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Discussion Starter #1
I know the spec is 2.5 quarts. Anyone putting more in to get added cooling and protection in long sweeping terms? Will it leak if you do so? I have a hybrid 8.8 with 9 inch ends.
 

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I fill mine up to where I can reach the oil with my pinky which happens to be the specified amount and I still get a little coming out of the vent on the right side.
 

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Would more fluid actually equal better cooling without an external cooler or fins (heatsinks) built into the diff cover?
 

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Discussion Starter #5
I would think adding extra fluid would aid somewhat in cooling because you would be increasing the heat sink somewhat?

I had to pull the axles to replace the bearings which got me thinking about fluid capacity. My axles tubes do not have any internal seals in them. It seems like most of the fluid could run to one side or the other in a long sweeping turn and starve the differential. I have a DPI Black Gold differential. The unit took approximately 2.75 quarts before fluid began to flow from the front fill port. As a data point, I have a catch can that is angled in such a way as to drain back into vent line so I never lose any fluid. I called Griggs and spoke with Bruce. He stated that they run the OEM capacity and that overfilling it will result in leaks. It appears that the OEM capacity is enough to keep the differential lubed based on my research.
 

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Adding alum diff cover / girdle adds legitimate fluid capacity and promotes cooling. You do not want to overfill your diff - if it leaks and ruins a set of brakes that sux.

Temp is of course determined by time/speed and tire height/gear ratio as well.

Be mindful of the fluid used. Lots of new synth fluids have less heat transfer capacities than the traditional dino based lubes. Hypoid gears present really heavy shear loads on the lubricants also.

I run an Eaton TrueTrac (Torsen style) diff and use old school conventional 85W140 with a 3.73 gear and a girdle. I think it holds 3 pints now.
Not a bad idea to change it fairly regular basis, just like all automotive fluids.

I call that cheap insurance, and you get a good look at the conditions of all your systems.
 

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Since the fill method is to add fluid until it starts to back out of the fill hole, how could you over fill it? I would think the only way you could have more fluid is to use an aftermarket cover that was designed to allow more fluid capacity. In any event I run a stock cover in my IRS and run the s*** out of it on the track with no issues. If you have a cooler you would probably have to fill your diff., close it up, run the car, then add more fluid to make up for the fluid that fills the cooler and lines.
 

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Discussion Starter #8
Since the fill method is to add fluid until it starts to back out of the fill hole, how could you over fill it?
. My cover (Griggs) has a fill hole up top in addition to the standard port at the front of housing. I suspect I could easily get 5-6 quarts in there if I wanted to.
 

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That's probably a convenience port--easier to get a filler to than the standard port. You'd probably do best to open the standard port and fill from the convenience port to avoid overfilling.
 

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Discussion Starter #10
Yes. That is exactly what I did.
 

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. My cover (Griggs) has a fill hole up top in addition to the standard port at the front of housing. I suspect I could easily get 5-6 quarts in there if I wanted to.
The prior owner of my car filled the diff too the top of the fill port. There was oil everywhere.
 
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