Transmission temperature readings after pulling a hard climb.

[Barn Owl]

I took a trip up to Lake Moomaw last weekend and I pulled some very steep, long hills on the way. My short weekend trips are spent mostly here in the Appalachian Mountains and my bus sees many slow climbs in first gear not locked up. I try to keep the v730 in lockup as long as I can but when the hills are this steep it just drops out and I am left creeping up the grade. The transmission has an oil/coolant heat exchanger and fortunately, the PO increased the radiator size from the stock four core to a seven core. If my gauge is correct I have never had the coolant over 200 degrees. The engine coolant line from my heat exchanger (hot side) using an IR thermometer gets a reading of about 198 degrees. When I take a temperature reading from the oil outlet on the transmission after one of those hard pulls, I have seen readings of 240 degrees. I know those temperatures are way up there and that has led to some questions.

1. How close is the IR reading to the actual oil temperature? Would it be close to a transmission gauge? I am going to put a transmission gauge on the dash in the near future. I just want to know if I am in the ballpark when I read it from my gun.

2. Would putting an air cooler ahead of the other cooler help? I know many owners do it to help keep from dumping the extra heat into the cooling system but I am not having that problem (but I still don't like dumping a lot of heat into the engine). Another option would be to put it after and use a thermostat to control the fan. How would you all do it? I don't want to spend the money if I wouldn't get much of a return on the actual transmission oil cooling.

3. What temperature readings are you all getting?


I have the transmission oil tested once a year and so far, it has been ok. I know lower temperatures would benefit the oil and transmission by extending the service life. I just don't want to throw money at it.

Thanks,

Laryn

[JohnEd]

Laryn,

In a non Alison I read that they wanted 180 and anything over 200 degrees was shortening the life of the trans significantly.  Those use ATF.  They also aren't very efficient if they are too cold.  You seem to have proven that you have enuff rad.  You would get a lower trans temp if your aux cooler was after the rad.  The thermostat is a must if you want it to warm up in the winter.  I would prefer to have a thermostat controled by-pass valve for the winter and to hasten warm up but I am clueless as to where to get such a valve.  Anybody have that info?

John

[TomC]

Laryn- when the V730 is in second pulling a hill and you slow down enough to feel it come out of lock up, when that happens, pull the gear shift down into 1st with the gas pedal still on the floor.  When it shifts into 1st pull up about an inch on the gas pedal and the transmission should bump back into lock up.  Then you can still pull a long grade at around 30-35mph with it in lock up to avoid the high transmission temperatures.  It also works in reverse coming down a steep grade-just pull the gear shift to 1st and the trans will stay in lockup as low as about 15 mph-which works well if you also have a Jake brake.  Good Luck, TomC

[JackConrad]

Laryn,
    We added an aux. transmission cooler on our MC-8 740 Allison. Here is how we installed ours.  We found a Hayden cooler that just about completely fills the passenger side engine compartment door. The cooler line from the transmission (which is the fluid leaving the torque converter) goes to the top of the aux. cooler. From the bottom of the cooler the fluid goes to the OEM cooler on the engine and from the OEM cooler back to the transmission. The transmission temp senser  mounting position is right next to the hose from the transmission to the aux. cooler. (since this fluid has just left the torque converter, this is proabably the hottest the fluid gets). I installed the system this way assuming (yeah, I know what @$#- u-me means) that until the transmission is warmed up, having the fluid go through the OEM cooler will help shorten the warm up period. And after the transmission is warmed up, theoreticlly anyway, if the fluid is cooler than the water, it would actually remove heat from the engine. I don't think this actually happens.  we have found that since added the aux cooler all our temps (Transmission, oil, and water) run about 10-15 degrees cooler.  Jack

[Barn Owl]

Transmission temperatures are not on the hot list I see. Thanks for the response everyone, I am going to keep up the oil analysis and try to run a cycle to determine if it is worth adding an additional cooler to the system. If the change intervals are long and drawn out then I will just keep an eye on the temperature and oil oxidation and change it when needed.