Question on Synthetic Gear Oil Flash Point

[R80RS]

I’m looking at synthetic gear oil for my F150 rear differential, and I see the following flash point data (from manufacturer’s product bulletins):

AMSOIL Severe Gear Synthetic 75W-140 ----------------> 210C
Mobil 1 Synthetic Gear Lubricant LS 75W-140 ----------> 207C
Pennzoil Synthetic 75W-140 ------------------------------> 188C
Valvoline SynPower Full Synthetic Gear Oil 75W-140 ---> 173C

Data for other parameters (what there is of it) seems relatively comparable between the products.

I generally hold Valvoline products in high regard. Is the low flash point on the Valvoline a reason to not consider it? What is the general opinion in BITOG-land of Valvoline’s gear oils, and which of these (or something else) would you specify?

 

[spasm3]

Afraid your rearend might get to 350 F?

 

[R80RS]

Originally Posted By: spasm3
Afraid your rearend might get to 350 F?


I'm wondering why one oil I'm considering has a significantly lower flashpoint than similar oils and I'd like to learn something about gear lubrication in the process.

 

[Nederlander75]

My diff hit 280f last (2012) July one lapping day according to a probe and ir.

 

[INDYMAC]

Originally Posted By: R80RS
Originally Posted By: spasm3
Afraid your rearend might get to 350 F?


I'm wondering why one oil I'm considering has a significantly lower flashpoint than similar oils and I'd like to learn something about gear lubrication in the process.


If you ask the manufacturer which method they use to determine FP, you might find your answer. Good luck!

 

[GSCJR]

Let's not forget those temperatures are in Celsius.

 

[Whitewolf]

Have you thought that perhaps the Valvoline might be Group III? Which can legally be described as synthetic.

 

[jake88]

Flash point is dependent on what vapor exists directly above the fluid level. It is approximately equal to the lowest flash point component - adding other higher flashpoint fluids does not increase it significantly.

Since all those fluids are synthetic, there may be a difference in their method for determining flash point, as there are many ways to do so (Cleveland Open Cup, Tag Closed Cup, Estimation from components, etc.) There may also be differences in their formulation strategy - one brand could be using very thin base oils with slightly lower flash and a more shear stable thickener, for example.

Really, though, for closed systems like a differential it is has no bearing on performance. It really gets important when you are talking about open circulation or gearing systems, metal removal fluids, or other workplace industrial lubricants where OSHA wants flammability hazards classified.

 

[Whitewolf]

I agree totally with what you are saying. Unless you know what test method was used it's almost impossible to make a comparison and as you rightly point out the formulation strategy can affect the outcome unless there are other test constraints in the specification that already cover that. Either way I don't see this as an issue in a rear diff, the most I have seen even on the Baker Grade test is about 400F.

 

[T_CUDA]

I use Valvoline Synthetic in all my Jeeps and Work trucks. It meets the U.S. Mil. Spec and that is plenty good enough for me.

 

[R80RS]

Originally Posted By: jake88
Flash point is dependent on what vapor exists directly above the fluid level. It is approximately equal to the lowest flash point component - adding other higher flashpoint fluids does not increase it significantly.

Since all those fluids are synthetic, there may be a difference in their method for determining flash point, as there are many ways to do so (Cleveland Open Cup, Tag Closed Cup, Estimation from components, etc.) There may also be differences in their formulation strategy - one brand could be using very thin base oils with slightly lower flash and a more shear stable thickener, for example.

Really, though, for closed systems like a differential it is has no bearing on performance. It really gets important when you are talking about open circulation or gearing systems, metal removal fluids, or other workplace industrial lubricants where OSHA wants flammability hazards classified.


Thanks for an intelligent answer. Seems odd that a manufacturer would choose a test method that yields a lower result, particularly for data used in marketing information. Regardless, sounds like there may be valid reasons for Valvoline's lower number that don't call the product quality into question.

 

[Garak]

Originally Posted By: R80RS
Seems odd that a manufacturer would choose a test method that yields a lower result, particularly for data used in marketing information.

Fair enough, but how many people really use such data to determine which product they're going to buy? Ideally, the first thing they should be looking for is compliance with the specifications for their application. After that (or even before that) cost will be king.

 

[R80RS]

Originally Posted By: Garak
Fair enough, but how many people really use such data to determine which product they're going to buy?


For the sort who hangs out on BITOG chances are good that a large number would at least consider it. Among the general public, probably not so much.

The variation in this one parameter among these four oils caught my attention, particularly since the other reported parameters were so similar. FWIW I did end up buying the Valvoline, based on price and a recommendation by someone whose opinion I value.

 

[Garak]

I'd have no problem using the Valvoline, either. Like has already been mentioned, there are different ways to determine flash point, and we see all kinds of strange things in UOAs to illustrate that.

 

[metroplex]

I found this thread while researching flash point of gear oil. As you know the Ford PTU's for AWD vehicles can get very toasty as they sit above catalytic converters and their is limited fluid inside of the case. The highest flash point I found for a 75W-140 is 489F (Schaeffer's) but can't find much data for any gear oils that may have a higher flash point. I'm just trying to find the best 75W-140 that can handle the highest temperatures possible.

 

[MolaKule]

Originally Posted by metroplex
I found this thread while researching flash point of gear oil. As you know the Ford PTU's for AWD vehicles can get very toasty as they sit above catalytic converters and their is limited fluid inside of the case. The highest flash point I found for a 75W-140 is 489F (Schaeffer's) but can't find much data for any gear oils that may hPTU's ave a higher flash point. I'm just trying to find the best 75W-140 that can handle the highest temperatures possible.


Those Ford PTU's have limited cooling and fluid capacity which is a problem.

The best you can do is monitor the fluid and change as often as is practical.

 

[metroplex]

MolaKule,
Would running a gear oil with a higher flash point help? Schaeffer's 167 and 170 in 75W-140 appear to use PAO and have a high flash point (489F) versus everyone else. Amsoil Severe Gear 75W-140 has a flash point of about 410F.

From my research, I've found there are 2 distinct PTUs used on the Ford SUV/cars. One type of PTU is used on the smaller SUVs and/or SUVs with smaller engines. Escape, Fusion (even the Sport w/ 2.7 Eco), and Explorer with 2.3 use a design that doesn't as hot or have as many problems reported. The other type is used on the Explorer/Taurus/Flex/etc... with the 3.5L V6 (either N/A or EcoBoost). Ford made a running change in June 2016 where it was the 3rd revision for the idler gear system. I guess it is still too early to tell whether it solved the problem with the idler gear running into the case, but the first 2 changes didn't seem to make an impact.

My Fusion Sport PTU has a Torx-Plus drain plug and a fill plug, with a cooler installed at the lower part of the PTU case (looks like a heat exchanger that is inserted into the case).
My 2018 Explorer, and my previous 2014 SHO, use a PTU that only has a fill plug. But the Explorer Sport/SHO with Perf Pkg / Police Interceptors have a cooler that seems to only cool that part of the case and not the bulk of the fluid.

 

[ad244]

Originally Posted by T_CUDA
It meets the U.S. Mil. Spec and that is plenty good enough for me.


So its the cheapest option possible?

 

[MolaKule]

Flash points are not the issue.

The issue here is the limited cooling and small capacities which means the oil is thrashed by shearing and oxidized by heating.

Amsoil SevereGear or Schaeffer's #170 may extend your OCI's.

Again, The best you can do is monitor the fluid and change as often as is practical.