can you run an auto tranny too cold?

hayjayhorses · #1 Fri, December 18th, 2009, 10:45 PM

I am woundering if I am running my tranny to cold. F550 4R100 7.3. I have 2 tranny temp gauges one in the line going to the cooler, about 10" from the tranny. The other in the pressure port.

In this cold weather 0-30 degress the temp on the tranny line will not go over 100 unless i am in stop and go traffic with a good load on (no locking of TCC) the port temp getts to about 135, I think a lot of the pressure port temp comes from the engine via the aluminum tranny case.

I travel from Massachusetts to New York a few times a week (500-600 miles round trip) The last few trips with the ECT temp @ 170 to 180 (thanks to a peice cardboard covering the grill) the line temp stays below 100 and the case temp less then 135

When i pull a hill loaded the line temp will get to 140ish and then right back to under 100 on the flat

I put the largest tranny cooler I could find tru-cool LPD4739 in front of the ac condenser, witch is not getting direct wind (custom cardboard grill cover).

Han I harm the tranny by running it too cold? ATF getting to thick?? I am using mercon 5 tranny fluid. I am going to put amsoil ATF in it in a few weeks.

ChuckD · #2 Sat, December 19th, 2009, 03:04 AM

You want to try and keep your tranny to 160 IMHO.

hayjayhorses · #3 Sat, December 19th, 2009, 07:48 AM

sorry for my ignorance what is "IMHO"

thanks

***Power Hungry*** · #4 Sat, December 19th, 2009, 08:59 AM

IMHO = In My Honest Opinion

The transmission is designed to operate most efficiently at 160-200 degrees. Below this, the fluid viscosity changes and may affect the life of the transmission, although I couldn't say for certain. I do know that as far as the PCM is concerned, anything below 100-120 degrees is still considered "cold" and the shifting strategies change slightly.

If the fluid isn't staying up, I'd almost consider bypassing the additional cooler for the time being until the ambients warm up.

Your best bet? Ask a tranny professional what is too cold. Brian's Truck Shop, Suncoast, or any of a number of other professionals would be able to better advise you on this.

Take care.