Can auto trans fluid be TOO cold?

[novadude]

I have an aux cooler in series with OEM cooler in rad. When driving down a level highway in OD w/ the converter locked in 20 deg weather, is it possible that the transmission fluid could be overcooled?

Been running it this way with no problems... I am just curious what the "experts" say.

 

[1maniac]

I am farm from an expert when it comes to ATF but I have the same setup you have. My ATF hits the radiator first then flows to the aftermarket cooler and then back into the transmission. I figure the coolant/antifreeze warms up the fluid and the cooler makes sure it doesn't get too hot. When I had my transmission rebuilt the rebuilder reccommended an external cooler and synthetic ATF.

 

[MolaKule]

Being that most ATF fluids are 5W20 (Dinos) or 0w20's (synthetics) and they have a high Viscosity Index, I would say that until the fluid warms up, the only issue is burning extra fuel to overcome viscous friction within the transmission. Also, colder fluids cause harder shifting. So as with engines, easy does it until the fluids warm up. One should drive slowly until the fluid heats to near operational temperatures.


If the fluid flows first to the radiator, and then to an eternal cooler with a temp valve, then the fluid temp should moderate.

Extreme heat is the number one killer of transmissions since heat oxidizes the fluid and causes varnishing of valves and friction surfaces; high fluid temps reduce the lubricating film thickness as well.

[ December 09, 2003, 06:05 PM: Message edited by: MolaKule ]

 

[medic]

My transmission won't let the torque converter lock up until the fluid is up to temp. I have a factory cooler, but I'm unsure what way the fluid flows.

Either way, I'm about 4 miles down the road before the torque converter will lock up when it is 20F or below. Idle time before hitting the road doesn't seem to matter.

 

[unDummy]

I can drive 5 or so miles on the highway before the transmission locks up. Transmission fluid can be too cold. If you're worried about an aftermarket cooler, get a fluid thermostat and temp gauge.
If the atf cools to the point that the previously locking converter unlocks, I'd consider blocking the airflow to the cooler(if OEM is still hooked up).

The radiator isn't always capable of heating up the ATF.

Unhooking the cooler is the easiest way to figure out which way the fluid flows. Wear goggles.

 

[MolaKule]

quote:

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Unhooking the cooler is the easiest way to figure out which way the fluid flows. Wear goggles.

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Or as my son says, be ready to spread a gallon of Goop all over your body and rinse well!

 

[novadude]

My AODE also will not let the converter lock until the temp is above a certain level.

I am using a factory Ford auxillary cooler plumbed in series after the factory in-radiator cooler. Fluid is Mercon V. As I suspected, it sounds like I have nothing to worry about.

 

[Kestas]

Isn't it better to run it through the aux cooler first, then the radiator? I remember this being discussed somewhere before (Allpar?). This would allow for good cooling of the fluid, yet warm it up with radiator fluid if it was too cold. The idea is to have a constant ideal warm temperature to the fluid - not maximum cooling.

 

[TooManyWheels]

Every recommendation I have ever seen from either a cooler or automobile maker says to run the fluid through the cooler first, so that the radiator can rewarm it in cool situations. I recently installed a factory General Motors retrofit cooler on my pickup and they also showed it plumbed this way.

On the other hand, the transmission rebuilders seem to prefer them to be plumbed with the cooler after the radiator.

My personal opinion is that, like the general state of oil related knowlege, the "street" knowlege is way behind the factory and engineering knowlege, so I vote for putting the cooler before the radiator.

 

[MolaKule]

Installing the cooler "after" the radiator is the preferred method for two reasons.

Installing the cooler before the radiator causes engine heat to flow to the transmission's oil before returning to the transmission, not good for hot weather. Installing the cooler after the radiator, causes the heat from the ATF fluid to flow to the radiator first, which has a larger cooling capacity than the external cooler, and then further cooling is accomplished by the external "after" cooler.

In cold weather, the engine coolant will warm up, thus warming the ATF first in the process. After warmup, the external cooler then further reduces the ATF temperature below that of the engine's coolant.

 

[VaderSS]

The factory installed oil/air transmission cooler on my car and all of the other cars I've seen, is downstream of the oil/water cooler. The recommedations I've seen in the install directions of the coolers I've purchased suggest the same.

quote:

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Q. Should the cooler be installed before or after the radiator?
A. Hayden recommends installing the auxiliary cooler after the radiator to return the coolest fluid directly to the transmission. Installing the cooler before the radiator will still provide additional cooling and may be necessary in some difficult access applications.

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[Alex D]

On three consecutive car now I have installed the largest stacked plate ATF cooler I could find, the B&M 28,000 GVWR race cooler, by completely bypassing the radiator cooler.
You may ask why. Well, I started thinking about this to relieve the engine cooling system from additional heat load in the summer, but I was also concerned about over-cooling the ATF. So I called a few companies who know about automatics. I did get feed back from B&M, Yank, TCi and Precision Industries (Vigilante, Stallion). All of these companies recommended this set up IF the cooler has a rating of 24,000 GVWR or larger. They recommended not to do this as long as the vehicle is within factory warranty because a set-up such as this, even though better, would void the factory warranty. In regards to the over cooling they commented that it would only take place in sustained sub zero temps and we don't have those here.

I have now had three cars with this set up and driven over 150,000 k miles with these set ups and they work great. ATF coolant does not exceed 200F even in the hottest summers and sustained city driving, mostly right around 180F. In the winter the oil warms up adequately within the first 10 minutes of driving. Removing the additional heat load of the ATF from the negine cooling system also has a very nice effect by keeping the engine temps significantly lower than before. Further a LPD (low pressure drop) ATF cooler has significantly less flow restriction than many or most of the in-radiator heat exchanges used to cool the ATF in an OEM set-up.

[ December 18, 2003, 10:16 PM: Message edited by: Alex D ]

 

[Rat407]

One question, has anyone ever heard of a major problem/damage with a transmission due to the fluid being to cold?

My guess it heat is the main concern, not the cold. But then this is a new topic for me. Doesn't get very cold here in NC.

At least not on the East coast side.

 

[Judd]

Hmmm, I've been wondering if the ATF fluid can be too cool also. I have converted my original AC condensor into a transmission cooler on my 83 Blazer.

When I first started thinking about doing it, I was going to run from the transmission to the AC condensor, to the original radiator cooler, then back to the transmission. I figured that the AC condensor would cool it down good, then the original cooler would bring it back up to temp.. Well, once I started plumbing everthing,, it was just plain easier to plumb it as follows. Transmission to original radiator cooler, then to the AC condensor cooler, then finally back to the transmission.

I have rigged up a mechanical water temp. gage in the transmission. pan and the pan temps are real cool. I purposely stalled-out the convertor for several minutes when I first got everything up-and-running because it took so long for the fluid to get above 100 degrees. After being stalled-out for awhile, it finally got up to around 150-160 degrees. Normal running, it never gets above 130 degrees.

At first, this really bugged me as I was worried that the fluid was not getting hot enough to burn off water condensation. But,, I got to thinking about some other things. First, the oil comeing from the transmission is hot for sure {especially when I was stalling-out the convertor}.

I wanted to install the temp. sender in the outgoing transmission line but the jerry rigg thing I had to use just didn't look right, it was a cast iron T fitting with brass reducers,, heavy as heck. Gave up on the line idea and just welded a bung in the transmission pan. Anyway, I'm sure that the oil coming from the transmission is plenty hot enough to burn off water. I live in Ga. BTW, so I don't see ambient temps much below 15 or so degrees. If I lived in Michigan, I might have to change my set-up.

I figure that when I'm out wheelin the Blazer, temps immediatly out of the transmission could be in the 200 degree range with my cooler set-up. I figure this because when I did my torture test {stalling out the convertor for a few minutes}, the line from the transmission was so hot that you could not touch it. It was still very uncomfortable to the touch once it came out of the radiator cooler. Once it came out of the AC condensor,,, the line was cool to the touch.

Sorry for the book but I have been doing a bunch of work on my Blazer recently in the cooling dept. {transmission cooler and a power steering cooler} and would like to get as many opinions as possible.

[ December 27, 2003, 06:51 AM: Message edited by: Judd ]

 

[TheTanSedan]

There are plenty of opinions on this subject, some of the more interesting ones on the diesel pickup boards, and RV boards.

I believe in doing it as the factory did: radiator internal cooler, auxiliary external cooler. (And external, auxiliary filter).

Recommendations on op-temp vary, (as do gauge temp sender locations). B&M Racing recommends a sump gauge (with which I agree, this is what the transmission "sees"); and in temps being at least 150F past warm-up. (As does the manual for my Aisin-Warner JEEP Cherokee transmission).

Cooler temps may be "okay", but moisture condensation has got to be gotten rid of. In the above set-up -- with the engine running a 195F or 205F thermostat -- one can be assured that the transmission fluid is being warmed almost as fast as the coolant. (One reason I believe that Chevy Corvettes used to, or still do, run an engine oil/water cooler: get op temps fast, and relieve temp spikes).

A stack plate cooler -- like the B&M pieces -- will bypass cold oil until heat thins it out to flow fully through cooler.

I have yet to see an oem trans fail to go 150k with regular service and the above.

 

[Ken2]

Keep in mind that the transmission cooler is inside the lower tank of the radiator. The thermostat temperature is reading the coolant in the head and modulating to send part of the coolant to the radiator for cooling and part back through the engine to maintain a constant temperature. That lower tank on the radiator can be very cold in frigid winter weather, and even on the hottest day with the thermostat fully open is cooler than the cylinder head coolant temperature you read on your temperature gauge on the dashboard.


Ken

[ December 30, 2003, 08:36 PM: Message edited by: Ken2 ]

 

[GT Mike]

My Grand Prix ('97 GT 3800 V6 4T60E transmission) will pull timing on a 1-2 gearshift if the ATF is not above 160°F It shows up as KR (knock retard) on the scan readings.

 

[heyjay]

I live in a climate where it can dip to -42 F in winter. I have seen -46 F once in my life.

It would be smart to run a winter front (In front of the grille, do NOT block the rad off) in temps colder than 0 F.

I put a 26,000 GVWR on my 1984 Ford F-150 with C6. If I didn't use a winter front it would shift VERY sluggish.

I'm going to quote from the Esso Lubricant Products Handbook, which is what I use as my "lubricant bible."

Quote: If the ATF viscosity exceeds 100 Poise, operation of automatic transmissions and fluid couplings will be sluggish or fail.

FWIW: a regular DexIII ATF hits 100 Poise at about -35 F. At -40 F, Mobil 1 ATF is 51 Poise.

Heavy Duty automatics, such as the Allison 4 speed, 5 speed, and 6 speed's, caution to do a "preheat" in temps colder than 20 F for about 20 minutes. That means the motor running so the ATF can warm up.

I have heard of auto's failing to shift in cold temps.