Diff cooling and E85 results - interesting findings at Road Atlanta - fast lap

[ScottD]

I’ve been struggling with differential overheat issues on my “time attack” Mustang GT. I’ve wrapped the exhaust and have been running a diff cooler. Still at Sebring last month, diff temps climbed to just shy of 300F in the afternoon sessions. I was running royal purple 75w140. Fast forward to February. Last weekend I ran with Chin at Road Atlanta, my home track. Changes to the car included switching to Redline 75w110 for diff fluid and switching over to E85. I purchased my E85 tune (dedicated E85 tune, not flex) from Wengerd Performance. Also splurged and took VP racing X85 to the track in those 5 gallon pails. Highest diff temp I saw all weekend was around 260F. Ambient temp in the afternoon was about 62F which was slightly cooler than Sebring. Still I believe the combination of the Redline fluid and E85 (which should lower EGT - exhaust gas temp) may have resulted in the lower differential temp, as a lot of folks blame the closely routed exhaust for the diff heat soak, which, I believe is true.
I was also very pleased with the performance on E85 as the car had noticeable improvements in torque and seemed to rev more freely throughout the rpm range. At Road Atlanta, on the back straight, I usually go to 5th gear as 4th seems to flatten out at the top of the tach. That shift to 5th seems natural for the car. However on E85, the power kept coming and I instinctively kept 4th gear all the way to the braking point before 10a. On E85, that combination increased my top speed to 147mph on the back straight (up from 138mph). Personal best lap time posted in at 1.34.76 down from 1.36.85.
I’m very pleased with the E85 other than the cost of the VP fuel at over $11 per gallon to get pure E85. My local pump gas is testing at 75% E right now. Wengerd says the car will adjust within a certain range and running E75 on the dedicated E85 tune wouldn’t be a problem. I don’t fully understand what all happens in the ECU and how things adjust . I guess, worse case, the car will be running a little rich on the lower content E75 fuel. At WOT, that shouldn’t be much of an issue.
Comments, Questions and Suggestions are welcome

 

[JDee]

I used to get axle overheats on hot days. I switched to Redline 75W140 and they stopped.
But.
You should put a diff cooler in if you haven't already. This is a problem that will destroy your diff, even the Torsen diff and even with 75W140 lube. I waited too long to put a cooler in and the diff was junked.

 

[JAJ]

I’ve been struggling with differential overheat issues on my “time attack” Mustang GT. I’ve wrapped the exhaust and have been running a diff cooler. Still at Sebring last month, diff temps climbed to just shy of 300F in the afternoon sessions. I was running royal purple 75w140. Fast forward to February. Last weekend I ran with Chin at Road Atlanta, my home track. Changes to the car included switching to Redline 75w110 for diff fluid and switching over to E85. I purchased my E85 tune (dedicated E85 tune, not flex) from Wengerd Performance. Also splurged and took VP racing X85 to the track in those 5 gallon pails. Highest diff temp I saw all weekend was around 260F. Ambient temp in the afternoon was about 62F which was slightly cooler than Sebring. Still I believe the combination of the Redline fluid and E85 (which should lower EGT - exhaust gas temp) may have resulted in the lower differential temp, as a lot of folks blame the closely routed exhaust for the diff heat soak, which, I believe is true.
I was also very pleased with the performance on E85 as the car had noticeable improvements in torque and seemed to rev more freely throughout the rpm range. At Road Atlanta, on the back straight, I usually go to 5th gear as 4th seems to flatten out at the top of the tach. That shift to 5th seems natural for the car. However on E85, the power kept coming and I instinctively kept 4th gear all the way to the braking point before 10a. On E85, that combination increased my top speed to 147mph on the back straight (up from 138mph). Personal best lap time posted in at 1.34.76 down from 1.36.85.
I’m very pleased with the E85 other than the cost of the VP fuel at over $11 per gallon to get pure E85. My local pump gas is testing at 75% E right now. Wengerd says the car will adjust within a certain range and running E75 on the dedicated E85 tune wouldn’t be a problem. I don’t fully understand what all happens in the ECU and how things adjust . I guess, worse case, the car will be running a little rich on the lower content E75 fuel. At WOT, that shouldn’t be much of an issue.
Comments, Questions and Suggestions are welcome

You might want to switch back to the diff oil the car came with. Ford runs 75w-85 diff oil in the FP Shelby's because it generates less heat under high load than heavier oils and it lubricates at least as well or better. It's a modern formulation developed to meet a very tough spec published by Ford in 2012. Don't assume that because it's OEM, it cant' be as good as the best aftermarket products.

 

[Paul McWhiskey]

You might want to switch back to the diff oil the car came with. Ford runs 75w-85 diff oil in the FP Shelby's because it generates less heat under high load than heavier oils and it lubricates at least as well or better. It's a modern formulation developed to meet a very tough spec published by Ford in 2012. Don't assume that because it's OEM, it cant' be as good as the best aftermarket products.

Correct. Found this occasionally in industrial settings. Very often when a gear box was running hot someone who did not know better would put a heavier ( higher viscosity ) lubricant in it with the thinking that it would lower operating temperature. More often than not this would not work. The solution would be to drain the box and refill with the correct grade of lubricant. And op temps would usually return to normal unless there were damaged or worn out parts in the gear case.

Viscosity grades are determined by load and speed. If a very high viscosity lubricant is used in place of a lower viscosity lubricant, its ability to remove heat from the gear set is actually lower because it cannot flow ( weather that is splash or pressure lubrication ) as easily to remove the heat from the gear set. The spec lubricant for any gear set is usually robust enough to handle keeping the gear faces from touching each other and removing the heat that is generated by the gear set and lubricant. That said, most Mustangs were not designed for continuous track duty. The best answer for removing this type of heat from the differential is an external diff cooler. IF you can remove the excess heat from the diff you can run it up to its designed load limit safely. Once you have exceeded the design load limit all bets are off.

So, a Mustang making 600hp or more along with the associated increase in torque (actually more important here ) needs additional diff and probably trans cooling. Higher viscosity lubricants might mask the heat rise for a short while, but could be actually adding to the problem due to lower flow characteristics that reduce the ability of the lube to transfer the heat from the gear face to the case or cooler and overboard. Adding coolers adds cost and weight. But it is also going to add life to whatever it is plumbed to which is usually more expensive than the cooler to replace.

I have watched the lube threads for quite a while and struggled with the 75-85 or 75-140 gear oil question the whole time. My training and experience with heavy and industrial equipment tells me “No” don’t do it. In doing the job that the car is designed for ( not racing ) the specified lubricants work. Once the car is used for racing it becomes necessary to add ways to dump all of the excess heat that is generated to maintain some modicum of reliability or failure is guaranteed.
With all of this said, I think that most will try the route of adding the wrong lubricant or the magic mechanic in a bottle before spending the money for external coolers which ultimately is the answer in order to use the differentials or transmissions that these cars come from the factory with for racing.

In the end, it is heat that is the enemy of all things mechanical. Every effort to keep that heat from getting in and getting it out of any power producer or transmitter should be considered. Then utilized in order of efficiency. And by efficiency I am not referencing how easy it is to do.

 

[JAJ]

Correct. Found this occasionally in industrial settings. Very often when a gear box was running hot someone who did not know better would put a heavier ( higher viscosity ) lubricant in it with the thinking that it would lower operating temperature. More often than not this would not work. The solution would be to drain the box and refill with the correct grade of lubricant. And op temps would usually return to normal unless there were damaged or worn out parts in the gear case.

Viscosity grades are determined by load and speed. If a very high viscosity lubricant is used in place of a lower viscosity lubricant, its ability to remove heat from the gear set is actually lower because it cannot flow ( weather that is splash or pressure lubrication ) as easily to remove the heat from the gear set. The spec lubricant for any gear set is usually robust enough to handle keeping the gear faces from touching each other and removing the heat that is generated by the gear set and lubricant. That said, most Mustangs were not designed for continuous track duty. The best answer for removing this type of heat from the differential is an external diff cooler. IF you can remove the excess heat from the diff you can run it up to its designed load limit safely. Once you have exceeded the design load limit all bets are off.

So, a Mustang making 600hp or more along with the associated increase in torque (actually more important here ) needs additional diff and probably trans cooling. Higher viscosity lubricants might mask the heat rise for a short while, but could be actually adding to the problem due to lower flow characteristics that reduce the ability of the lube to transfer the heat from the gear face to the case or cooler and overboard. Adding coolers adds cost and weight. But it is also going to add life to whatever it is plumbed to which is usually more expensive than the cooler to replace.

I have watched the lube threads for quite a while and struggled with the 75-85 or 75-140 gear oil question the whole time. My training and experience with heavy and industrial equipment tells me “No” don’t do it. In doing the job that the car is designed for ( not racing ) the specified lubricants work. Once the car is used for racing it becomes necessary to add ways to dump all of the excess heat that is generated to maintain some modicum of reliability or failure is guaranteed.
With all of this said, I think that most will try the route of adding the wrong lubricant or the magic mechanic in a bottle before spending the money for external coolers which ultimately is the answer in order to use the differentials or transmissions that these cars come from the factory with for racing.

In the end, it is heat that is the enemy of all things mechanical. Every effort to keep that heat from getting in and getting it out of any power producer or transmitter should be considered. Then utilized in order of efficiency. And by efficiency I am not referencing how easy it is to do.

Exactly. The OP says he has a diff cooler so the spec lube that Ford puts in the high horsepower, high torque, cooler-equipped GT500 should work fine.