TH400 temp

I would like to know the optimum temp range for the th400. I know heat is bad for them but is too cold also a concern? I put a big cooler in front of my radiator and wondered if I should cover some of it when I plan on driving in temps below freezing. I also thought possibly MPG could be affected with cool fluid. So far I haven't noticed any difference in the operation of the transmission this season after the cooler was added.
Thanks

2deuce said:

I would like to know the optimum temp range for the th400. I know heat is bad for them but is too cold also a concern? I put a big cooler in front of my radiator and wondered if I should cover some of it when I plan on driving in temps below freezing. I also thought possibly MPG could be affected with cool fluid. So far I haven't noticed any difference in the operation of the transmission this season after the cooler was added.
Thanks

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add a temp gage. i have one on my duramax-allison combo and i like it. should never go over 190f. heat kills. i dont know if cold kills or not. thanks. mark

Looks like 175 is minimum temp.



There's More To Coolers Than You Think: It's no secret that heat kills automatic transmissions. And in high-performance street-strip applications, the problem is especially acute. Small diameter torque converters coupled with stop-and-go traffic greatly increase the heat level in an automatic transmission. In most cases, the extra performance heat under the hood can have the same effect as heavy loads, trailer towing and desert conditions.
How hot is too hot? The ideal operating temperature for automatic transmission fluid is between 175 and 225° F. At approximately 240° F, important additives in the ATF begin to cook. The result is the formation of varnish inside the transmission. At approximately 260° F, internal transmission seals (which are typically manufactured from a polyacrylate material) begin to harden. The end results are leaks, both internal and external, simply because the seals lose their elasticity. At approximately 295° F, transmission clutch plates begin to slip because the oil is breaking down further. At approximately 315° F, seals and clutches effectively burn out. Carbon forms in the oil and for all intents and purposes, the transmission is junk. Just for your information, a typical transmission will die within 2000 miles if subjected to 300° F+ heat.

Thanks for the heat breakdown and the best operating range. I want to put a temp gauge on my blazer, but where should it be located? I used a AC condenser for the cooler. Its big and cools alot I'm sure, maybe too much this time of year. I drive my blazer to work and the trip is 4 miles and about 5 or 6 minutes. The truck shifts fine but the trans temp probably never gets more than luke warm. I'm planning a 600 mile trip to include towing, what problems can low temp ATF cause?
Thanks

I have a factory temp gauge on trany of my 05 2500hd and norm driving temp stays about the 100deg. and when its worked never seen more then 180deg. on the temp gauge I had a ac condensor used as trans cooler on a 81 3/4 ton truck with a built small block and a turbo350 trans I plowed snow with and pulled at truck pulls in summer and never had any problems so you should be fine.

The truck never seems to have any issues shifting whether hot or stone cold. Although I'm never pushing it when the engine is cold, I could be working it hard while towing with the engine at operating temp but the trans still cool. I'm going to install a temp gauge. Is there an ideal location for it?
Thanks

Other places, other experts, have suggested the temperature sensor should be in the pan. This should indicate the temperature of the oil that the transmission has to "work" with. But, that might not be reflecting the maximum temperatures the oil is reaching as it works through the system.

I'm running a TH400 in my '56. All of the cooling is done with an external cooler. I also installed an external filter/housing and a thermal bypass valve in the outlet line that goes to the cooler. The bypass doesn't allow fluid to go to the cooler until it reaches 175 degrees. My temp sender is mounted in the external filter housing and pretty much gives me a direct reading of the heat generated by the transmission at the moment. I'm going to mount another temp sender in the transmission pan to give me an idea of the fluid temps prior to entering the pressure circuit.

Hopefully, you plumbed your external cooler inline with the internal radiator cooler. The internal radiator cooler is pretty efficient and will help to bring the trans fluid up to normal operation temps on those cold days. If I were going to pick one location for the sender, it would be located in the pan.

Smitty

Trans Temp

2deuce said:

I would like to know the optimum temp range for the th400. I know heat is bad for them but is too cold also a concern? I put a big cooler in front of my radiator and wondered if I should cover some of it when I plan on driving in temps below freezing. I also thought possibly MPG could be affected with cool fluid. So far I haven't noticed any difference in the operation of the transmission this season after the cooler was added.
Thanks

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On the turbo 400 with the deep cucv pan and a added cooler by the time your fluid cycles your temp will average around 137 degrees, you will be fine with what you have done it will extend the life of your trans. Sure mountains, spinning in snow, heavey loads etc.... you can expect to see 190 temps in the 400. Heat is what causes failure in most units but the 400 is by far one of the best ever built!! We change our fluid over to Type F when we build our own but it is getting harder to get and of coarse that is just "OUR" preference. The difference is only the "weight" of the fluid mostly but it seems to take more abuse before breakdown. I'm NOT telling anyone to change to that by no means its just what I have done since I was 11 years old as I grew up in a transmission shop my Grandfather owned for 53 years here in Asheville NC.
Always Let your trucks engine and trans warm up as this is another key factor in long life as with any hydrolic or oil system it is very hard to push cold fluids thru little holes "so to speak" and causes pressures to increase beyond its capability..
Well thats enough of my 2 CENTS Worth !! LOL

Kevin

junkridge said:

On the turbo 400 with the deep cucv pan and a added cooler by the time your fluid cycles your temp will average around 137 degrees, you will be fine with what you have done it will extend the life of your trans. Sure mountains, spinning in snow, heavey loads etc.... you can expect to see 190 temps in the 400. Heat is what causes failure in most units but the 400 is by far one of the best ever built!! We change our fluid over to Type F when we build our own but it is getting harder to get and of coarse that is just "OUR" preference. The difference is only the "weight" of the fluid mostly but it seems to take more abuse before breakdown. I'm NOT telling anyone to change to that by no means its just what I have done since I was 11 years old as I grew up in a transmission shop my Grandfather owned for 53 years here in Asheville NC.
Always Let your trucks engine and trans warm up as this is another key factor in long life as with any hydrolic or oil system it is very hard to push cold fluids thru little holes "so to speak" and causes pressures to increase beyond its capability..
Well thats enough of my 2 CENTS Worth !! LOL

Kevin

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best fluid choice would be some type of synthetic, mercon5 comes to mind, because of lower temps and better flow when cold over petro based. i use amsoil in my duramax-allison

I too use synthetic In my 08 duramax but the 400 friction plates and seals was not designed for that, there are companys out there selling the "wonder" fluids for the application but use at your own risk problems won't show up right away buy what I have seen from this was lip seals swelling causing them to go soft and in time a internal leak. I don't clam to be a expert on these but it seems I stay in the school of "hard knox" LOL. I learn something new EVERY day and it cost money to attend that school!!! Lesson learned?? Ha Ha.

junkridge said:

I too use synthetic In my 08 duramax but the 400 friction plates and seals was not designed for that, there are companys out there selling the "wonder" fluids for the application but use at your own risk problems won't show up right away buy what I have seen from this was lip seals swelling causing them to go soft and in time a internal leak. I don't clam to be a expert on these but it seems I stay in the school of "hard knox" LOL. I learn something new EVERY day and it cost money to attend that school!!! Lesson learned?? Ha Ha.

Click to expand...

The TH400 is a very robust transmission, in my opinion it is one of the best Turbo Hydros that was made, They will take more abuse than given credit for, We've used them in demo derbies with the coolers totally cut off and a steel loop from input to output, and have gotten them cherry hot to the point the pan gaskets are cooking, and after pulling them apart to use inother projects, they look decent.

They aren't meant for synthetics, the internal pressures are not high enough and the tolenences are not close enough to use synthetics, because they are just too slippery, they'll go for 200-300 k with proper DEX-3 changes and care.

In fact they shift better after rebuild using Mercon ( But Only After Rebuild Using Virgin Oil And Clutches!) which does not have as much friction modifiers in it, allowing the clutches to grab, instead of slip, Gm did allot of R&D to make these 400's shift like glass.

As far as the coolers you can do it a few ways, but I recommend you use it in conjuction with your radiator cooler, because you want some heat to keep the internals clean and the fluid from gumming up in the pan and servos, now I ran a TH-350 with the rad cooler totally out of the loop with just an RV cooler in front of the radiatir, but it was a 79 chev k-20 with an 1800 stall convertor and 40 in. mudders that generated enough heat.

Just My

There are alot of good posts on this subject here.

I have a M1008 that i did a 700R swap in and I have a temp guage in it to the pan, I was told the temp should be about 140-150 in the pan. I have a high volume pan with the heat-ribs, an external cooler inline with the radiator cooler. I live in Colorado and on long sustained climbs my temperature will start climbing and continue climbing until I stop (about 180-190degrees but would continue higher) and give it a few minutes rest, even if I just wait til the needle just starts coming back and then drive it will cool back down to 140-150, even if still climbing. I have put about 2,500 miles on the trany, but still have the inline filter in it, which may be part of the problem am I getting a clog somewhere? Any Ideas? Other than that the Truck runs great.

I bypassed the radiator cooler when I installed the ac condenser as a cooler because I thought that the radiator might get too hot, possibly over 190-200 on hot days and big loads. I was thinking of plumbing it so I could turn the radiator cooler off with a couple of valves. I have taken the truck on 2 300 mi trips with temps in the 20's without any observable differences in operation of the transmission. I should get a temp sensor on there to see what its doing.
Thanks

You will not have a problem Under ideal circumstances you would want no more then about 190 degrees. There are so many variables that you could see anything from about 160 degrees to 220 degrees and still be within the "safe" zone. trans fluid will take 275 deg heat before starting to break down I would not let it get over 250 for any amount of time to be safe if you find it getting close to 250 alot then just change the fluid more often to keep clean fresh fluid in it. you put a gauge in it I would bet you dont ever see 200 deg for norm driving!

I think a tach would help me out as well. Any good advice on that?

Also are there any interesting/important non-obvious driving techniques for longevity of the transmission?