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Transfer Case Cooling:

As Bill mentioned I have an external cooler setup on my tcase. This came more out of necessity than anything else, since I developed a crack in my tcase cooling loop and could not justify dropping the tcase to replace a part which was poorly engineered to begin with. Instead I drilled and tapped both the drain and fill plugs fot the tcase. I will warn you that this is a rather difficult job without the proper tools since the plugs are case hardened and are VERY tough to drill. If you don't have a friend with a lathe (or at least a drill press) then buy a pair of aftermarket plugs from the auto supply store, they are usually just mild steel. After drilling the plugs, tap them for 3/8 pipe thread and install a pair of 3/8 nipples. Your lower plug will lead to an aftermarket fuel pump. I use a carter fuel pump from summit for this. It seems to work just fine, and has held up for about 6 months without any problems. There recently has been a few companies who make high heat pumps, but they are much more costly. Between my tcase and fuel pump I have installed a remote filter, which uses a simply spin on oil filter. This allows me to filter the fluid to a couple of microns, which is a vast improvement compared to the factory setup. Underhood I mounted a Perma cool oil cooler. It is about 5 inches wide and as long as the factory radiator. Summit markets them as Transmission coolers. I have this mounted at the bottom of the cooling stack, just above the power steering cooler. The inlet of the cooler is fed from the pump, the outlet side of the cooler run back to the fill plug of the tcase. Be sure to use automatic transmission hose for everything, NOT the cheaper fuel hose. Transmission hose is rated for the higher temps that your tcase runs at. I used 3/8 hose throughout, as well as 3/8 brass fittings. I have a thermocouple installed inline which allows you to monitor the fluid temp in the system. I also suggest you install an on/off switch for the pump. It is not usually necessary to run the pump while at slow speeds or at initial start up, ie it takes about 10 minutes at 60 MPH before the tcase fluid is up to 130 degrees or so.

Vincent Loccisano


Is this correct? Are you sucking the fluid thru the filter? Or should the filter be after the pump? We should put the temp guage immediately out of the case, right. Also, in place of the on/off switch, how about a thermostat that would still allow the pump to filter the fluid and bypass the cooler below 180 degrees. The guy in my local speed shop did not recommend a thermostat (in this case for the transmission) because he said, unlike engine oil, you want to keep the fluid as cool as possible (ie. no downside to too-cool fluid). Did you cap off the transmission fluid loops (vampires)?

Scott, 4DHT

One basic principle is that, Hot fluid should go directly to the filter, because Hot fluid filters more effectively. Therefore the pickup comes from the t case sump to the filter (with a temp sensor) to cooler to the pump (pump is pulling in cooled, filtered fluid) to the fill plug or old vampire circuit higher up.

Personally, I dont think the pump needs to be run all the time. In winter NE- my tcase rarely gets over 180. Would be nice to run the fluid through the filter every so often, however. Summer is another story. A thermostat operated pump would be nice--as i see it.

My question is,, would a check valve be helpful in this circuit?? I think not since the circuit does not run through sequential capillary-like channels as the trans does which is more air bubble sensitive.

Michael Selig

Question :

I recently installed a temp sensor in the drain plug for my Tcase, the length of the plug is aprox 1 inch the sensor only protrudes through the plug for about 1/4" to the inside of the Tcase. However, there is about 1/32 inch space around the sensor inside the drain plug before the threads end. I have not had my truck under load yet, but the Tcase temp just starts to come up off the peg around town.

How will this mounting arrangement effect the accuracy of my temp reading ? Any ideas ?


Hi Ron; That is just what my 93 reads. This transmission and transfer case heat thing seems to vary widely from truck to truck, or maybe it is year to year. I installed Datcon 140-320 deg. gauges in mine and the temps run so low and the cooling is so good that the guages rarely move off the peg. The usual temp is around 135 deg. If I push the truck on the highway for a while with a load it will come up some, but I think I should have bought the gauge with the lower range, 100-280. I just drained the fluid the other day after 20,000 miles and it looked brand new, and that was including some heavy duty driving in deep sand on the beaches. At first I didn't believe the gauges after reading the posts on the lists but I verified the temps by other instruments to satisfy my curiosity. I should just be happy with my 93 the way it performs I guess! They should have kept making the newer ones the same.

Glenn 93 4drht

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