Tranmission Temps - What is too high?

[Rob T]

Hi: On a whim yesterday after about a 20 minute session on the track, I took the infrared temp gun and shot the transmission. I was amazed that the top rear of the transmission was 210 - 220 and the top of the transmission above the axles was 250F. This was my third session of about 25 minutes driving with about 35 minutes off. I have a 5MT from a Legacy GT with a Modena TBD LSD. I talked to Paul at Yimisport (they build monster Subaru Time Attack cars) and he said 250 was the max. He also said this is a splash lubricated transmission, so adding a cooler would be a bit of a project with plumbing, a cooler and a pump. He recommended changing the fluid every two to three track days and likes Motul 300.

Has anybody had any experience with the transmission temperature issue, or is this a non-issue? I've never looked. What are the other track cars doing about their transmissions? Has anybody looked at the temperature?

[DodgyTim]

Eaton list 250°F(121°C) as the maximum temperature but also mention that is the bulk oil temperature, and that at 250F (bulk oil temperature) the actual loaded gear teeth temperatures may exceed 350°F(177°C), which will ultimately lead to premature gear failure

[DanielsDM]

The Dragonfly Racing 818 had a gearbox failure in the Portland Enduro last October, after about 4 hours. I plan on putting a temp sensor in the box, though I haven't figured out where yet (still have rest of the car to finish).

[RetroRacing]

We use a cooler and a gear type oil pump, so we have not seen these kind of temps after 30 min running. We pick up from the drain plug and return into the filler tube, so there is no effect on the workings of the transmission. We are also running another liter of oil, due to the volume of the cooler, lines and such. I am installing a temp sensor into the feed line to the cooler for information sake, but don't like a temp switch, just one more think to fail. We were running motul, but have moved to the Amsoil GL-4.
Dragonfly was not running a cooler, but they are now.

[DanielsDM]

What pump are you running?

[Mitch Wright]

Rob,

If concerned I would suggest getting the actual trans oil temp I have never felt comfortable taking a infrared reading like that especially in just one location. Trans oil temp will tell more of a story IMO. Does your oil smelled or look burnt?

[Rob T]

Retro: I was thinking about a cooler as well. Can you give some of the specifics of the components you used? That would save a bunch of design time I was thinking about it the same way you did.

[RetroRacing]

We use a gear oil scavenge pump (do and ebay search, but they here is a link) https://www.ebay.com/itm/NEW-Heavy-D...-/231357370990
Drill and tap a hole in the drain plug for a 1/4" npt fitting, dash 6, to a 13 or 19 row oil cooler, then through an inline screen filter, then to the pump "in", then to a welded steel dash 6 fitting on the end of the fill for the transmission. To fill the transmission, you need to make a funnel with a dash 6 hose and female fitting on the end, so that you can unhook the "in" on the pump, and suck the oil into the transmission.

[Canadian818]

We use a gear oil scavenge pump (do and ebay search, but they here is a link) https://www.ebay.com/itm/NEW-Heavy-D...-/231357370990
Drill and tap a hole in the drain plug for a 1/4" npt fitting, dash 6, to a 13 or 19 row oil cooler, then through an inline screen filter, then to the pump "in", then to a welded steel dash 6 fitting on the end of the fill for the transmission. To fill the transmission, you need to make a funnel with a dash 6 hose and female fitting on the end, so that you can unhook the "in" on the pump, and suck the oil into the transmission.

Do you have pics of your setup? I recall seeing them once upon a time, but I couldn’t find your build thread.

[Sgt.Gator]

RobT, my LGT Grand-Am Cup race wagon I bought from the factory supported Subaru Road Race Team (Phoenix Performance, Joe Aquilante) had/has a tranny cooler with sensor. (Legacy 5MT). As Reto said, you tap a port into the drain plug, but in the Legacy tranny which you have, you can do the return to the tranny to the unused speedometer port. I'm not sure if this will work on WRX 5 speeds, there may be internal speedo drive stuff that prevents it.
The tranny temp sensor was in the AN line from the tranny to the pump. It never got over 190 as long as the pump was on. 250 is most definitely too hot. I'll bet when you drain it your tranny oil will stink!

The SRRT actually welded a steel -8AN fitting into the drain plug. Then ran -8AN lines to the cooler and the pump. The pump manufacturers want you to run the line to the cooler first, then the pump, to prolong pump life. The SRRT had theirs plumbed to the pump first, then the cooler, back to the tranny.

I think the LGT had a MOCAL pump. https://www.racerpartswholesale.com/...BoCC5YQAvD_BwE

5 Speed Drain Fitting.jpg..5 Speed Speedo Cooler Return Port cropped.jpg

And FWIW, in my STI 6MT I use the internal pump to send oil to a cooler. I just replaced the OEM exterior hard line from the front to the back of the tranny with 6AN lines looping to a cooler.