Transmission temps. Should I be concerned?

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twigdog

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Jun 27, 2004
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Trans is GM TH400 in a ton truck. I just added an external filter and temp guage at my last oil change and flipped the $&*@ out. Normal temp is around 220 and pushed 235 with a small load on the back the other day. Installed a large cooler yesterday with only marginal results. 190 degrees on my way to work this morning and 220 again on my way home with an 800lb bale of hay this afternoon. I do a lot of heavy towing with this vehicle, up to 10,000 lbs. Can't wait to see what it does then. Anyway, the fluid I drained when changing had 17,000 mile on it and showed little to no degradation. Runs fine and shifts fine. Should I be worried?
 
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I don't know how similar the 400 is to the 4t60 front wheel drive tranny. However my trans [censored] out with a external trans filter. My trans guy said he wouldn't put a tranny in my car unless he could take the spin on filter off. He said the pump in my tranny wouldn't be able to push fluid through the spin on filter, the radiator, and the aux cooler I had. So having said that, I would consult with a local tranny shop.

Maybe look into the Magnefine inline filters. Many use them on this forum and like them.

some pics of a Magnefine cut open
 
"According to the Automatic Transmission Rebuilders Association (1) 90% of all transmission failures are caused by overheating, (2) if fluid temps can be held to 175°, ATF will last almost indefinitely, and (3) as a rule of thumb, every 20° increase in operating temperature above 175° halves the life expectancy of a transmission."

So is it more important to know what the fluid temp is entering the trans of how hot it is coming out? Seems the out temp would be more true to what the trans is experiencing. I'm new to the whole trans temp thing. I've always just changed around 25,000 miles and never put any thought into it. It's just that my filter came with a sending unit and now I'm paranoid. Like I stated earlier, I've done a lot of towing with no ill effect.
 
Maybe I should drop the cooler and just run what the General thought was appropriate for a 454 powered dually. It's a 350 these days though. Got tired of 7 miles to the gallon.
 
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Different vehicle, but my trans temps don't seem to go above 180, even towing and driving the living poo out of it. It has a factory cooler.

What kind of cooler did you use? There are different types, and some are vastly more efficient than others.
 
Ok. I feel better now.

OIL TEMPERATURE MEASURE AT CONVERTER OUTLET TO COOLER
350 degrees F is the maximum temperature. This is the normal place to install a temperature
gauge or signal. The temperature in this location will vary significantly with each vehicle startup
or hill. If the temperature reaches 350 degrees F, reduce throttle. To lower the transmission
temperature with the transmission in NEUTRAL, run the engine at 1,200 RPM for 2-3 minutes
to cool the oil. DO NOT allow the converter outlet temperature to exceed 350 degrees F.

OIL TEMPERATURE MEASURED IN THE SUMP OR OIL PAN
"¢ 150 degrees F – Minimum operating temperature for continuous operation.
"¢ 180–200 degrees F – Proper oil level checking temperature
"¢ 200 degrees F – Maximum oil level checking temperature.
"¢ 285 degrees F – Maximum sump/oil pan temperature for short duration, such as a long hill climb.
"¢ 300 degrees F – Metal parts inside transmission begin to warp and distort in varying degrees, seals melt rapidly and transmission fluid life is extremely short due to oxidation and distress.
 
OVERK1LL,

It's a tube and fin style. I had add a pint of fluid after installation.
 
Do not get rid of the cooler, whatever you do. The highest fluid temp will usually be the fluid exiting the transmission (from the torque converter) and before it gets to the cooler(s). The THM400 does not have a lock-up converter IIRC and so is always in the converter slip mode (which builds heat in the fluid) while pulling. 220 deg F where your temp sender is located, is fine. The fluid in the pan is probably a good 20-40 deg cooler.

beast3300: your FWD transxle probably did not die due to the external filter. If there is any question about adequate flow in the cooler circuit, I just take the line loose that is returning fluid back to the transmission (after the coolers and filter), and start the engine and check the flow. This is actually part of how I flush a transmission to get a complete change, anyway. What could be more simple? If it is just barely flowing, then there must be some restriction such as a blocked cooler or filter or kinked line/hose. I have done nothing but extend the life of many transmissions AND the fluid with aux cooling and filtration. Very worthwhile upgrades, IMO.
 
The torque converter produces most of the heat, and is the last thing before the cooler output. The temps there are a good bit hotter than what most of the tranny sees.
 
Final question. Should the fluid be routed through the radiator first and then the cooler, or through the cooler and then radiator to stabalize the temp?
 
It doesn't matter, it is all a cycle.

You need to make sure that you don't take the heat exchanger in the radiator out of the loop.

On very cool days, it will help to warm the transmission fluid up to operating temperature.

You want to measure the transmission at the hottest point (where it is leaving the transmission), you can do this using the obd2 port also.
 
My experience on another older GM truck was that the radiator could consistently take 40 degrees off the trans temp regardless of ambient temp (senders mounted on both side of the cooler and in the pan). The oil to air cooler was more subject to ambient temp (greater temp differential=more effective) so wasn't as consistently effective in very hot weather but VERY effective in cold. If my cooler out line was 225, pan temp was only 170. Tried it both ways and in the end, I left it going through the rad first. In the winter (I lived in W. Colorado where it's 100+ in summers but 30F in winter) it sometimes overcooled a bit(it was a big cooler) and ended up under 150 pan temp. I could bring that up by reversing the flow. That was relatively easy to do on my setup and I did it for a while but later just covered the oil to air cooler in cold weather.

Anyway, your temps are right in line with normal, so I wouldn't be sweating at all.
 
Personally, I'd run radiator first, then aux cooler. That's how I run the cooler on my Jeep, as well as how it was set up for those that had a factory aux cooler. It gives maximum cooling under heavy load.

In cool weather, I know I'm overcooling mine badly, but it doesn't shift any differently or anything. I haven't gotten a gauge on it yet, but after driving for about 20 mins in 40* weather, I can usually put a hand on the tranny pan, and it's hot, but not uncomfortable to the touch (probably around 120 - 130).
 
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I have a friend who is running a souped up 4r70w transmission with a 4000 stall converter on a weekend racer ford.

He measures oil temp from the obd2 port which I beleive is pulling it from inside the transmission.

He added a very large stacked fin cooler (about the size of a volkswagen radiator).

His temperatures go from about 140 to 170 on very hot days.
 
One of the determining factors while using a fin/tube type cooler is temperature differential driving force. The higher the temperature the more efficient the cooler will operate. Locate the cooler at the highest temperature point--within practicality of course. John--Las Vegas.
 
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