1987 Montero and Castrol Limited Slip 80W-90

[PythonDR]

It's time to drain and refill the rear axle on my 1987 Mitsubishi Montero, which has the factory limited slip differential. I went to the local auto parts store for the appropriate SAE90 GL5 oil, where I spotted Castrol Limited Slip 80W-90 and thought "great! No additive pack to put in". When I got the stuff home and opened the bottle up, I saw that it had neither the color nor the distinctive smell of a gear oil with LSD additive. Yet, the Castrol product sheet on their website says it's suitable for "service fill of limited slip differentials". I do have a bottle of LSD additive, and the question is: should I trust Castrol's product sheet and risk damaging the clutch pack by running it straight, or do I put in the additive and risk having too much friction modifier for the application? Or is there a third option?

 

[Oro_O]

I went through the same thing once for a later/late model trooper. Fill it, and see if it chatters and needs mores additive. If so, add it. If Castrol says it is for lsd units, then yes, you can believe it. If it is enough additive for your particular lsd is a different question. In my case, since the lsd in Toopers typically take more than one bottle of additive, I just put in the lsd oil and one bottle of additive, and all was good.

 

[Nick1994]

The real question is, after 31+ years, does it even have any clutch material left to even be a limited slip anymore? I'd use the Castrol fluid and sleep well at night.

 

[Snagglefoot]

Smell this! Your third option.

 

[Falcon_LS]

If in doubt, return it and maybe grab some DiaQueen LSD Gear Oil. If you can find the Japanese version (P/N 3775610) in the tin can, blended by ENEOS, I would recommend that stuff over the stuff in black quart bottles (MZ320345). It was specifically developed for the Evo's (VIII and IX) transfer case and rear differential, but is factory fill on other vehicles such as the Pajero, L200, etc.