Can you over cool an automatic transmission? I am changing from an in the radiator tank cooler to an external air/oil cooler. I have always been of the thought that the cooler the trans is, the better. Am I totally off the ball? I have some area in the fender behind each fog lamp to mount a cooler w/fan. I do not believe it would be an issue to have the fans come on at high temps, but what if I'm coming down the mountain with lot's of time cruising at speed ( with the fans off I would assume ) what could it do to my trans?
Overcool a transmission.
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you can easily install a thermostat in the cooler line.
Or keep the radiator cooler in the loop, that will put some heat into the fluid during winters and will remove some heat during really hot days.
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Short answer....Yes, you can overcool a transmission.
A tranny pulling a trailer thru the desert can use all the cooling it can get while a normal passenger car tranny in winter probably wouldn't warm up enough with a typical cooler installed.
Tru-Cool, Hayden and other make an LPD (low pressure drop) line which bypasses cold fluid.
A tranny pulling a trailer thru the desert can use all the cooling it can get while a normal passenger car tranny in winter probably wouldn't warm up enough with a typical cooler installed.
Tru-Cool, Hayden and other make an LPD (low pressure drop) line which bypasses cold fluid.
It would only be "overcooled" in a winter situation. In warmish weather there isn't much danger of that. IMO, "overcooling" is a remote possibility that most of us don't need to worry about. It's usually too much heat that causes worry. Still, to give the subject some consideration, I see it from two perspectives.
1) Viscosity. The trans is designed to operate most of the time with the oil at a specified viscosity ( just like the engine). When the oil is very cool, it will be significantly thicker and trans operation will be altered to some degree. That could make for harsher shifts and an increase in fluid friction that could decrease fuel economy to some small degree. There are mechanisms in the trans to moderate such effects but the trans was still designed for the oil to be at a specific viscosity (again, just like the engine).
2) Moisture. Moisture buildup is possible in an automatic and, just as with an engine, if it isn't baked out by the heat of operation, bad chemical reactions start to happen and damage can result. The very few times I've heard of problems in this area, and I had the 3rd degree the info out of a lot OE engineers and tranny repair specialists, it happened to people who short-hopped a lot in very cold climates. It's not a common problem but a possible one for some people.
My advice is to monitor your trans oil temps by installing a gauge and add whatever cooling solutions are needed. You want the fluid to warm up to normal temp (150-180F-ish) and stay that way no matter what. Some vehicles don't need any help to do that and some sort of gauge will help you know that. If you are in Las Vegas, you may be one of the few people who won't ever have to worry about overcooling, or at least only for very short periods.
The PCM in some cars will read trans temp and using monitors like the UltraGage or ScanGage (google them and check their application and features according to your cars), you can plug it into the OBDII port and monitor a whole bunch of engine and powertrain parameters.
You can install a regular analog gauge too. I assume your cars are those listed in your sig. I don't know those cars at all but assume they have acooler and cooler lines. FWD cars are often difficult to fit a gauge sender into the trans itself, but you can install them into the cooler lines.
Bear in mind that the temp reading you get from an automatic will vary according to the placement of the sender. It will read moderately cool in the pan... that's the "bulk oil" temp. The out line to the cooler will be the hottest, as it's bleed off from the converter. The return line from the cooler will obviously be the coolest. For experimental purposes, I had sensors in all three positions in my old diesel Blazer (700R4, a notoriously hot running tranny) and it was very interesting to monitor and see the differences. The pan could be at 180F, the out line at 240F and the return line 140F... all at the same time! The point is that you need to interpret whatever readings you get according to the sensor locale.
As to which is best? There are many schools of thought and I have vacillated myself. Since it's time-at-temperature that's the biggest cause of fluid oxidation, not those short high spurts of temp, I have gradually come to the conclusion that the bulk oil temp, in the main oil reservoir, the most useful parameter to monitor. You could make it work anywhere but if you only look at the out line, all you'll see are heart-stoppingly high temps from the converter. They will be highly variable too, only peaking when the converter is unlocked and you are working the trans. WIth the converter locked, the T/C is not generating much heat and you'll largely see bulk oil temps.The bulk temp is largely stable and increases and decreases very slowly.. making it a boring gauge to watch if you are into that (which I am!).
I wouldn't advise install any external cooler without a demonstrated need. You can only demonstrate that need with a temp gauge of some sort. Logic then dictates that a gauge is job one.
1) Viscosity. The trans is designed to operate most of the time with the oil at a specified viscosity ( just like the engine). When the oil is very cool, it will be significantly thicker and trans operation will be altered to some degree. That could make for harsher shifts and an increase in fluid friction that could decrease fuel economy to some small degree. There are mechanisms in the trans to moderate such effects but the trans was still designed for the oil to be at a specific viscosity (again, just like the engine).
2) Moisture. Moisture buildup is possible in an automatic and, just as with an engine, if it isn't baked out by the heat of operation, bad chemical reactions start to happen and damage can result. The very few times I've heard of problems in this area, and I had the 3rd degree the info out of a lot OE engineers and tranny repair specialists, it happened to people who short-hopped a lot in very cold climates. It's not a common problem but a possible one for some people.
My advice is to monitor your trans oil temps by installing a gauge and add whatever cooling solutions are needed. You want the fluid to warm up to normal temp (150-180F-ish) and stay that way no matter what. Some vehicles don't need any help to do that and some sort of gauge will help you know that. If you are in Las Vegas, you may be one of the few people who won't ever have to worry about overcooling, or at least only for very short periods.
The PCM in some cars will read trans temp and using monitors like the UltraGage or ScanGage (google them and check their application and features according to your cars), you can plug it into the OBDII port and monitor a whole bunch of engine and powertrain parameters.
You can install a regular analog gauge too. I assume your cars are those listed in your sig. I don't know those cars at all but assume they have acooler and cooler lines. FWD cars are often difficult to fit a gauge sender into the trans itself, but you can install them into the cooler lines.
Bear in mind that the temp reading you get from an automatic will vary according to the placement of the sender. It will read moderately cool in the pan... that's the "bulk oil" temp. The out line to the cooler will be the hottest, as it's bleed off from the converter. The return line from the cooler will obviously be the coolest. For experimental purposes, I had sensors in all three positions in my old diesel Blazer (700R4, a notoriously hot running tranny) and it was very interesting to monitor and see the differences. The pan could be at 180F, the out line at 240F and the return line 140F... all at the same time! The point is that you need to interpret whatever readings you get according to the sensor locale.
As to which is best? There are many schools of thought and I have vacillated myself. Since it's time-at-temperature that's the biggest cause of fluid oxidation, not those short high spurts of temp, I have gradually come to the conclusion that the bulk oil temp, in the main oil reservoir, the most useful parameter to monitor. You could make it work anywhere but if you only look at the out line, all you'll see are heart-stoppingly high temps from the converter. They will be highly variable too, only peaking when the converter is unlocked and you are working the trans. WIth the converter locked, the T/C is not generating much heat and you'll largely see bulk oil temps.The bulk temp is largely stable and increases and decreases very slowly.. making it a boring gauge to watch if you are into that (which I am!).
I wouldn't advise install any external cooler without a demonstrated need. You can only demonstrate that need with a temp gauge of some sort. Logic then dictates that a gauge is job one.
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Kestas
Staff member
I remember some old posts that addressed the possibility of overcooling. Transmission fluid operating temperatures are ideal at certain warm temperatures, not room temperature. To prevent overcooling, the cooler is mounted to cool the fluid after it comes out of the transmission, and before it enters the radiator. That way, if it cools too much, the fluid has a chance to warm back up to ideal operating temperatures, yet still cools down if it's too hot.
I'm continuously puzzled by the example of the car's radiator loop for setting a tranny to the "right temperature", as the (water) thermostat keeps the car rad very cold most of a winter. I'd expect the tranny itself has some sort of method of dealing with it (internal bypass thermostat etc) if overcooling were a concern.
It's tough to overcool an auto. Some newer computer controlled ones will try to warm themselves up, killing fuel economy. However, many (such as the one in my Jeep) really don't care much.
The only time it might be overcooled is highway cruising with the torque converter locked in the dead of winter , and even then, I've had no issues with mine (11x11x3/4" external cooler, rad cooler bypassed). When the converter is unlocked, it's making plenty of heat. I don't really like those thermostats, as 180* is warmer than most trannies need to run. If I could find a 150 - 160* t-stat for one, I'd install it. Otherwise, I don't want my tranny running 190* all the time.
After a highway run in the winter, the pan is lukewarm to the touch. Only if the fluid is below about 30* does the tranny feel weird (hangs in low gears, feels sluggish). Once the fluid warms up a bit (even if it's technically too cold), it shifts and drives normally. It shifts just a hair firmer with the fluid good and warm.
The only time it might be overcooled is highway cruising with the torque converter locked in the dead of winter , and even then, I've had no issues with mine (11x11x3/4" external cooler, rad cooler bypassed). When the converter is unlocked, it's making plenty of heat. I don't really like those thermostats, as 180* is warmer than most trannies need to run. If I could find a 150 - 160* t-stat for one, I'd install it. Otherwise, I don't want my tranny running 190* all the time.
After a highway run in the winter, the pan is lukewarm to the touch. Only if the fluid is below about 30* does the tranny feel weird (hangs in low gears, feels sluggish). Once the fluid warms up a bit (even if it's technically too cold), it shifts and drives normally. It shifts just a hair firmer with the fluid good and warm.
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sorry to disagree, but that is absolutely not true. The modern auto trans is designed for a very specific range of temps, and a cold start program ("hanging in lower gears) is just helping it up to where it should be.
Many cars have a thermostat or bypass already in there. The newer and more sophisticated the trans the more likely you are to find a thermostat.
For many of my street cars I have run modern autos like a 4L80-E with a stand alone controller, and it's own cooler and thermostat. Optimum temp IME is usually above 160-170 and below 190 degrees.
Many cars have a thermostat or bypass already in there. The newer and more sophisticated the trans the more likely you are to find a thermostat.
For many of my street cars I have run modern autos like a 4L80-E with a stand alone controller, and it's own cooler and thermostat. Optimum temp IME is usually above 160-170 and below 190 degrees.
Originally Posted By: rslifkin
The only time it might be overcooled is highway cruising with the torque converter locked in the dead of winter , and even then, I've had no issues with mine (11x11x3/4" external cooler, rad cooler bypassed). When the converter is unlocked, it's making plenty of heat. I don't really like those thermostats, as 180* is warmer than most trannies need to run. If I could find a 150 - 160* t-stat for one, I'd install it. Otherwise, I don't want my tranny running 190* all the time.
THAT'S an EXCELLENT point that I failed to address. I saw that with my old Blazer a few times cruising on I70 between Grand Junction and Moab in January. 120-140 temps on all three gauges. I think steady temps in that range are enough to clear out moisture, but the oil is definitely running closer to it's 40C viscosity.
The only time it might be overcooled is highway cruising with the torque converter locked in the dead of winter , and even then, I've had no issues with mine (11x11x3/4" external cooler, rad cooler bypassed). When the converter is unlocked, it's making plenty of heat. I don't really like those thermostats, as 180* is warmer than most trannies need to run. If I could find a 150 - 160* t-stat for one, I'd install it. Otherwise, I don't want my tranny running 190* all the time.
THAT'S an EXCELLENT point that I failed to address. I saw that with my old Blazer a few times cruising on I70 between Grand Junction and Moab in January. 120-140 temps on all three gauges. I think steady temps in that range are enough to clear out moisture, but the oil is definitely running closer to it's 40C viscosity.
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Most of the oil thermostats(earls, hayden, mocal, permacool, derale, canton, empi, holley....) are set to be fully open by 180F. From what I've seen, they start opening at 150-160F. And, regardless of the opening temp, many 'bleed' or leak about 5-10% even when fully cold closed. I definitely recommend a thermostat for those colder climates. A piece of cardboard on the front of the cooler during the winter also helps.
There also was a time when you can contact the thermostat manufacturer and they would 'set' the opening temp for you. Might want to give Mocal/BatInc.... a call or email.
There also was a time when you can contact the thermostat manufacturer and they would 'set' the opening temp for you. Might want to give Mocal/BatInc.... a call or email.
Steve - The only cold start warmup on mine is an OD and TC lockup disable below 40* fluid temp (it's a 46RE). Even in 5* weather, by the time I get 1/2 a mile, the fluid is past that. For the first few seconds, it hangs simply due to it not liking the thick fluid. By the time I make it 1000 feet from my parking spot, it's shifting fine. I have a friend with a similar tranny (42RE) that doesn't do the same, so it's definitely not by design. All but OD and TC lockup are mostly hydraulically controlled in my 46RE.
The more electronics the tranny has, the more it will care about running cold, in many cases. Simpler trannies typically won't care.
The more electronics the tranny has, the more it will care about running cold, in many cases. Simpler trannies typically won't care.
Originally Posted By: FusilliJerry82
http://www.perma-cool.com/Catalog/Cat_page14.html
That looks like a winner to me.
And thank you to everybody who posted!
http://www.perma-cool.com/Catalog/Cat_page14.html
That looks like a winner to me.
And thank you to everybody who posted!
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Originally Posted By: rslifkin
Steve - The only cold start warmup on mine is an OD and TC lockup disable below 40* fluid temp (it's a 46RE). Even in 5* weather, by the time I get 1/2 a mile, the fluid is past that. For the first few seconds, it hangs simply due to it not liking the thick fluid. By the time I make it 1000 feet from my parking spot, it's shifting fine. I have a friend with a similar tranny (42RE) that doesn't do the same, so it's definitely not by design. All but OD and TC lockup are mostly hydraulically controlled in my 46RE.
The more electronics the tranny has, the more it will care about running cold, in many cases. Simpler trannies typically won't care.
Believe what you want, but you're stating misinformation in your post.
Your 46re is hydraulically ACTUATED but electronically controlled. The computer is still running the show. Your cold start program raises your shift points, too.
The trans has its own fluid pressure modulator so the thickness of the fluid (within reasonable limits) does not affect the pressure much at all.
And finally, it's exactly the opposite of your statement, the more electronic controls your trans uses the LESS it will be affected.
Steve - The only cold start warmup on mine is an OD and TC lockup disable below 40* fluid temp (it's a 46RE). Even in 5* weather, by the time I get 1/2 a mile, the fluid is past that. For the first few seconds, it hangs simply due to it not liking the thick fluid. By the time I make it 1000 feet from my parking spot, it's shifting fine. I have a friend with a similar tranny (42RE) that doesn't do the same, so it's definitely not by design. All but OD and TC lockup are mostly hydraulically controlled in my 46RE.
The more electronics the tranny has, the more it will care about running cold, in many cases. Simpler trannies typically won't care.
Believe what you want, but you're stating misinformation in your post.
Your 46re is hydraulically ACTUATED but electronically controlled. The computer is still running the show. Your cold start program raises your shift points, too.
The trans has its own fluid pressure modulator so the thickness of the fluid (within reasonable limits) does not affect the pressure much at all.
And finally, it's exactly the opposite of your statement, the more electronic controls your trans uses the LESS it will be affected.
Install the aftermarket cooler like they all recommend.
That is, IN lINE. IN SERIES with your present tank cooler.
The tank first, then the new one, then back to the tranny.
That is, IN lINE. IN SERIES with your present tank cooler.
The tank first, then the new one, then back to the tranny.
Originally Posted By: mechtech2
Install the aftermarket cooler like they all recommend.
That is, IN lINE. IN SERIES with your present tank cooler.
The tank first, then the new one, then back to the tranny.
The problem is that he can't. As he pointed out, he's replacing the radiator with an aftermarket unit that doesn't have an integrated cooler.
Install the aftermarket cooler like they all recommend.
That is, IN lINE. IN SERIES with your present tank cooler.
The tank first, then the new one, then back to the tranny.
The problem is that he can't. As he pointed out, he's replacing the radiator with an aftermarket unit that doesn't have an integrated cooler.
Steve - The reason I say electronic controls cause it to be more effected is that typically the computer will alter trans operation to try to warm it up faster. However, a hydraulic tranny will typically run fine (except for small changes in shift firmness, etc) until the fluid is so cold that the trans can't pump it and actuate the shifts properly.
I'm aware that the computer tells the hydraulics what to do, but its ability to compensate for cold fluid, etc. are limited. The trans definitely doesn't shift any later when cold than when warm (and neither do either of the Jeep 42REs I've dealt with), and I don't know of anything in the computer that should cause that. When it sticks when cold, it doesn't shift late, it just won't shift at all until I back off the throttle. When the fluid is too thick, it seems to need a greater difference in the hydraulic pressures for it to actually be able to shift.
I'm aware that the computer tells the hydraulics what to do, but its ability to compensate for cold fluid, etc. are limited. The trans definitely doesn't shift any later when cold than when warm (and neither do either of the Jeep 42REs I've dealt with), and I don't know of anything in the computer that should cause that. When it sticks when cold, it doesn't shift late, it just won't shift at all until I back off the throttle. When the fluid is too thick, it seems to need a greater difference in the hydraulic pressures for it to actually be able to shift.
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