Manual Tranny Oil
 

Ok so, I drive a Yaris. I changed my motor oil to Mobil 1 synthetic. Now I want to change the manual tranny oil to synthetic as well. Will this have an effect on mpg? Second, will using a higher octane gas (factory recommends 87 and I use that) have any effect? Thanks!

On some other cars I had, I had MPG gains using Redline MTL synthetic lubricant in manual transmissions on FWD cars.

Fuel, use the lowest necessary to get the job done. In come cases, pump gasolines with higher octanes will leave carbon deposits in the combustion chamber. Might not be in all applications, but it's just not of any benefit when it isn't necessary.

If the factory calls for 87, run 87. generally (but not universally) you will not gain anything by running premium.

My car is an example of the opposite: it calls for premium but will run fine on regular. however, it runs a little smoother, is more responsive, and get better mpg when running premium because the ECU can advance the ignition timing more. I did the math and it's actually more cost effective ($.01 per mile) to run premium.

I would ask Toyota first. With such a new car, which I would assume still has a warranty, it could void the drivetrain warranty if it somehow causes an issue with wear.

If that isn't an issue for you, give it a shot. Just get something that is a similar viscosity to the original fluid in the car. If you don't shifting when the car is cold can get very difficult.

Check your owners manual for what type of fluid is called for and run the thinnest synthetic you can find that meets the spec. Many manual trans these days use ATF.

Yeah you should have no problem running Mobile 1 Gear Lube in the tranny probably calls for an 80-90 weight like my xB. You will find that it will shift a little different at first so don't try to shift too fast or you may feel some gear grinding until the syncros adjust to the new oil. You probably will see an increase in mpg right after you change the gear oil. Seems the factory gear lube is not that slippery.

The owner's manual and the factory repair manual both specify GL4 or GL5 75W-90 oil and nothing more. So I think I am safe, yes?

yup just read the Mobile 1 can / bottle and don't over fill it! Make sure you open the filler plug before you drain the tranny because you can't put more oil in after you drain it if you can't open the plug.

Use the GL-4. I'm not *sure* about the Yaris, but in the xB the GL-5 is actually corrosive to the brass synchros. Plus the GL-4 is a slightly lighter weight.

Mobile 1 Smobile 1 just get a couple of quarts of Synlube!

Redline SuperLight Gear Oil - a 70W/75W GL-5 gear oil with the viscosity of an ATF. This is used when temperatures are not high and when the maximum power output is required such as in qualifying laps.

Maximum power output would be when you have minimum friction loss

Its GL-5. Never tried it myself.

How long does it take Synlube to get back to you? I emailed them over a week ago and still no reply so far.

Sometimes he gets too many emails and busy with manufacturing and shipping product. You might try giving him a call.

800-SYN-LUBE
702-683-8292

Mailing Address:
2961 Industrial Road #300
Las Vegas, NV 89109-1134

Ok I should ask, what is the difference between GL4 and GL5, and which is Mobil 1 gear oil?

https://www.pennzoil.com/products/gea..._gear7590.html

Pennzoil® Synthetic Gear Oils 75W-90
GL-4 and GL-5

Available in SAE 75W-90 viscosity grades of either API GL-4 or API GL-5 service classifications. Specially formulated with synthetic base stocks to meet the requirements that today’s cars, minivans, SUVs and light-duty trucks encounter in normal and severe driving conditions.

The synthetic base stocks used in Pennzoil® Synthetic gear lubricants provide better protection than low- and high-temperature conventional mineral-oil base stocks. They offer protection over a wide temperature range.

The API GL-5 product is specially suitable for use in limited slip differentials.

quick explanation of differences in GL4 and GL5. As for my comment about the scions and GL-4, here is an email from scion saying GL4 is better (not mine, from a guy on the scion board).

I used this Red Line MT-90 in my xB's transmission. It made an amazing difference, the transmission feels smoother and engages gears much easier. The Red Line fluid costs a bit more, but it is a high-performance gear oil with great anti-wear properties.

Mobil 1 is a brand of synthetic oils & lubes. It was the first and is still regarded by many as the best synthetic oil/fluids. I haven't used it ever so I have no opinion either way.

I know I added some really old (20 years) Slick50 Gear lube to my xB tranny oil and it increased the mileage and then switched just the tranny oil to Synlube before I did the engine oil and the mileage stayed the same with the Synlube. I have a feeling that the Synlube will result in much longer service life and probably provides more power transfer at heavy loads than the stock gear lube even with the Slick50 add to it.
If you use Red Line oils make sure you get ones made for daily use not racing use as the racing oils are not intended for prolonged use.

GL-5 is for limited slip differentials NOT for transmissions.