100 Series Diff Oil (1 Viewer)

Joined
Feb 6, 2010
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So a couple weeks ago, the rig was up on a friend's lift and we noticed the rear diff was weeping a little oil out the top plug.

Today I decided to replace the crush washer and while I was at it, called the dealer to check to see what oil they'd recommend to top things off (just checkin').

When I asked if I should use dino or synthetic, the parts or service manager said, "Definitely dino - don't mix the existing dino with synthetic - and get a 75 to 90 GL-5 oil."

No surprise since that's what is recommended, but wondered why they'd be adamant about not mixing the two??

Also, since it was last changed at the dealer w/ dino, at that time they seemed to discourage use of synthetic oil for both diffs and the t-case. Next service interval I want to change over to synthetic, but in both instances (last service and again today) their comments made me wonder why they'd discourage it.

Anyone know of any issues running synthetic in both diffs and the t-case? Either full on or mixed?
 
Joined
Feb 9, 2013
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There are no issues that I'm aware of with synthetic. However, I have seen some diffs "grind" a little after fluid change and needed friction modifier added. Just for consistency and to eliminate any potential issues with different types of fluid, I personally wouldn't consider the use of synthetic diff fluid. Plus, the non-syn lasts a long time if you keep it changed at least every 30k miles.
 
Joined
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Raleigh, NC
Interesting, I have always run Amsoil full synthetic in all my diffs, t cases, and transmissions. Never ever had a problem with anything. I wonder why he was so adamant about Dyno oil.
 
Joined
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Did a little reading on BobIsTheOilGuy.com last night. Seems that some of the reasons given for not running synthetic include:
  • Specific gear and axle specifications
  • Towing
  • Shop profit margins
  • 4x4
  • Water crossings vs. mall cruising
Nothing really specific to Toyota or Land Cruisers though. A few "expert" comments from fleet managers who swear by synthetics too.
 
Joined
May 7, 2005
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South Jordan, UT
I don't think the diffs will really see any benefit from synthetic lube. They don't get that hot, and as was said above, the dino stuff stays in spec for a long time.
I've always taken the stance that the diffs are one of the most likely places to see fluid contamination, so I change them out a couple times per year. Definitely no reason to go syn under those conditions.
 
Joined
Nov 13, 2015
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Texas
There are no issues that I'm aware of with synthetic. However, I have seen some diffs "grind" a little after fluid change and needed friction modifier added. Just for consistency and to eliminate any potential issues with different types of fluid, I personally wouldn't consider the use of synthetic diff fluid. Plus, the non-syn lasts a long time if you keep it changed at least every 30k miles.
I replaced my diff fluid with royal purple synthetic. It was running fine before and now its popping and chattering a bit. This issue started immediately after I changed the diff fluid. Just FYI....
 
Joined
Feb 9, 2013
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I replaced my diff fluid with royal purple synthetic. It was running fine before and now its popping and chattering a bit. This issue started immediately after I changed the diff fluid. Just FYI....

Interesting, are you going to put "regular" fluid back in it and see if it fixes it? I change the diff fluid every 30k with nonsynthetic and have had zero issues.
 
Joined
Nov 13, 2015
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Texas
Interesting, are you going to put "regular" fluid back in it and see if it fixes it? I change the diff fluid every 30k with nonsynthetic and have had zero issues.
I have the vehicle at the dealer right now. Yes replaced it w manufacturers fluid w additive.. Gonna see how that works but dealer said they drove it and still doing it..
 

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