Regular Tranny Grease vs Sythetic Grease

[Keith]

I have a 97 GEO METRO 3 cyl manual tranny with 160,000 miles on it. I don't know what type of tranny grease is presently in it and need to add 1 qt. to fill it up. Is it ok to mix the 2 types of grease and what type should it have in it?

[MetroMPG]

I'd do a full flush and put in GM Synchomesh or equivalent.

See this thread for more info:
Synchromesh GM Part Number

[dieselescort]

You should not mix and match because synthetic when combined with standard oils will cause foaming. Most likely it's standard petroleum oil unless it seems like the previous owner was into performance mods...which with a Metro is probably not the case!

[Christ]

From AMSOIL:

Myth #4: Synthetic lubricants are not compatible with petroleum.

Untrue. The synthesized hydrocarbons, polyalphaolefins, diesters and other materials that form the base stocks of high quality name brand synthetics are fully compatible with petroleum oils. In the old days, some companies used untested ingredients that were not compatible, causing quality synlubes to suffer a bum rap. Fortunately, those days are long gone.

Compatibility is something to keep in mind, however, whether using petroleum oils or synthetics. It is usually best to use the same oil for topping off that you have been running in the engine. That is, it is preferable to not mix your oils, even if it is Valvoline or Quaker State you are using. The reason is this: the functions of additives blended for specific characteristics can be offset when oils with different additive packages are put together. For optimal performance, it is better to use the same oil throughout.

If the Foaming thing were true, we wouldn't have part-syn oils on the market. Think about it.

[Frank Lee]

The "grease" in the title threw me off a bit...

however many riding lawnmowers and similar equipment use grease in the trans, not oil. I wasn't expecting that the first time I came across it.

[Christ]

Originally Posted by Frank Lee

The "grease" in the title threw me off a bit...

however many riding lawnmowers and similar equipment use grease in the trans, not oil. I wasn't expecting that the first time I came across it.

Yeah, some jackass pumped the rear end of one of my tractors full of grease... medium duty garden tractor (Gilson 12HP), it was leaking oil out the transaxle case, so instead of sealing it up properly, he drilled a hole, put in a Zerk fitting, and pumped 'er full of blue grease. Dumbass. He pulled a trailer with it, and popped the case open from the heat buildup and pressure that the grease couldn't dissipate like oil would. I got that tractor for like $40 with a good 12HP Tecumseh motor.