Auto trans temps chart

[FrankR]

Automatic Transmission Fluid Oxidation
Automatic transmission fluid will provide 100,000 miles of service before oxidation occurs under normal operating temperatures of about 170°F. Above normal operating temperatures, the oxidation rate doubles (useful life of fluid is cut in half) with each 20° increase in temperature.

The approximate life expectancy at various temperatures is as follows:

175°F 100,000 miles
195°F 50,000 miles
212°F 25,000 miles
235°F 12,000 miles
255°F 6,250 miles
275°F 3,000 miles
295°F 1,500 miles
315°F 750 miles
335°F 325 miles
355°F 160 miles
375°F 80 miles
390°F 40 miles
415°F Less than 30 minutes

This information clearly shows why transmission oil coolers and the various maintenance intervals are recommended for severe usage.

Above 300°F, the metals inside the transmission will warp and distort in varying degrees depending on the severity of overheat. Because this damage occurs and fluid life is so seriously impaired, rocking out of snow, mud or sand should never exceed a very few minutes.

[ALANSD]

What do you think about transmission conditioners? At an auto dealership I used to work for they recommended adding this product...

[FrankR]

Please explain. I've spent the greatest part of my life in the mechanical world and have never heard of a trans conditioner. Is this like a filter cooler??? Frank

[ALANSD]

Sorry, what I meant was an additive...there is one particular brand that dealerships sell exclusively ( I can't remeber the name right now) , they make an oil treatment and a transmission conditioner treatment, supposedly makes the trans run cooler.

[FrankR]

In my opinion, there is no additive that allows for better cooling. There are anumber of additives that are supposed to make the old seals soft again. Cooling of a liquid is based mostly by the fluid characteristics as in viscosity. Viscosity is the ability of a fluid to flow under a variety of temps. Mostly it is hard to cool fluid too much. There are t-stats made for extreme temps also....... Frank

[PeterH-350LE]

Frank,
you earned the invisible title of mechanical guru of this forum with the trans temp post.
I would very appreciate your input in the motorhome forum>exhaust thread.
TIA

[ALANSD]

I second Peter's vote. I have been working on cars and trucks all my life ( my family owned a repair business) but Frank has definitely got the knowledge and ability to share it. Thanks for your input. Actually a big thanks to all who input here, Andy from Inland RV, and all the others who share the wealth of knowledge that we all need to tap into.

[PeterH-350LE]

Frank,
where on the transmission can you mount a temperature sending unit?

[FrankR]

Trans are just a great hydraulic pump of sorts. As with most mechanical devices heat can destroy any. There has been a great debate for a long time to install a temp sender. It is my opinion that the hot fluid line leaving the trans is the best place for a temperature sample. Several "hot rod" product companies make a inline fitting for a temp sender. I'm also NOT a big fan of integrated fluid cooling with engine cooling water, as in radiators with a coil for auto trans. I have found that a devorced fluid cooling system will better serve the trans. Synthetic auto trans fluid will absorb lots of heat with no failure of the unit. Most auto trans like temps about 175-185 F. but modern engines use a 192F thermostat. I've been using a 180 t-stat for about 2 years with no problems. The best trans cooler is mounted in such a fashion to receive ram air but also has a good fan to aid cooling up a long hard pull. Water spray cooling methods are not good. Many guys use plain tap water that is hard water and the coils or plates become coated the mineral deposits and the cooling is negatively effected. When pulling a long hard hill, shifting to a lower gear is a good way to reduce all temps. Factory gages are about 20% too high or too low. Stewart Warner is a great maker of quality gages. Frank

[Jim W]

I think that the new GM pickups & Suburbans come with a trans temp gauge included in the tow package. I have thought about putting a gauge on my 99 Suburban on my next trans service. GM must think they are worth while if they are starting to include them in the package.