maxxTORQUE | THE Magazine of the GM Diesel Community

The fish are in the freezer, and with that, it is time for my annual reel cleaning and vehicle servicing regimen; an oil change is always part of it. I am reminded of what that oil went through on all those fishing trips. It all started with a realization that my thermo-viscous fan should not be such a common occurrence. I seemed to fly effortlessly up steep mountain grades with my big camper load, on a 103ºF Arizona day, in air conditioned comfort, and in complete complacent silence, dreaming of bass boils. Then I awoke, eyes wide and startled, to the sound of a 747 landing on top of me… THAT FAN!

I wanted to silence that fan, and all heat issues its aural signature represented. I remember the first time I heard it, going 70 MPH on slight, rising terrain with NO load. On a 114ºF sunny day, it doesn’t seem to shut off. Adding insult to injury I know I am losing two to three miles per gallon whenever it is in full spin. I have heard the statement, “that fan is normal, be glad you have it,” a hundred times. I am glad. Glad I don’t have to believe that any more. What if I said that you are an oil overheater, and you have never seen it? Crazy am I? Do you have an oil temperature gauge? If you knew what your oil temp was when you towed through my back yard, you would own one. The oil overheats on every summer camping trip. Presently, oil is cooled indirectly at the stock engine mounted oil-water cooler. Oil heat must be conveyed to the coolant, then to the radiator, then to the atmosphere, making it indirectly cooled.

Below, you see the Stacked Plate Duramax Coolant-to-Oil Heat Exchanger. If it looks unfamiliar, you are looking at the side that fastens to the motor. The coolant passes over a series of plates which contain the flowing hot motor oil. On the far side (left), the filter thread is visible. This heat exchanger mounts to the driver’s side of the motor and houses the filter element. The oil inlet and outlet are the parallel ports on the bottom. The coolant comes straight from the water pump and enters on the upper right (not visible), and emerges at the large plate opening at the left.

Simplified, it looks like this: