Over-cooling the Transmission?

[LeSabre in Buffalo]

Is over-cooling a transmission possible?

I'm asking because after installing a transmission cooler (see other threads here and here), my transmission doesn't seem to get above 160* F on the highway in some pretty hot weather. It varies a bit, but always goes back down to 160 when the car is moving. Also takes forever, as in 20 minutes, to reach this temperature. Many of my trips are far less than 20 minutes. Should I be concerned my transmission isn't getting up to 165-170?

[JMH1950]

As long as it's getting warm enough to go into TCC lockup I wouldn't worry about it.

[wjcollier07]

I don't think 160 is a bad temperature for it. That's not THAT cold. The fluid will oxidize much slower, and much lower heat will keep varnish and other crap from building up as quickly.

But I believe that B&M is a thermostatically controlled bypass with plates that allow thinner, hot fluid to enter the whole cooler, and thicker, cooler fluid to bypass most of the cooler.

I don't think you have much to worry about. But that's a *dang* good cooler you have there.

[LeSabre in Buffalo]

Yes, it's the viscosity-controlled B&M. And yes, the TC locks up with no problems.

It's a good cooler. I'm wondering if it may be too good!

[willwren]

I have the 28000gvwr B&M thermostatically (viscosity) controlled cooler on the Zilla. Even in Oregon winters (harsher than yours), I have no problems with TCC lockup after about 5-10 minutes of driving. If you do, cover half the cooler in the winter with a piece of cardboard.

[LeSabre in Buffalo]

Fantastic! That's a worry off my mind.

The winters down here in South Carolina won't be anywhere near as harsh as in Buffalo. That's right, the LeSabre's left Buffalo! It's not the cool down here, it's heat on acres of asphalt.

[BillBoost37]

For the 4T65 to be up to operating temp is considered being at 160F.

In the case of being in CT, the trans wouldn't get over 113F in the winter with a cooler on it. Removed the cooler and it's better. Summer temps are usually in the 160-175 range with the occasional hot day temps of close to 190-195F on the stock cooler in the radiator.

Most of the time the fluid leaves my trans to be heated.

[Jrs3800]

A trans does not want to be bone chilled cold... Thats why I recommend a Thermostatically controlled cooler for those in the cooler climates..

Down here this is not an issue as a trans will easily see 200F-230F... I like to see the trans run 160-180F with a cooler..

[LeSabre in Buffalo]

To update:

Yes, this cooler IS entirely capable of over-cooling the transmission. Temperatures driving from SC to NY ranged from 160 on the highway in mid-90's temperatures down to 120's at the mid-60's night. When the transmission got down into the 120's, the car felt sluggish and my fuel economy plummeted. So much for viscosity-controlled! I also think I was defeating the control with how the cooler was installed directly in the airstream flowing over the lower portion of the radiator.

I redid the setup, moving the cooler out of the airstream and into the slower-moving air behind the bumper and grille. This appears to let the cooler function as intended, not shedding all the heat it's capable of shedding. Results of a test drive flogging the car up a fairly long, steep hill and coasting down the other side suggest that once 160 is reached, it will stay there with minimal variation.

See my cooler installation thread for pictures on the redone setup.

[LeSabre in Buffalo]

Update again:

Moving the cooler has solved the problem of not enough heat on the highway. But the around-town temperatures weren't so hot. So the lines got shielded better, moving the around-town temperatures into the 130-140* range after 10-15 minutes of easy driving.

To those of you who have external coolers, what have your experience been?

[agrazela]

Are you still running your ATF through the radiator's built in "cooler" first, and still over-cooling? If so, then I guess it's fair to say your cooler's too big. At least for Fall/Winter.

Do like wren suggested and cover part of it with cardboard in colder months.

(BTW, mine's rigged exactly like yours; but it's much, much smaller)

[2000Silverbullet]

I have used a trani cooler since the car was almost new.
The ideal temperature for hydraulics is 130 F
I don't like to push much power thru the trani until it is at least up to 110 F
For every 10 F the trani operates higher than 160 F, the life of the trani will halve. An old addage but very true when it comes to seal life.

Mine will run at 160 F but as others have said, it is being heated by the cooler inside the engine coolant radiator.
Mine is placed directly in the airstream.

The more surface area for shedding the heat produced by the inefficiencies of this engine, the better!

[BonneMe]

I have used a trani cooler since the car was almost new.
The ideal temperature for hydraulics is 130 F
I don't like to push much power thru the trani until it is at least up to 110 F
For every 10 F the trani operates higher than 160 F, the life of the trani will halve. An old addage but very true when it comes to seal life.

Mine will run at 160 F but as others have said, it is being heated by the cooler inside the engine coolant radiator.
Mine is placed directly in the airstream.

The more surface area for shedding the heat produced by the inefficiencies of this engine, the better!

Standard Hydraulic systems in machinery are different than a conventional std automatic transmission. Fluids are made to be used under different uses, temperatures, pressures, etc.

Transmission temp is only one of many variables in trans life. My '93 was over 150k on the original slushbox, and it had seen more than it's share of assorted abuse, the engine never got a lower stat, the trans never got an aux cooler, neither ever had a problem.

[BillBoost37]

Overcooling is possible. Intense suggested to me that I not abuse the trans until operating temp of about 160F was achieved.

Too cold is too cold and it sounds like you may have too large of a cooler or a bypassed radiator cooler/preheater. A 4T65 runs a lot cooler than it's hot headed 4T60 predecessor. The 65 was based off things they learned from the 60 that it would run too hot and changes were made. The 65 was also designed to back up an engine with more power and more torque, which typically would cause more heat in the trans.

[2000Silverbullet]

Standard Hydraulic systems in machinery are different than a conventional std automatic transmission. Fluids are made to be used under different uses, temperatures, pressures, etc.

No it's not any different than other hydraulic machinery. In fact, it uses the same fluid!

160 F is hot enough for hyd oil to operate efficiently.

130 F is hot enough also, and believe it or not, is ideal. You don't have to wait until the fluid is hotter than that.

Of course there are many variables that other than temp that affect trani life but by far, temp is the greatest determining factor.

[BillBoost37]

This is only my opinion and not trying to start anything here, but I'm more apt to listen to experts that rebuild and race their transmissions vs someone who works on mill machines when it comes to cooling and it's effects on a transmission of a car.

Any facts about the 130F fluid temps or manufacturer TSB's etc showing that 130F is better than 160F?

My personal experience is similar to the OP's, mileage, shifting etc is better when the trans reaches it's manufacturer specidifed operating temperature of 160F.

[LeSabre in Buffalo]

Are you still running your ATF through the radiator's built in "cooler" first, and still over-cooling? If so, then I guess it's fair to say your cooler's too big. At least for Fall/Winter.

Do like wren suggested and cover part of it with cardboard in colder months.

(BTW, mine's rigged exactly like yours; but it's much, much smaller)

Yes. It's routed transmission->radiator cooler->external cooler->transmission.

I've already shielded the lines, which has made a giant difference in how the transmission heats up. Next I will try duct-taping a piece of cardboard over the lower half to see what effects it has. Will have better results this weekend after doing a road trip.

[2000Silverbullet]

This is only my opinion and not trying to start anything here, but I'm more apt to listen to experts that rebuild and race their transmissions vs someone who works on mill machines when it comes to cooling and it's effects on a transmission of a car.

Any facts about the 130F fluid temps or manufacturer TSB's etc showing that 130F is better than 160F?

My personal experience is similar to the OP's, mileage, shifting etc is better when the trans reaches it's manufacturer specidifed operating temperature of 160F.

No you never TRY to start anything.......you just do!

I am more apt to believe an industrial Engineer who has experience over 35 years in industry installing new and rebuilding existing hydraulic equipment working with mega hydraulic experts who supply this equipment. Have also been involved with many failure analyses and their causes. Too bad Google has no access to those.

No disrespect to Intense but their experience is very limited and I think they use 160 F loosely. Most of the time on normal 30 minute trips, the majority of the trani's time is spent at temps a lot lower than 160 and it operates just fine.

You have to worry about over cooling if it is taking too long for the temp to get over 110 F.
I have used the cardboard trick in sub zero temps, but for me that is rare.