Engine and gearbox oil specs comparison

[madbilly]

Hi all,

I know there's a LOT to consider when thinking about whether or not a certain oil is suitable to use or not. I've read all the advice on here and loads more from around the web that all pointed to two things:
1. Synthetic is always best (but not all sythentics are considered as such by everyone)
2. The base specs of winter grade and "summer" grade are very coarse, as there's a lot of variation within each band.

From my point of view the first point is addressed by making sure the oil calls itself "synthetic" not "part" or "semi" or similar. For the second point I decided I'd compare the more technical specs of various oils against the spec of the Lotus "alternative" spec of Mobil 1 Rally Formula 5w50 (because the "preferred" and other "alternatives" were too loose a spec, not being a single particular oil). I found that (of the one's I checked) Comma Motorsport 5w50 was the closest match.

I know that just because it's the closest match it doesn't mean that it's the best suited to my engine after 20+ years and 100k+ miles, or that it's best suited to my driving style and typical usage - it's very likely that other oils will be more suitable. However, having done the comparison I found that Comma Motorsport 5w50 was nicely priced and since I started using it I've not had any problems, but then I have only covered a few hundred miles.

I did the same for the gearbox oil and found that (as expected) Castrol Syntrans Transaxle was the closest match to the recommended Castrol TAF-X (I didn't compare against the original Mobil 1 RTS 9775 because I couldn't find a spec for it).

See attached for the detail of the specs. I'm not professing any competence in this area, I'm just an enthusiastic owner like the rest of you.

Cheers,
Will

[tigerdog]

Nice work! I know a number of us use Redline synthetic in the transmission, so I've updated the sheet to include the specs for Redline MTL and MT-90. Wish I'd seen this info before I drained/refilled; turns out the Castrol synthetic is readily available in the US. If nothing else, I can report Redline MT-90 is a bit more viscous than the original but boy does the car shift well.

[ccb056]

I'm actually planning a gearbox oil change for later this week.
I spent the past couple weeks researching this topic and this is what I found:

Engine oil viscosity is different than gearbox oil viscosity
The US owners manual lists Mobil 1 RTS 9775 (5W30 Gl-4), not sure about the S2 but it may recommend Castrol TAF-X, can someone confirm/deny?
Called Mobil 1 tech line, their engineers could not find this oil in the computer.
Called numerous Lotus dealerships, received mixed answers (any oil will work, Redline MT90, Redline MTL, Castrol TAF-X, a few dealers even found LEC on Google and were reading from this site)
Called Dave Bean Engineering, they have 1 quart of Castrol TAF-X 75W90 GL-4.
Castrol TAF-X is a UK formula, it is not sold in the US.
Castrol Syntorq LT SAE 75W-85 API GL-4 is the US version of TAF-X, it is sold to GM dealers under part number 12346190 and Chrysler under part number 4637579.
Amsoil Gear Lube 75W-90 API GL-4 (MTG) is the replacement fluid for GM part #12346190 and Chrysler part #4874459 (Chrysler specification #MS-9070) Interesting the GM part numbers match, but the Chrysler ones do not
Called Redline and spoke to a tech, they recommended the MT-90 or MT-85. I asked why they didn't recommend the MTL and the response was the MTL was too low viscosity. The owners manual calls for a 5W30 (70/75W80 in gearbox viscosity according to the tech) oil, and the MT-90 is a 15W40. Tech also said to stick to the GL-4 oil and not switch to GL-5 because GL-5 uses friction modifiers that are too slippery for synchros and can be corrosive to brass.

FWIW GM 12346190 is going into the gearbox...

[madbilly]

Thanks for the updates.

All this confusion over recommendations from various suppliers (see the other threads about gearbox oil, engine oil) is why I decided to down to comparing the base characteristics, I figured it was the only way.

[muley]

Oil specs.xls

I've just changed my gearbox oil to Fuchs Syn5 (my son had some left over from his Fiat Coupe days..)

I've added the SYN5 specs to the sheet.

BTW the gearbox seems to be functioning fine - seeing another thread it appears it hardly requires any oil!

Jim

[tb10]

Oil specs.xls

I've just changed my gearbox oil to Fuchs Syn5 (my son had some left over from his Fiat Coupe days..)

I've added the SYN5 specs to the sheet.

BTW the gearbox seems to be functioning fine - seeing another thread it appears it hardly requires any oil!

Jim

[tigerdog]

Updated with several LiquiMoly varieties available in the US. I've used the 5w40 with good results for about 10 years and about 6000 miles