Trans fluid question?

[rustystud]

Most all transmission heat comes from the torque converter. When the "stator" is freewheeling (fluid is basically a solid mass) there is not much heat generated. This occurs when the transmission is in final drive usually. The time it is making the most heat is when it is making the most torque (stator is not moving and fluid is spinning around and through the turbine and stator) . This occurs when your coming up through the gears. So if your engine is heating up at highway speeds, it is coming from the engine having to work harder with the overdrive and not the transmission.

 

[Drock]

Well I'm not much for math but I checked gear vendors final drive calculator and it says with the TH400 and 4.56 gears the final drive ratio is 3.56. I cross referenced that with a RPM calculator and I got 2773 RPM's at 70MPH. Now I don't know how much torque is needed or expended at that speed and rpm? Would I benefit from going to a taller tire sense our 6.2's make peek torque at 2000RPM's? Or is this simply a radiator problem?

 

[rustystud]

Well I'm not much for math but I checked gear vendors final drive calculator and it says with the TH400 and 4.56 gears the final drive ratio is 3.56. I cross referenced that with a RPM calculator and I got 2773 RPM's at 70MPH. Now I don't know how much torque is needed or expended at that speed and rpm? Would I benefit from going to a taller tire sense our 6.2's make peek torque at 2000RPM's? Or is this simply a radiator problem?

If your really overheating and not just a little hotter then normal then I would check the radiator. Our trucks should have the extra wide 4 core radiator. They can really take a lot of engine heat normally. So if your experiencing overheating then something is wrong there. If you do need to replace the radiator just a warning, this radiator will cost a pretty penny to replace ! I had to replace mine 4 years ago and it cost over $400.00 then ! Don't let them talk you into a smaller radiator though. You will regret it ! Hopefully it just needs a good cleaning and maybe a "rodding" . Our radiators are made with real heavy copper and brass so they can take a "rodding" while most new radiators cannot. Also while your in there replace the thermostat and the lower radiator hose. They tend to get overlooked. Also while it's apart take a look at the water pump. The vanes can come loose inside and then don't push any water. They won't leak, but they also won't help cool the engine.
Though I've only seen this happen 4 times in all my years of wrenching it can happen. You can check this by using a flashlight and looking into the pump and turning the pump shaft fast back and forth.
About going to a taller tire. You will just make the engine work even harder and cause more heat. Do you really drive at 70 mph all that much ?

 

[Drock]

If your really overheating and not just a little hotter then normal then I would check the radiator. Our trucks should have the extra wide 4 core radiator. They can really take a lot of engine heat normally. So if your experiencing overheating then something is wrong there. If you do need to replace the radiator just a warning, this radiator will cost a pretty penny to replace ! I had to replace mine 4 years ago and it cost over $400.00 then ! Don't let them talk you into a smaller radiator though. You will regret it ! Hopefully it just needs a good cleaning and maybe a "rodding" . Our radiators are made with real heavy copper and brass so they can take a "rodding" while most new radiators cannot. Also while your in there replace the thermostat and the lower radiator hose. They tend to get overlooked. Also while it's apart take a look at the water pump. The vanes can come loose inside and then don't push any water. They won't leak, but they also won't help cool the engine.
Though I've only seen this happen 4 times in all my years of wrenching it can happen. You can check this by using a flashlight and looking into the pump and turning the pump shaft fast back and forth.
About going to a taller tire. You will just make the engine work even harder and cause more heat. Do you really drive at 70 mph all that much ?

Well I haven't had a chance to drive it on the highway yet to see if this new pan and fluid change has helped. If it still over heats (210°). Then yeah I'll focus on the RAD. I found a few aluminum ones that look promising and I've had VERY good results with them on Hotrod projects. And yes I need to be able to drive this 70MPH just like any other truck. This is my daily driven work truck, and also used to haul iron furniture down the highway 500 miles per month... Is this smart?.. probably not LOL! But I like the truck and it impresses my customers. So I plan on doing whatever I can to make it reliable.

 

[o1951]

I would certainly get radiator rodded. Before doing more than the radiator, thermostat, hose and pump rot/ vane loss check, I would take truck to a trans guy I trust. The TH400 was a very popular civi trans. Just about any trans shop should be very familiar with it. Wouldn't hurt to check line pressures, modulator, etc. and make sure all is ok and spending more $$$$.

 

[rustystud]

Well I haven't had a chance to drive it on the highway yet to see if this new pan and fluid change has helped. If it still over heats (210°). Then yeah I'll focus on the RAD. I found a few aluminum ones that look promising and I've had VERY good results with them on Hotrod projects. And yes I need to be able to drive this 70MPH just like any other truck. This is my daily driven work truck, and also used to haul iron furniture down the highway 500 miles per month... Is this smart?.. probably not LOL! But I like the truck and it impresses my customers. So I plan on doing whatever I can to make it reliable.

I forgot to ask, but how does your transmission feel ? Does it seem to shift OK ? Have you felt it "slip" going into or out of gear ? If it is working fine then I would concentrate my efforts on the engine side ie: check radiator, water pump, hoses etc.

 

[Drock]

It runs fine, in fact when I pulled the pan it was super clean. No residue on the bottom of the pan and no metal on the magnet. As for the engine I replaced all the belts, hoses, and thermostat. And added a HMMWV crossover tube so I could mount the temp gauge probe correctly.

 

[Chaski]

Ever do a second check on your temperature gage? Maybe use an IR gun on your crossover? You may be chasing a ghost.

 

[rustystud]

Ever do a second check on your template gage? Maybe use an IR gun on your crossover? You may be chasing a ghost.

This makes a lot of sense. You need to mechanically check the temperature. You might just have a faulty gauge or sender. Or then again you could have a plugged radiator. But check it first.

 

[Drock]

I guess it could be a bad gauge, but there would be no way to test it with an IR gun because it cools off as soon as I slow down. And it only heats up on the highway, around town the temp its perfect at 195°.

 

[hatzie]

Set the IR gun next to you on the seat and run her up to "hot".
Pull over on the shoulder immediately and tag the engine etc with the IR thermometer right then.