could already be in an early stage of overheating. If those temperatures go higher, for whatever reason, then real problems arise.

Perma-Cool, another well-known name in aftermarket coolers, says automatic transmissions generate large amounts of heat, too, and, unlike the engine, are totally dependent on the transmission fluid for cooling.

“When the fluid temperature exceeds 225°F the fluid deteriorates rapidly, diminishing its ability to lubricate and cool critical valves, springs, seals and other internal components, leading to premature failure and costly repairs,” warns a Hayden representative. “Over 90% of all automatic transmission failures are caused by overheating.”

Perma-Cool, Hayden, B&M, TCI, and a number of other manufactures claim that a 20° drop in fluid temperature can double the life of the transmission.

TCI transmission temperature chart.TCI transmission temperature chart.


The idea of engine and transmission oil coolers is to prevent—or delay—oil from getting to that critical break-down point.

Oil coolers, whether engine or transmission, work on one simple principle: hot lubricant is circulated through a series of copper, brass, aluminum, or other good heat-conducting tubes that radiate the heat out to fins that are directly in the path of ambient (generally cooler) air flow.

As the hot oil passes through the maze of cooling tubes, its temperature drops. In fact, some coolers can drop oil temperatures as much as 30-degrees depending on mounting location, application, and vehicle speed. The cooled oil then flows back to whence it came and the cycle repeats.

The factory-installed coolers that come as part of a pickup or SUV’s “tow package” option do that quite well handling the heat


 According to former Indy car mechanic Dave Bowman, regular fluid and filter changes are vital to keeping automatic transmissions trouble free.

Now employed as a vehicle-care expert for Allied Aftermarket Division (suppliers of Fram, Bendix, and Autolite parts), Bowman says that ideally the fluid and filter in an automatic transmission should be changed every two years or 24,000 miles, particularly if the vehicle is more than five years old.

However, Bowman and other vehicle experts warn that by-the-book service is not adequate if you drive hard, tow a trailer, go off-road, or haul a camper. 

In addition to checking transmission fluid levels frequently and having regular fluid and filter changes, the installation of an automatic transmission fluid cooler can go a long way towards increasing transmission life because it helps keep fluid temperatures out of the danger zone.

You might think that by having a transmission cooler installed and by performing regular preventive maintenance that your transmission worries are over. Not quite.

Even with the addition of a heavy-duty cooler, fluid temperatures can rise to dangerous conditions under certain conditions, such as when towing a heavy trailer up hills during the summer.

That’s why it is important to keep an eye on transmission fluid temperature while you are driving, which means that the installation of a transmission temperature gauge is a vital part of making sure your transmission stays healthy. 

If you notice fluid temperatures are rising, pull over and let the transmission cool down before it reaches the danger zone. Just make sure that when you pull over, you put the transmission in “Park,” set the brake and let the vehicle idle for a bit so the fluid circulates through the system as it cools down.

Shutting the engine down immediately will allow “heat sinking” of the fluid to occur, which can spike fluid temperature and cause the very  overheat damage you were trying to avoid cooking the parts. – BWS  

stresses brought about by heavy towing or hard off-road —at least well enough to see the vehicle’s engine and automatic transmission beyond the warranty period.

Aftermarket, auxiliary engine oil and automatic transmission fluid (ATF) coolers, more efficient radiators and electric fans are added lines of defense against overheat situations.

Upgrading older trucks with such items greatly extends, or possibly eliminates any oil- or ATF-related mechanical failures long after the warranty periods have xpired.

Transmission engineers and cooling specialists say that a 20-degree drop in fluid temperature can double an automatic transmission’s life.

This is especially important if you tow or carry heavy loads, or take to the off-pavement driving on a regular basis.


But adding an auxiliary cooler doesn’t mean much if it isn’t installed correctly. Just like in real-estate, location determines value when it comes to aftermarket coolers.

The key to any oil cooler’s efficiency is placing it in a location that provides the best flow of cool air across the cooling fins.

If there’s no room to mount the cooler flush against the radiator, check for a safe mounting location behind the bumper or other location exposed to a flow of fresh air.

(Stacking one cooler atop another is the least efficient way to utilize them.)

Some of the latest high-tech coolers, such as those from B&M, are thin in design and incorporate a built-in fan with thermostatic control.

That way you can mount the cooler in more locations and still have good cooling capacity because it provides its own air flow.

So, if you do a lot of trailer towing and want to take every measure you can to make sure your tow vehicle lives a long, healthy life, let cooler heads prevail—install an engine oil and ATF cooler in addition to the factory ones.


BD Diesel Performance

Canada-based BD Diesel Performance is a world-class manufacturer that designs and builds its products in-house for distribution Worldwide for North American Diesel vehicles.  One of their specialties is products designed to keep engine and transmission heat in check under the most severe conditions.  

B&M Racing & Performance Products

B&M Racings offers performance-oriented products including heavy-duty engine oil and transmission fluid coolers (vehicles up to 19,000 GVW), deep dish transmission pans (extra fluid equals lower temperatures) and other related cooling products.

Derale Cooling Products

As the company’s name states, Derale Cooling Products specializes in all aspects of cooling, including engine oil, coolant, and transmission. Products include electric cooling fans, clutch fans, transmission coolers, engine oil coolers, power steering coolers, frame coolers, transmission pan coolers and combination coolers.

Flex-A-Lite Consolidated

For over 36 years, Flex-A-Lite has been known as a manufacturer of quality high performance belt-driven and electric engine cooling fans, engine and transmission oil coolers, and accessories. They offer a complete line of products for automotive, light truck and heavy-duty applications.

Hayden Automotive

Hayden Automotive has long been known as a manufacturer engine and transmission cooling products from clutch fans to oil coolers and transmission fluid coolers. They offer models for nearly every heavy duty engine/transmission combination currently on the market.

Northern Radiator

This Minnesota-based company has been manufacturing radiators and transmission coolers for over 30 years. They produce product for agricultural, heavy-duty truck (semi), racing and offer coolers to fit most cars, pickups and SUVs.


One of the industry leaders in engine fluid cooling, Perma-Cool offers a complete line of  light- and heavy-duty transmission coolers, engine oil coolers and power steering fluid coolers, plus frame rail coolers, gauges, electric fans, remote oil thermostats and other accessories vital to lowering operating temperatures on tow vehicles.

TCI Automotive

TCI uses their 35+ years of on-track and heavy duty towing applications experience to specialize in building automatic transmissions and related products. Those products include a proven line of transmission and engine oil coolers, fan kits and gauges.