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So, for this weekend's Alfa Cup race I had added a transmission oil temperature gauge to the 3.0 Milano/75 budget race car (engine + electronics out of a 164S, completely gutted). These are 20-30 min sprint races. Shifting was around < 6000 RPM with max speeds around 120 MPH in 5th. It is a 4.10 gear box with 50% lock-up, and I run Redline 75/90 NS - heel and toe + double clutching.

1. What transmission oil temps would you expect?
2. At what temps would a cooler become necessary?

Jes

Don't be a tease tell us the temp!

I have seen 130*C in my gearbox after a few laps, that's where it stopped climbing and I'm planning to add a cooler next year actually. around 120-130 I think the oil is starting to degrade very rapidly, you can have higher temps but you will need to change the oil more often.

Ok, ok. I was just curious to see if anyone realizes the level of the temps. I was seeing the gauge maxing out at 250F (~121C) towards the end of sessions. Are you saying that these temps are ok as long as oil is changed more frequently? I was concerned that it could cause excessive wear even with fresh oil if you cross certain temps...??? I got a fresh gearbox in the car and want it to last...
Jes

That will be quite ok I believe, gearboxes tend to run rather hot compared to engine operating temps.

From the Redline webiste http://www.redlineoil.com/whitePaper/10.pdf you can see that the viscosity is 15.6 at 100C and goes down to 6 at 150C for the 75-90. Generally, you would need a cooler if you go below 10. I think 120C is okay, however, as you are topping the gauge it is possible that the temperature is higher than that, i.e. 130+ which is probably too much. Also the localized temperatures can be higher than the average... Where did you mount the sensor (I know I've read about it, but can't remember )

Drilled and tapped plug. Hmm, maybe it is time to add a cooler. If I recall correctly AR did run a tranny cooler on the SZ, right?
Jes

Yes. SZ has oil cooler. Pump mounted in gearbox front part and cooler mounted on the inclined section beneath rear seats (pic). Probably not the best way to do that as the cooler can be easily damaged while racing. Another way is shown in pic2.
Another option would be to move to outboard rear brakes. The racing 75s didn't have a trans cooler AFAIK.

Like the 2nd picture I would "take" the transmission oil from a fitting on the drain plug and return it to a fitting on the fill plug. Mocal makes a suitable pump - I'm sure there are many others. On my race car the space under the trunk floor is completely empty. A cooler could sit fairly well protected under there. I have no plans of going to outboard rear brakes on this car. I don't even seem to have a need for vented rears.
Jes

Jes, I think you know that Nizam has been putting many track miles on his 12 valve car. It seems as if he's been getting along just fine w/o cooling his transmission oil.

Maybe you have more invested in your transmission than he does?

grant wrote:Maybe you have more invested in your transmission than he does?

I don't think so, but it is a relatively fresh transmission. I think Nizam's is mostly street miles and some track events. I'm not sure if he has years of heavy track and race use on a single transmission to provide a valid data point. I have previously done time trials in a stockish 3.0 Milano, and this seemed to cause some accelerated wear over 2-3 years. Is this natural , or could it be prevented? That's why I decided to at least measure the temp to see what conditions the oil and box are subject to.
Jes

Did you actually see wear on the gearset or do you mean wear as in synchros?

I'm still running that box in my street car, so it is a non-scientific statement. So, this is purely by feel in terms of syncro wear. During that time the car did not see a lot of street use.
Jes