Transmission Temps - How hot is too hot

[JohnJL]

I am seeing 240 F degrees on my transmission temp gauge at the track. I dont know if it will go higher still (the gauge goes to 260F) but that's what I can see on the camera looking at the end of my sessions at the short Cayuga track. I havent been to Mosport in a bit but I will soon and I wonder if it will get even hotter there. I dont recall what fluid I have in there, it was something Guard recommended. Its a G50 with a Guart LSD.

I havent checked the condition of the fluid, and I will. I also havent noticed any issues with the function of the LSD or shifting quality. However, I am putting together my winter project list and am wondering whether I need to plumb in an transmission cooler and pump. I'm not enthused about the extra weight, complexity cost or time involved but neither am I interested in losing the transmission or LSD because I cooked the fluid.

Opinions? For those of you tracking/racing your cars how many of you have transmission coolers? I have noticed lots of other makes with coolers at the track but many of them have very small diff volumes (ie MX5, RX7) necessitating them.

[JeremyD]

Gear Oil Max Temperature

(on my car (with a 3.6) I decided it would be much cheaper to plumb a cooler than do a transmission rebuild - I think that would be even more the case with a g-50. (I've never seen over 180 degrees with the cooler)

[JohnJL]

Thanks Jeremy.

David at Redline provided this response overnight:

John,

Thank you for contacting Red Line Oil, in your G50 transaxle the 75W90NS would be recommended. A temperature of 240° is not excessive, ideally you would like the fluid temperature to remain below about 295 to 300°. As the temperature approaches 300° the seals will start to loose integrity, then as temperatures reach 325 to 350° surface hardening on components can start to soften. For good component longevity the ideal maximum temperature should remain below 300°F. The gear oil provides extremely good thermal stability, will tolerate substantially higher temperatures than components.

Regards, Dave
Red Line Oil



From: John Landry [mailto:jlandry@xxxxx.com]
Sent: Monday, September 17, 2012 4:15 PM
To: info@redlineoil.com
Subject: Transmission fluid maximum temps

I am using your transmission fluid/oil in my 911 race car, the transmission is a G50 with a Guard LSD. I have a transmission temp gauge and am seeing 240 F at the end of the sessions. Is this OK? What are the maximum acceptable temps for your transmission and gear oils?

Thanks
JOhn

[spuggy]

According to Jim Patrick, G50 brass syncho's (if you didn't switch them out for steel) are sensitive to getting too hot. Apparently, there won't be any doubt when they're too hot, you'll be able to tell because the box will shift really badly....

So, if you're using brass synchros and the shifting is fine, they can get hotter than that


I chose to get the cases machined/plumbed for a spray kit/cooler fittings so this could just be bolted on later without dropping out of the car - if it proved necessary. I seriously doubt that it will in my application, but I'd rather have spent an unnecessary $200 or so against a drop, gearbox dismantle/machine/re-assemble and re-fit...

[JohnJL]

Patrick built my case too. I'm surprised that there would be a difference in brass vs steel in this case though, since we're talking about a difference of ~40F around 190F, where both of these metals' softening points are around 1700F and 1900F for brass and steel respectively.

[Matt Monson]

Originally Posted by JohnJL

From: John Landry [mailto:jlandry@xxxxx.com]
Sent: Monday, September 17, 2012 4:15 PM
To: info@redlineoil.com
Subject: Transmission fluid maximum temps

I am using your transmission fluid/oil in my 911 race car, the transmission is a G50 with a Guard LSD. I have a transmission temp gauge and am seeing 240 F at the end of the sessions. Is this OK? What are the maximum acceptable temps for your transmission and gear oils?

Thanks
JOhn

Originally Posted by JohnJL

I dont recall what fluid I have in there, it was something Guard recommended.

I NEVER recommend Redline gear oils for a synchro box, ever. There are 10 other oils I would put in before I would put Redline in a G50. I rarely recommend specific oils, but I don't ever recommend Redline.

240F is fine. I wouldn't be concerned about it until 275F+.

Regarding the brass versus steel, it has nothing to do with softening points. It has to do with coefficient of friction. Synchros need friction to function. As the oil gets hotter it becomes more slippery. Steel synchros have more bite than brass synchros. This is why the 996 GT3 Cups used them, and why now all street GT3s get them on 3-6 from the factory. When the oil gets hot and more slippery the steel ones keep biting. The brass ones, not so much.

Regards,

Matt Monson
Guard Transmission LLC

[spuggy]

Originally Posted by JohnJL

Patrick built my case too. I'm surprised that there would be a difference in brass vs steel in this case though, since we're talking about a difference of ~40F around 190F, where both of these metals' softening points are around 1700F and 1900F for brass and steel respectively.

Brass and steel are obviously different materials, but the relevant property in this specific comparison is the rate of expansion, rather than the softening point/hardness etc. It was explained to me as the brass expanding significantly more for the same temperature increase when compared to steel - and there's apparently a range of temps at which the brass just don't work as syncros anymore (until they've cooled down/shrunk), but the steel would be not have expanded as much and would still be fine.

[JohnJL]

Thanks guys. Every day is a school day!

[onboost]

Originally Posted by JohnJL

Thanks guys. Every day is a school day!

Well said! Excellent info!

[dshepp806]

Of course, I've no normal course to look into my tranny temps (on a stock 89/G50),..that is, I've no way of measuring, at present.

I WILL say that the Mobile One Delvac gets changed annually.

Drain plug is always clean as a new one!!!!!!!

BEST!

Doyle

[porterdog]

Originally Posted by Matt Monson

There are 10 other oils I would put in before I would put Redline in a G50.

Can we know the top 5?

[Matt Monson]

Originally Posted by porterdog

Can we know the top 5?

I don't pick favorites. The reason for this is two-fold. One is that when I do I get quoted and people take what I say as gospel because of what I do for a living. There are a LOT of good gear oils out there.

Two is because there is not a one size fits all, and that gets stacked on top of number one. Someone somewhere seeings me talking about Delvac and assumes that it would be just as good in their 901 as is it in their GT3 gearbox. Specific brands and formulations work bettter for different gearboxes and applications.

In fact, even my statement above was an overstatement. I said I never recommend Redline gearoils for synchro boxes. What I should have said is that I never recommend Redline oils for synchro boxes that are tracked regularly or raced. I know some really top teams that swear by Redline on their sequential Cup Cars. I also know some people with street driven G50 based gearboxes who live in northern climates and drive their cars year round and they swear by how smooth Redline is on a cold winter morning. What I said should not be taken as an indictment of Redline products in general or their gear oil line of product specifically. Though I will go on the record as saying that I think their Shockproof line of oils is junk. Their MT and NS are decent oils, in the right application.

So, in no particular order and with no reference to exact oil or vehicle or usage, the oils I would put into my personal vehicles are as follows:

Mobil
Swepco
Lubrication Engineers
Brad Penn
Castrol
Motul

That's 5 right?

[JohnJL]

Thanks Matt.

Would you be willing to give a more specific shortlist for a G50 with an Guard LSD, tracked only in temps 50-80 degrees F ambient temps?

John

[JohnJL]

How about now?

[Matt Monson]

Sorry,
Never saw that follow up question last time around. For G50?
I would shorten that list to:
Delvac
LUbrication Engineers
Motul
Miller (not previously mentioned but a great oil that has recently started being imported from the UK).

[porschetub]

Gear oil is an extreme pressure lubricant and regardless of brand it is how the oil can still hold it's viscosity @ high temperature and still provide a cushion of oil between gears and sychromesh parts,thats the bottom line ,non ferrous metal parts in the system suffer more due to expansion rates that are very different.
So high temperature is the enemy so it's best to keep it down ,this case may point to other issues inside the gearbox ,don't know ,but not the sort of g/box you want to be fixing often $$$$$.