urbex
1/2 ton status
You can disagree with the laws of physics all you want, but it won't change the fact that liquid is far more efficient at transferring heat than air, period.
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Trans temp?
- Thread starter dangerdog
- Start date
You can disagree with the laws of physics all you want, but it won't change the fact that liquid is far more efficient at transferring heat than air, period.
Thats why a radiator is so big. It needs all that surface area to remove the heat to the air.
beags86
Eastbound and Down
No, I'm not arguing that. It the idea of a rad cooler vs a stand alone.
If a rad cooler has a 190 stat in it the engine is going to run at 190.
If I use a stand alone on a cold day I'm not limited by that. Meaning maybe the trans could be cooled to 160, etc,etc. A rad would never allow that.
I think you want the fluid to hit 210-220 to boil off any condensation though.
79rustyk10
3/4 ton status
My issue with this whole argument, is, isn't trans temp supposed to be relatively close to engine temp, once both are warmed up of course? While yes the radiator cooler warms the fluid to some extent, in theory it also removes some heat on the other end of the spectrum. So technically wouldn't the fluid temp be stabilized by the radiator cooler, and cooled by the auxiliary cooler?
beags86
Eastbound and Down
I wonder this all the time. How cool it to cool for the trans temp?
The radiator takes the "big" heat out then it goes into the aux cooler and it cools down below the thermostat temp.
How cool should it go? 160? 140?
I don’t know how cool is too cool on the post cooler side. I think it would be best to measure the temp coming out of the trans before the cooler and try to keep it under 220. ?
I have a temp sender for my 700R4 in the pan, behind the big block. It takes a LONG time of regular driving to get the trans to get anywhere close to engine temperature. This is with no external cooler, only the one in the radiator. The radiator is usually cooler than the engine temperature, since it is doing its job. The only time I have gotten the trans to heat was lots of 2nd gear, low range playing around at 12K elevation while screwing around. And I only saw 220* and then I backed off.
And I agree that it takes some temperature to cook off condensation, the lower the temperature, the longer it takes.
I have looked at the shop truck , ('07 GMC, 6.0, 6L90) with both factory coolers and I don't think that I have ever found temps over 190*. But it doesn't pull much weight, just some highway and in town driving.
And I agree that it takes some temperature to cook off condensation, the lower the temperature, the longer it takes.
I have looked at the shop truck , ('07 GMC, 6.0, 6L90) with both factory coolers and I don't think that I have ever found temps over 190*. But it doesn't pull much weight, just some highway and in town driving.
red EOD
1/2 ton status
Ideal temp for hydraulic fluid (what ATF is based from) is 140-165F. Obviously maintaining just the ideal range isn't going to happen but it's the best target to aim for.
The other thing you might consider is the water temp shown on the gauge is taken at the side of the head or on the top of the intake manifold where it is at it's hottest, 190-200. The water in the radiator is/has been cooled and thus cools the trans fluid more then you think. The temp of the fluid coming out of the torque converter is a lot hotter then the fluid sitting the the pan and a lot hotter then the 200 degrees in the radiator.
If you want to cool a red hot piece of metal(or hot liquid) after welding what does that quicker? Blowing air across it or dunking it in water?
But hey, in the end it's your truck so do whatever will let you sleep at night.
If you want to cool a red hot piece of metal(or hot liquid) after welding what does that quicker? Blowing air across it or dunking it in water?
But hey, in the end it's your truck so do whatever will let you sleep at night.
Last edited:
urbex
1/2 ton status
Except that the engine thermostat controls ONLY the minimum temperature of the coolant in the engine. It has absolutely zero effect on the temperature of the coolant in the radiator. Remember, for the radiator to be doing it's job, the coolant on the cold side of the radiator, where the trans cooler is located, HAS to be cooler than the coolant going into the hot side. If the engine is running at 190, than the coolant on the cold side of the radiator will be running around 180. If the cold side was at that same 190, the vehicle would quickly overheat as the radiator isn't pulling heat out of the coolant.
Contrary to popular belief, there IS a "too cold" point for automatic transmissions. Just like engine oil, the ATF will thicken at colder temps, causing less flow along with shifting and other oddities until it warms up. Anyone old enough to remember driving cars in the 50s and 60s in the colder northern states should be familiar with this - a car that's been sitting in sub freezing temps all night will have a transmission that behaves differently than a warm one. Modern electronic automatics deal with this much more elegantly with variable pressure control solenoids and electronic trans temp sensors.
However, you don't need the ATF to running at 200+ to "burn off moisture". It doesn't need to be boiled out of the fluid, only warmed enough to evaporate the water out. The kicker here is that the cooler temps just means it takes longer. Think of spilling water on hot concrete in the summer - takes only minutes (or seconds if you're in sunny, beautiful Phoenix
) for the water to evaporate off. This will happen fairly quickly even at fluid temps of 120-130. Getting back to the standalone vs radiator cooler, while in theory the standalone wouldn't be limited to minimum engine temps, it also wouldn't be nearly effective enough to cool that ATF down to 160 unless the trans cooler was the size of the engine radiator as well, due to the difference in efficiency of liquid to liquid coolers vs air to liquid. That's why they are sold as "auxiliary coolers" and not "standalone coolers".
Huh. Trying to find some actual testing on auxiliary coolers and routing, not much I could find.
I did find a guy that says he measured fluid temps, and running from radiator to auxiliary to trans, the fluid never got over 100* when ambient temps were around freezing.
Seems to me, assuming the radiator is adequate in the first place, the "safe" bet is to run the fluid through the auxiliary cooler, then radiator, then trans, to ensure the fluid gets warm enough, but still reduce the work the radiator has to do as ambient and/or transmission temps climb.
It seems the aftermarket manufacturers recommend running from radiator to cooler, but their only concern also singularly seems to be getting the fluid cooler, and that isn't going to help engine cooling, nor control minimum temp.
I did find a guy that says he measured fluid temps, and running from radiator to auxiliary to trans, the fluid never got over 100* when ambient temps were around freezing.
Seems to me, assuming the radiator is adequate in the first place, the "safe" bet is to run the fluid through the auxiliary cooler, then radiator, then trans, to ensure the fluid gets warm enough, but still reduce the work the radiator has to do as ambient and/or transmission temps climb.
It seems the aftermarket manufacturers recommend running from radiator to cooler, but their only concern also singularly seems to be getting the fluid cooler, and that isn't going to help engine cooling, nor control minimum temp.
urbex
1/2 ton status
The aftermarket is in the business of selling products the consumers want, not necessarily the same as what the consumers need or should/should not install. Most people are under the false belief that cooler is better, much the same that there are still MANY people think that installing a 160* thermostat is better for the engine, as once again - "cooler is better!", will solve an overheating problem, or the path to getting "free power" out of their motors.
Or, look at the recommendations often given when someone asks what size cooler they should add - "biggest one you can cram in there!". As opposed to the factory installed cooler that GM installed on my Suburban as part of the heavy duty cooling option - about 12 inches by 8 inches...
The answer to an overcooling situation is a thermal control valve - https://blog.oregonperformancetransmission.com/?p=571
What I'd like to see in testing is the outlet temp when the fluid is routed one direction or the other. There are variables that would need controlled for, but I've seen 30* claimed in temp reduction from an auxiliary cooler. I suppose under extreme cold conditions, trans fluid coming from the auxiliary cooler might drop engine temp, thus the valve.
Running it through the radiator last should generally keep the fluid within a pretty narrow temperature range without needing a valve, whereas running it through the auxiliary cooler last will have the fluid temp subject to ambient conditions.
I believe I still have the directions for the "factory" dealer add-on, fan-less transmission cooler for the squarebodies, no idea if GM spent any time working that out, or if it was before they really worried about trans temps. I'll check what they suggested for routing back then.
Edit: So FYI, they used the worst ink ever when they printed the instructions for it. Can't read half of it anymore. The cooler assembly appears to be part number 14032772, and the cooler itself may be 3027982. The instructions only have a diagram to show where to cut the factory lines, it shows the cooler spliced into the line that goes to the lower radiator fitting, whatever one that is, inlet or outlet, I don't know. And that assumes the somewhat hard to make out diagram is correct.
Last edited:
red EOD
1/2 ton status
Most factory applications have the radiator first then stand alone cooler for a few reasons. Brings the fluid up to operating temp faster (all the fluids that pass through the radiator so trans, coolant, and engine oil in some applications). Having the stand alone oil cooler after brings the temps down lower than the engine coolant temps which is better for the oil. A temperature controlled bypass for the stand alone cooler would be a good option but isn't really needed for a transmission because the reservoir isn't large enough to worry about getting the temp too cold and be a problem.
Temp probe location, take your pick just be familiar with what the max safe temp should be (chart on the first page is a good quick reference). If it's returning to the pan at 140F under operating conditions then that's basically perfect.
Temp probe location, take your pick just be familiar with what the max safe temp should be (chart on the first page is a good quick reference). If it's returning to the pan at 140F under operating conditions then that's basically perfect.
beags86
Eastbound and Down
Back in the 90s my old man owned a 15 quick lube. With that we "flushed" auto trans.
We popped the cooler lines and a hooked a machine to push the old fluid out. Around the same time is when dodge/Jeep was notorious for dropping auto transmissions.
For some reason people thought that buying a aux and bypassing the rad was the thing to do to save them from Chrysler's wrath. (Personally I recommended a full auto trans service with a side of trade off at the Chevy dealership
)Anyway I personally had serviced hundreds, if not thousands, of trucks and Jeep's that had the rad cooler bypassed.
I actually took the time to tell the people that it needed to be changed back. And actually we documented it. Due the fact that people would have their trans start slipping then get it flushed thinking it would fix it, or wanting us to work on it so they could sue and get a transmission after it blew up a few miles out of the shop door. The fact that a trans cooler had been modified saved my old man from buying several transmissions. It doesn't hold up in court.
I think it is in the pressure side. Have to check.
You can use a toggle switch (or rotary selector or whatever) to display multiple temp senders on a single gauge. Then you can install temp senders in as many places as you're curious about.
The correct temp with today's modern transmissions is much different than even 10 years ago. My 17' Super-duty runs at 200+ normal and goes up to 240 towing and I've seen higher. But I also see 230 water temps etc. Today's engines and transmissions have much better seals and hard parts to withstand higher temps. Modern Synthetic fluids go hand in hand with these changes and temps too, 230 isn't hot anymore basically.
When your dealing with the typical older TH400, Th350, 700R4 stuff it's probably best to stick with the older conventions of 200 degrees is pretty hot and 180 is a great operating temp. You can have better seals etc. installed in any of these transmissions and you can then change your thinking up to 200 degrees being normal and 230 being hot provided you have the right fluid.
Running good hard parts, seals, and Amsoil slick shit racing fluid I don't really mind seeing 230+ degrees with my Buggy. We've seen 260+, continued on racing and the report on tear down was that things were totally fine.
Liquid to Liquid heat exchange is far superior to air to liquid, most higher endurance vehicles use many liquid to liquid heat exchangers and up-size the rad. to match. Air to Liquid exchangers have much higher failure rates because they have to be out in the open, a heat exchanger can be buried in the depths of the vehicle and it's design is very durable. It's not uncommon to see engine oil, power steering fluid, transmission fluid, even dif fluids all have a heat exchanger and 1 massive radiator to handle all the heat load on a Desert race vehicle,
When your dealing with the typical older TH400, Th350, 700R4 stuff it's probably best to stick with the older conventions of 200 degrees is pretty hot and 180 is a great operating temp. You can have better seals etc. installed in any of these transmissions and you can then change your thinking up to 200 degrees being normal and 230 being hot provided you have the right fluid.
Running good hard parts, seals, and Amsoil slick shit racing fluid I don't really mind seeing 230+ degrees with my Buggy. We've seen 260+, continued on racing and the report on tear down was that things were totally fine.
Liquid to Liquid heat exchange is far superior to air to liquid, most higher endurance vehicles use many liquid to liquid heat exchangers and up-size the rad. to match. Air to Liquid exchangers have much higher failure rates because they have to be out in the open, a heat exchanger can be buried in the depths of the vehicle and it's design is very durable. It's not uncommon to see engine oil, power steering fluid, transmission fluid, even dif fluids all have a heat exchanger and 1 massive radiator to handle all the heat load on a Desert race vehicle,
