Don’t miss out on 20% OFF all radiators! sale ends today!
Your vehicle’s radiator can do more than just keep the engine cool. There are two other fluids that your radiator may be keeping at the optimum temperature: transmission fluid and engine oil. If you have swapped an automatic transmission into your classic vehicle, you may have added an external cooler instead of using an internal cooler in the radiator. The same goes for an auxiliary oil cooler. While these certainly work to cool the fluids down, there are some major efficiency issues that can occur with external coolers.
The main concern with an external cooler is that there is no regulation of temperature. Wild swings in temperature can cause a whole host of problems that can reduce the life of your engine and transmission, along with a couple of other issues that you may not realize are happening. First, let’s break down the concerns for transmission and oil coolers.
Automatic Transmissions
All automatic transmissions require a cooler for the fluid, as heat kills a transmission faster than anything else. If the transmission temperature exceeds 230 degrees F, the fluid itself is toast as it forms a varnish. Above 250 degrees, the seals begin to harden, the clutches burn, carbon forms inside the transmission, and eventually the transmission fails. Keeping the transmission cool is important for a long life, but did you realize that there is such a thing as too cool? The optimum temperature for an automatic transmission is 175 degrees F, with an operating range of 165-220 degrees. Below 150 (depending on the fluid), the fluid is thicker than it should be, and you may experience harder shifts. Over time, the seals and valves can fail from being overworked by thicker fluid than they are designed for. Modern transmissions use a thinner fluid that is less likely to thicken at lower temps, but any transmission built before the mid-2010s is susceptible to this issue.
An internal cooler inside the radiator tank serves two functions- to cool the fluid while also maintaining an even temperature. Instead of your fluid cooling rapidly and recirculating, the fluid temp is kept within about 20-30 degrees of the engine temperature, ensuring that the fluid is within the optimal operating range. This is most important for stop and go driving. The goal is to reduce the temperature swings inside the transmission to regulate the overall temperature.
Oil Coolers
While most passenger cars don’t use oil coolers (high performance models often do), many trucks and SUVs utilize oil coolers to do the same thing as a transmission cooler, only the temperature regulation is even more important. When using an oil cooler, wide temperature swings can have a serious effect on your oil. The target temperature for engine oil is between 230- and 260-degrees F. Around 275 degrees Fahrenheit, conventional oil starts to break down, losing its ability to lubricate the engine. It goes without saying that this is very bad. Synthetic oil can handle much hotter temperatures, above 300 degrees. When the oil cools too much, it becomes much thicker as engine oil viscosity is highly reliant on temperature. Thicker oil means more drag on the moving parts, leading to premature wear. However, there is another critical issue that affects your engine oil, and it has nothing to do with lubrication.
For every pound of fuel burned in the engine, about a pound of water is generated as a byproduct. This water ends up in the crankcase as condensation. The engine oil must be hotter than 220 degrees in order for that water to boil out, along with other contaminants. If the oil cools too fast, and goes under 220, the water mixes with other combustion byproducts (namely sulfur), which forms an acid that eats the bearings and seals, eventually destroying the engine.
Engine oil requires a tight window to operate effectively, an external oil cooler can quickly reduce the oil temps far below the minimum 220 degrees, resulting in excessive wear and tear on your engine. An internal cooler in the radiator not only maintains the overall temperature of the oil, but also helps it get there faster.
Placement In The Radiator
You might be thinking, “My engine coolant temps are consistently below 220, how will an internal oil cooler help?”
The answer is in placement in the tanks. The oil cooler is typically installed in the hot side of the radiator, where the hot water comes out of the engine. This keeps the oil cooler as hot as possible to maintain the correct oil temperature. For transmissions, the cooler is located on the cool side of the radiator, after the engine coolant has run through the radiator core. This results in a cooler transmission temp, typically 10-30 degrees lower than the engine operating temperature.
Advertisement
Why Not Both Internal And External?
There are certainly applications where you may need to run both internal and external coolers for a transmission such as heavy tow vehicles. If your transmission temps are exceeding the 220 degree range, adding an external cooler can help bring it down. If you determine you need an external cooler, the optimum placement of the cooler is after the internal cooler. This can be done with a finned tube-style cooler mounted on the frame rail under the vehicle or a typical square cooler. By using the internal cooler first, your transmission fluid temp is regulated and the cooled further, sending the coolest fluid to the transmission, reducing the overall temperature. In most cases, dual coolers are not necessary.
Radiator Stack-Up
The final reason we recommend internal coolers is for overall efficiency. In most installations, the radiator is closest to the engine, with the A/C condenser in front of the core. Adding auxiliary coolers means placing them in front of the radiator. This not only means that the air flow through the radiator is significantly reduced, but there is also a lot more heat being pushed through the radiator core. The result is higher engine temps as the radiator needs cool air to exchange heat. If you have an intercooler, your radiator stack-up can get out of hand, resulting in overheating and inefficient drivetrain operation.
While ensuring that your transmission fluid gets cooled is the primary goal, how you get there matters in terms of efficiency and longevity of the transmission and the fluid. External coolers have their place, however in most cases, internal coolers offer the best of both worlds. If you need to switch up your auxiliary coolers, give U.S. Radiator a call at 800-421-5975 to discuss your needs and they will build you a radiator to serve your engine in the best possible way.