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Old 05-27-2017, 02:46 AM   #1
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Safe Spec Boxster Tranny Temp

Searched around without much luck. Lots of talk about SBR tranny coolers but what is the proper temp range for the tranny oil. Looked at Redline specs they just tell you how the viscosity changes not where the oil starts to fail. Changed the tranny oil for the first time in a used SBR I bought and found that the tranny cooling pump doesn't work, so I am looking specing a proper cooling system. I have seen some general statements that manual tranny oil should be between 175 + 200, and anything over 240 breaks down the oil. 175 seems low.

Thanks for your help
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Old 05-28-2017, 12:41 PM   #2
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Originally Posted by Black Sweeper View Post
Searched around without much luck. Lots of talk about SBR tranny coolers but what is the proper temp range for the tranny oil. Looked at Redline specs they just tell you how the viscosity changes not where the oil starts to fail. Changed the tranny oil for the first time in a used SBR I bought and found that the tranny cooling pump doesn't work, so I am looking specing a proper cooling system. I have seen some general statements that manual tranny oil should be between 175 + 200, and anything over 240 breaks down the oil. 175 seems low.

Thanks for your help
Is this really a problem? Do people blow transmissions?
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Old 05-28-2017, 01:09 PM   #3
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Is this really a problem? Do people blow transmissions?
While not a maintenance item like tires and brakes, it is fairly common to have to replace a transmission. I know several racers who are on their 3rd or 4th transmission.

I will say that its hard to know if the failures are caused by high temps, too many miles, driver misuse, or something else. Personally, I am on transmission #2 and I blame the problems with trans #1 on myself (and some sloppy shifting).

Also, I see a few Spec Boxster's with external transmission coolers so there are some racers concerned enough about temps to try and do something about it. I do not run a trans oil cooler on my car but I do change the trans oil twice per year in the hopes that fresh fluid will provide some protection against heat. Still, I think that I (the driver) am my transmission's worst enemy.

In terms of trans oil performance, my limited understanding is that the trans oil is manufactured to a specification (like API GL-4 or GL-5) and then that spec has a defined test procedure (like ASTM D7450 or similar). I haven't done the research but you're likely to find the upper temp limit in those types of documents since all of the manufacturers just quote compliance with the spec's and rarely actually publish the numbers. With Porsche, it might even be more complicated since they might have their own spec which goes above the standard industry spec's (again, I don't know this for sure but its not unheard for Porsche to do something like that).
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Last edited by thstone; 05-28-2017 at 01:14 PM.
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Old 05-29-2017, 05:38 AM   #4
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Maybe it's a Texas thing but lots of guys run with transmission coolers down here and some even bring spare transmissions with them to the race. I agree with Tom and that most of the damage is caused by the driver.

Sorry Black Sweeper but I can't give you an answer but those temps sound about right to me and 175 doesn't sound too low to me.
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Old 06-04-2017, 07:04 AM   #5
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Researched Temps

Thanks for the comments. I did a lot more research and found that most tranny temp gages have 180 Degrees F as the center point and thermal switch options are 180 or 190 degrees. My tranny cooler has a driver operated On/Off switch but no temp gage to tell you what the temp is. So I am adding a 180 thermal switch to turn on the pump as well as an indicator light to show when the pump is on. Next step is to figure out how to interface a tranny temp sensor to my AIM Dash and try to get a temp read out there. Worse case add an Autometer Tranny temp gage. Thanks
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Old 06-04-2017, 09:16 AM   #6
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the problem w having a temp sensor to turn on your pump is no place to put it? most use the fill and drain openings on the transmission to circulate the oil, so no place for the sensor. you put the sensor on the cooling system and it doesn't see flow unless the pump is running - sort of a chicken and egg situation. unless the PO drilled the transmission for a sensor or the oil return?
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Old 06-04-2017, 10:46 AM   #7
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the problem w having a temp sensor to turn on your pump is no place to put it? most use the fill and drain openings on the transmission to circulate the oil, so no place for the sensor. you put the sensor on the cooling system and it doesn't see flow unless the pump is running - sort of a chicken and egg situation. unless the PO drilled the transmission for a sensor or the oil return?
A couple of the cars that come into the shop have mounted a gear oil cooler using the drain plug as the pickup and the fill plug as the return; they also have a temp senor in the line going to the pump.
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Old 06-04-2017, 04:49 PM   #8
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A couple of the cars that come into the shop have mounted a gear oil cooler using the drain plug as the pickup and the fill plug as the return; they also have a temp senor in the line going to the pump.
great place for accurate oil temp when the pump is running, but you couldn't use the sender to turn the pump on or off, or even decide if the pump needs to be on, because when the pump isn't running the reading wouldn't be very accurate.
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Old 06-04-2017, 05:16 PM   #9
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great place for accurate oil temp when the pump is running, but you couldn't use the sender to turn the pump on or off, or even decide if the pump needs to be on, because when the pump isn't running the reading wouldn't be very accurate.
I think what they do is run the pump continuously when at the track, and maybe in heavy traffic on the street. You will need a separate bung welded into the gear box case to have the lube trigger the pump.
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Old 06-05-2017, 04:02 AM   #10
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I have also seen small surface mounted temp sensor attache to the trans case to trigger the pump.
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Old 06-06-2017, 08:48 PM   #11
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Not a Boxster-specific answer but most gear oil is designed to operate best between 160-220F. Below 160 things can get a little stiff and above 220 you lose viscosity and risk damage to seals and bearings.

That said I agree with Tom that 90% of trans breakdowns are driver related. I tossed the pinion bearing in mine with torque spikes while getting airborne on the whoops running the historic track at Pomona. Fun but expensive.
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