Maximum temperature for gear oil

[CTTitan]

I've searched around and have not found an answer to this question.

What is the maximum temperature that a synthetic 75-140W gear oil is good for?? How about regular non synthetic gear oil??

I have measured temperatures of up to 260 degrees in my rear diff and I wonder what the maximum safe temperature is??

 

[mechtech]

Wow!
That seems really warm for a rear end.
That is very hot even for an engine.

 

[CTTitan]

quote:

---

Originally posted by mechtech:
Wow!
That seems really warm for a rear end.
That is very hot even for an engine.

---

These temps were taken with a IR temp monitor when I was towing my trailer with outside temps in the mid 90's and very steep hills (Hwy 49 in California). I have recently checked the temps using a surface mounted RTD and it was running 180-190 while towing with a high of 210 degrees after pulling a good grade on the interstate.

 

[mechtech]

If you are getting those high temps on Hwy 49, I'd back down to Hwy 48, or 47!

 

[Doug Hillary]

Hi,
CTTitan - Eaton conducted tests on oil/component durability during the late 1980s early 1990s

Their intent was to maximise seal and gear life and to allow the maximum OCI possible for their Heavy Truck gearboxes and diffs when using 75w-90 and SAE50 gear oils

They found;
a) components should not be operated at consistent temperatures above 250F
b) Intermittent operations to 300F do not harm the components or oils (synthetics)
c) Oils with a sulphur/phosphorus additive package activate rapidly above 230F.
d) A poor additive package in a synthetic lubricant may not be as good as a good (thermally stable) additive package in a mineral oil

My experience is that synthetic gear oils (75w-90 and SAE50) usually reduce operating temps by from 10-20C

I constantly run 1m kms (620k miles) OCIs with synthetic lubricants in gearboxes and diffs
with excellent results

I moved from 80w-140 mineral oils to 75w-90 synthetics in diffs because we never measured temperatures above 102C and took the benefit of the lighter oils
In cars/SUVs and Utes I have found most diff temps are around 60-75C on mineral oils. A change to synthetics brings this down by about 5-15C

Regards
Doug

 

[XS650]

quote:

---

Originally posted by Doug Hillary:

c) Oils with a sulphur/phosphorus additive package activate rapidly above 230F.


Regards
Doug

---

Is c) good or bad? Sounds good.

 

[wrangler]

I've measured my diff (Dana44) with an IR after cruising at about 75mph for an hour and it was about 160F. but that is without towing anything and driving on a flat road...

 

[Doug Hillary]

Hi,
X650 - good!

Eaton also found that they could recommend five times the mineral OCI with synthetics
They also found the average seal replacement in fleets using mineral oil was 150k miles. At that period in their testing with synthetics that the average was zero

That has been my experience too with seal replacements being zero in service(except at brake lining time as before)over many millions of kms

At the time (about 1995) my initial move from a 80w-140 synthetic to a 75w-90 synthetic caused some drama here in OZ. I had to seek special written approval from Eaton & Rockwell in the US (for Warranty) even though both approved the ligher viscosity for "All temperature ranges" in the US. They argued here in OZ that it was the "shock loading" factor - we had many arguments. Written approval was given via the US of course and now many fleet owners use the lighter viscosity synthetic here. It is now a factory fill

Of course we have never had a failure of any sort

This is/was all part of educating "the experts"

Regards
Doug

[ July 20, 2005, 05:42 PM: Message edited by: Doug Hillary ]

 

[tdi-rick]

always informative, Doug !

 

[Gurkha]

Speaking of tranny temps, I have a Nissan Patrol which is based on the 69 model, it was made for the Indian military toll the year 2000. Mine came with 4 cylinder 11ton rated HINO diesel but sadly the rest of the package still remains 1969 vintage including the puny 3 speed gear box. The HINO engine at through two gearboxes and only the last one has lasted over 100,000 miles, you should see the smell that comes from it when the vehicle hits 100mph which is really in the red zone, even with normal driving, it reduces SAE90 gear oil to thin water in under 5000 miles, I have been forced to use 85W-140 mineral based GL-5 oil in it, I also double clutch to preserve my synchros.