The Unofficial "Ask a Stupid Question" Thread

I use whatever the owner's manual says to use as that was the standard when the car was built. Especially for pre-E10 cars.

See also: 5W-30 vs 5W-20.
 
I filled the diff with 75w250 back in 2019 and have had no problems, they aren't picky. The limited slip chatters sometimes on tight turns so it could probably use some friction additive.

Red Line Heavy ShockProof® Oil - 58204 - raceparts.com

Buy all your Red Line Heavy ShockProof® Synthetic Gear Oil from us at Raceparts USA, highly rated LSD oil, available with UPS delivery.
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It's probably due for a change, so going to switch back to Mobil 1 75w140 since it has the friction additive in it.

For an open diff use whatever's on sale.
 
I use 75w90. Like said it’s not picky, I used to use 75w140 but it’s just not necessary. With an open diff it can last virtually the life of the car without changing. LSDs with friction modifier and worn off clutch particles it’s best to replace periodically(still like 50,000 miles or more really)

Kenz said:
I filled the diff with 75w250 back in 2019 and have had no problems, they aren't picky. The limited slip chatters sometimes on tight turns so it could probably use some friction additive.

Red Line Heavy ShockProof® Oil - 58204 - raceparts.com

Buy all your Red Line Heavy ShockProof® Synthetic Gear Oil from us at Raceparts USA, highly rated LSD oil, available with UPS delivery.
www.race-parts.com

It's probably due for a change, so going to switch back to Mobil 1 75w140 since it has the friction additive in it.

For an open diff use whatever's on sale.
Click to expand...

I don’t like diff oils that have a premix of friction modifier, the ratios are always off(and usually too much). Last time I put in the cheapest parts store brand of plain 75w90 and HALF bottle of motorcraft friction modifier. Strong lockup and no real chatter
 
At 239,000 I have yet to change the fluid in the Mark... :zwall:

I think I used Valvoline 75W90 with friction modifier when I put the TL 3.73 pumpkin in the T-bird. It's been fine so far but I guess it'll be time to replace it soon.
 
I need to yank the diff on Lazarus, and rebuild it. At 550k miles, I've never changed the oil. Or had problems. It left two black marks, the last time I drove it, rod knock and all.:)
I'm still amazed that it didn't break until I put it back in its parking place.
 
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