Transmission Oil Hot light?!?

[FLowell]

On two occasions I have had this light come on when my transmission oil temperature gauge is indicating less than 150 degrees. It only happens when I am putting a load on the engine/transmission while backing up my fifth wheel on a small incline or towing my fifth wheel up my driveway, which is short, but steep. The two times it has happened, I probably haven't had the engine running for more than 10 or 15 minutes and the light goes out fairly quickly once I stop and let the engine idle in N. I might mention that I have a Mag-Hytec transmission pan with the oil temperature probe locateded in the hole they provide. How hot does the transmission oil have to get to bring on the Transmission Oil Hot light and where is the factory probe located?

 

[JimBob24]

I have a friend who has run into the same situation. His temp light comes on when he is doing slow speed maneuvering while parking his fifth wheel. You are in that slow speed high rpm situation with an unlocked torque converter which really can really produce some serious heat.



The transmission control module gets its temp readings from an electronic device called a thermistor, which is part of the governor pressure sensor located on the lower part of the transmission inside the oil pan. It is always immersed in ATF.



According to the manual, The trans temp light comes on at 260 deg. F. , which is a bit hard on the fluid. On the 48RE, if you are in 4th gear and this temp is reached you will get a downshift to 3rd and the torque converter clutch will lock. Unfortunately, in your situation you are in 1st and the TCC is going to remain unlocked, generating all that heat.



If you have 4WD and are maneuvering on gravel, grass etc. or even backing straight on pavement you might try 4WD low and see if that helps.

 

[jelag]

Transmission oil temperature should be tested in the pan..... transmission fluid over 200 *F. will start to decay and loose it properties fast..... I don't know the exact figures but something like over 230*F and its 50% of the life of 200* oil... oil over 250* has 25% of the life of oil at 200 and oil over 275* is ruined... .

I'm sure someone who knows oil can give the exact numbers... every one that I know of that pulls with a gauge has installed some method of adding extra cooling for their oil... . My BIL as an example added a 20K lb additional cooler with filter that holds 1 quart of oil... this has always kept his temp below 200* pulling the mountains of the pacific NW.....

Hope this helps...

 

[JValdez]

I think his question is about the gauges. His gauge is reading only 150 and the factory light is coming on, which means it's reading 260. Don't know??

 

[FLowell]

That's my question -- if my Autometer Transmission Temperature gauge is reading under 150 degrees and I'm getting a Transmission Oil Hot light, what's going on? Any ideas?? Fred

2005 3500 Quad 4x4 48RE

 

[2broke2smoke]

go buy a 40$ temp gun ... the little jewels that you point ... pull the trigger and it gives you temp





point it at the transmission pan ...



cheapest easiest way to see who's right ...



and you'll have a handy tool for future use

 

[ANG012]

Your transmission temp probe should be as close to the transmission in the line coming out of the transmission going to the cooler. In the pan all you get is the temp in the pan. Your transmission temp coming out of the transmission could be 260 and give you a over heat light.

 

[robertyoke]

check your fluid level.

if level is below the sending unit then it will not read correct. the mag hytec pan has the sending unit hole fairly high. the pickup is in the bottom of the pan so you can lose a lot of fluid and the trans will act normal. With less fluid it will heat the fluid faster and may be why the light is turning on.

I would start there. then I would look into a bad sending unit on the autometer. backing up a hill with load heats the fluid fast.

I like the sending unit in the cooling line then you can see what is going on before it is too late.

-robert