Transmission slow to warm up

[Yadkin]

I rebuilt my Cruise-O-Matic as part of this restoration and it works perfectly- except when cold. It just won't shift into 3rd for, I'd guess, five to ten minutes of driving. I'm assuming that the reason is higher viscosity of the fluid when cold.

I have O'Reilly's Type F in the system and the level is correct. Do I need to change to another brand of fluid? Or is there an additive that I should use to reduce cold viscosity?

[simplyconnected]

Are you using an 'automatic transmission' radiator, or do you have a separate transmission cooler?

[Yadkin]

I have a separate cooler mounted in front of the radiator, behind the AC condensor. I also have an electric cooling fan, behind the radiator with a tight shroud that doesn't turn on until the coolant is hot, then modulates the fan speed to keep the coolant at the set point.


The problem is most pronounced when I'm driving from my cabin in the mountains. It's a 3 mile coast downhill until I get anywhere, so the engine doesn't get to operating temperature either.

[simplyconnected]

I think you solved your own problem by identifying the cause...
OEM radiators integrate a tank in the bottom that serves two functions. In winter, your engine's thermostat quickly warms coolant until it reaches the proscribed temp, then it opens to convey heat to WARM transmission oil in the radiator.

Depending on ambient temp, the engine normally reaches thermostat temp within two miles. By separating the transmission cooler, you have eliminated any chance of warming by the cooling system.

The trans cooling design engineers really hit on a winner by integrating both heating and cooling functions in one radiator because:

• The bottom tank of the radiator is below the transmission's fill level,
• The trans cooling tank is out of the way of the A/C condenser,
• Fan placement is never an issue,
• Trans fluid cooling temp is REGULATED for consistent viscosity,
• The tank is protected from stones because there are no fragile and vulnerable cores filled with oil.

It makes sense that corporate wide, ALL brands of autos use the same radiator method to warm and cool automatic transmission oil. - Dave

[pbf777]

I doubt that a different brand of fluid or rerouting cooler lines would solve this problem (but I have been wrong before!), as the transmission should function properly even when cold (reasonable), with the inherently heavier viscosity fluid which accompanies such.

I certainly can't diagnose for certain exactly what's wrong from here, but, "as-a-wild-a**-guess", I'm thinking a control problem within the valve body, such as a miss-positioned and or binding/sicking shuttle/spool valve which "frees-up" with heat, expansion and vibration?

I wouldn't buy any lottery tickets with these comments, but you asked. Scott.

[Yadkin]

I suspected the separate cooler was the problem. Dave, is there any way to clean the heat exchanger that is part of the radiator? I don't want to hook it up only to run debris into my newly rebuilt transmission.

[simplyconnected]

Good transmission shops across the nation are equipped to flush your transmission lines and radiator tank. Call around your neighborhood trans shops and ask about their rates, how long it takes, if there is a warranty, etc.

[Joe Johnston]

Sorry guys, but I'm not buying the external cooler causing his tranny to not shift for 5 - 10 min. He lives in NC and it isn't below zero there. Those of us who have lived in colder climates may have experienced a bit longer than normal shift points on sub zero days, but even at that, its only minimal. A few seconds perhaps, but 5 min or more?? No way - even on the most bitter cold days driving with a cold engine. I am most certainly not a trans expert, but I highly suspect an internal problem like a sluggish or sticky valve body component.

That said, a fluid change and perhaps a flush may help as well as a product like Trans X. Won't hurt, worth a try and if no help, it can still be checked by a good trans shop.

[scumdog]

I'm with Joe.

So before going through all the rigmarole of hauling out your radiator and getting your trans cooler tube in it replaced/repaired etc how about trying this:

Cut out a piece of cardboard the same surface area as the front of the cooler and tape it over the front of your transmission cooler.

That would stop the airflow from doing any cooling so that way you will see if it is fact any relevance to your shifting issue.

Remember not to leave the cardboard there forever!!!!!, once the motor temperature is up to normal I would remove the cardboard to avoid the risk of overheating the trans fluid.

[Yadkin]

Sorry guys, but I'm not buying the external cooler causing his tranny to not shift for 5 - 10 min. He lives in NC and it isn't below zero there. Those of us who have lived in colder climates may have experienced a bit longer than normal shift points on sub zero days, but even at that, its only minimal. A few seconds perhaps, but 5 min or more?? No way - even on the most bitter cold days driving with a cold engine. I am most certainly not a trans expert, but I highly suspect an internal problem like a sluggish or sticky valve body component.

That said, a fluid change and perhaps a flush may help as well as a product like Trans X. Won't hurt, worth a try and if no help, it can still be checked by a good trans shop.

The transmission is was rebuilt last year and operates perfectly when warm. Not a lot of miles on the fluid that's in there. The long warmup times that I experienced happen when I start from cold at my mountain cabin down to Banner Elk, a drop of about 1200' in 4 miles. The engine doesn't even get up to operating temperature. Morning air temperatures are in the high 60's. A typical trip to Lowes hardware is about 5 miles and the transmission never shifts into 3rd. But, when I stop the engine and restart ten minutes later to make the trip back up the hill, third gear is immediately available.

Here in Clemmons where it's about 15 degrees warmer and a lot flatter, the engine/ transmission warm-up time is about half of that.

I have a 180 degree thermostat and an electric cooling fan that comes on at 190.

[pbf777]

You have acquired a fine observation that your transmission is sensitive to temperature for proper operation, but, your belief that the temperature is the problem which requires addressing seems faulty.

As stated by others, as the temperature falls the shifting function will be affected, but not to the "degree" as you depict; especially if only in the 60s' (F°). Scott.

[Yadkin]

I think you solved your own problem by identifying the cause...
OEM radiators integrate a tank in the bottom that serves two functions. In winter, your engine's thermostat quickly warms coolant until it reaches the proscribed temp, then it opens to convey heat to WARM transmission oil in the radiator.

I finally got around to removing my external cooler, cleaning out the radiator and using the OEM setup. The issue isn't gone but it is better. Test drove this morning, temperature around 60F.

Not sure if a name brand of fluid would be better, or trying some kind of viscosity improver would help.

[Yadkin]

The only thing that I find that remotely addresses the issue is Lucas Automatic Transmission Fluid Conditioner #10441.

http://lucasoil.com/pdf/TDS_ATF-Conditioner.pdf

"maintains cold temperature properties"
"improves shifting performance"

I've never had much faith in these type of products.

[pbf777]

I normally advise against using these "miracle in a bottle" elixirs, as anything but a last ditch possible solution prior to removal of the transmission for proper repair. One of their functions is to have an adverse effect on the soft sealing elements within the transmission. The intent is to cause worn and/or collapsed o-rings to swell in order to recover improved sealing performance. This may provide a fine but perhaps only temporary "fix" (popular with used car lots), later, often the effect causes hardening of these sealing elements and inevitable failure requiring a complete replacement. Scott.

[Yadkin]

There's literally a dozen bottles of stop leak and other junk like that on the shelf at O's, A's and others, including offerings by Lucas. I rebuilt my transmission recently so that is not the issue. The product I listed was not advertised for that.