: Synthetic or Dino Diff oil?

11-17-2008, 06:17 PM
I've been using Synthetics for years. I read somewhere that some dealership service areas are switching back to Dino oil in diffs because they have experienced alot of breakage with Synthetics. They seem to feel that Dino oil protects better. Has anyone heard this before?

My son needs to do his diffs and isn't sure what to use?

11-18-2008, 12:36 AM
i have never heard that. i use synthetic, it works fine for me

11-18-2008, 01:24 AM
thefatkid was telling me a little about this. I think he said the seals were not as compatible with synthetic and they have seen some increased leakage from people running synthetic, and they use dino only.

It seems that I don't really get to take advantage of extended drain intervals, so I will probably just do dino when it comes time.

11-18-2008, 04:32 AM
I was also told what Troy just stated.

11-18-2008, 09:21 AM
I know synthetics don't thermo break down. If you do the recomended changes does it matter? Most vehicles come from the factory with Dino.

11-18-2008, 10:22 AM
Its not the synthetic oils it's the seals that are'nt compatable

11-18-2008, 10:49 AM
Its not the synthetic oils it's the seals that are'nt compatable

So are there seals you can get that are compatible with the synthetic fluids?

11-18-2008, 10:59 AM
I have never had a problem with synthetic oil & seals, ever. I know a few people who have experienced leaking seals with dino oil.

So I wouldn't say it's conclusive.

What is worth mentioning is that some of those synthetics are not viscous enough to climb the ring gear and properly lubricate the differential.

I'm running 85/140 dino in the rear differential, and 75/90 synth in the front diff and t-case for that reason, but I don't have a stock rear diff. I ran 75/90 synth for about 100k miles without any seal problems in the rear diff, and have about 120K on synth in the front diff and t-case.

I would not expect any problems running 75/90 synth in a stock rear end, and I don't think there's any need to run the 85/140 dino that I'm using, if you have a normal Toyota rear diff.



11-18-2008, 12:17 PM
I've been running Valvoline 75-140 Synthetic in my diff for roughly 3500 miles now, i had a slight leak from one of the outer axle seals at first, replaced it and i havent leaked a drop since.

All of the seals are pretty new though (roughly 10k miles)

11-18-2008, 12:43 PM
I've never had a mechanic recommend synthetic, and several that I trust recommend Dino. I've never argued the point and the only diff problems I've had are more likely attributed to off-road driving than fluid. I've run nearly 500,000 miles on the various Toys I've had, never used synthetic and never had diff issues until the FJ, but again, more likely the ridiculous number of trails I've driven the last 2 years.

11-18-2008, 12:49 PM
Sean - you want something that sticks and will climb the ring gear, try Redline Heavy Shockproof!

11-18-2008, 02:16 PM
The seals were updated in late 03 to a more synthetic friendly design. The previous seals were know to leak when synthetic oil were used. Synthetic oil is supposed to carry the same weight ratings as their dino cousins but are often under rated. Lubrication ratings equal the dino ratings at a thinner oil level, ok for the bearings, not ok for the seals.