VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc SEA 90 vs SEA 80W-90

Changing transmission lubricant in my '72 Corvette. (4 speed) Is SEA 80W-90 acceptable for use in old transmissions that require SEA-90. I can't seem to find SEA-90 gear oil at my local parts stores. The newer 80W-90 all state recommended for non-synchronized transmissions. Are there any people here who work in the oil industry that would know the answer. I don't want to put the wrong oil in and ruin the synchros.
Steve

You should be able to find it in your area. I checked Advance Auto and they have a Pennzoil #3501 which is listed for syncromesh transmissions. Check the specs with what is listed in the owners manual. The only difference between a straight 90 wt and a 80/90 is the 80/90 will flow a little better in colder weather and still give the same performance as the 90 wt in warmer conditions. The oil will have a classification as a GL# such as GL-4 or GL-5 and that is what you should determine from the owners manual.

Steve is right, and also... I don't think you need to worry about ruining your synchonizers.

An 80W-90 will actually give better lubrication from the start, while maintaining the protection of an SAE 90 when hot.

Regarding GL-4's and GL-5's...
GL-5 is a better lubricant and will maintain the oil film under higher pressures than a GL-4.
I don't know of a single automotive GL-5 oil sold today that will hurt brass/bronze or any other non ferrous parts in a transmission like the original GL-5's of yesteryear would.
That's because the old original GL-5's provided their high pressure protection by actually reacting with and "eating into" the surface of the gear teeth to produce a thin "greasy slimy" film of lubrication capable of withstanding high pressures and the sliding contact characteristics of hypoid gear sets. Modern GL-5 hypoid oils no longer do that... so they won't "eat" brass/bronze bushings or synchronizer rings.

I've had GL-5 oil in all my manual transmissions and rear ends (including 3 ton trucks pulling full loads on soft ground) for decades (same trucks the whole time) with zero trouble.
You MAY notice some increase in effort required to synchronize into gear due to the oil being able to maintain a better film at the synchronizer but it won't hurt anything except maybe your shift time.

I agree with the above.

Thank you all for the advice. I just wasn't sure if the 80W-90 was for newer as well as older transmissions or if it was for 'only' non-synchronized transmissions.
Steve

Hi Steve,

The weight/viscosity ratings of an oil are only part of the decision process. The recommendations you have received will keep things safe.

I suggest that you might want to take a look at some of the specialty oil suppliers for your car. For example, Redline Oils recommends their 75W90NS GL-5 Oil for the transmission in your Corvette. It has a special non-slip additive to help make synchronizers work better. The interesting point is that synchronizers require some friction to make them work properly. Is the oil is too slippery they will not grab well enough to bring the mating gear up to speed quickly.

Royal Purple and Amsoil offer similar oils for manual transmissions.

This is a very interesting thread so thank you to SSG26K (Steve) for posting it and all that contributed. From doing a little research I learned that a Pennzoil product not only has the non-slip additives but is synthetic and made from natural gas. Pretty interesting and amazing how new modern products are developed.

I have straight 90W oil from many, many, years ago. Is it OK to use in my '35?

OK For the winter in cold climates. 140 in the summer. Or 85W-140 all year around if you live in the cold north and drive the car in the winter.

And I agree with the above!
85W-140 is what's in my 29 sedan up here in Saskatchewan.

I agree with Gene and Stovblt above. I also recently discovered that Redline and Amsoil also offer a 75w110. I've always gone with 85w140 but was looking for a solution for a friends weeping pinion on a 4 year old Toyota rear diff that spec'd an 75w90 so I was looking for thicker but not overly thick and the 75w110 looked promising.

With the Vette in particular, I would have a good look at the Corvette, Chevelle, Camaro dedicated forums. Identify your transmission as to whether a Borg Warner, Muncie or other and see what the guys are using. There are very obsessive guys that will try a fluid for a short time, dump it and try another. There are some brands and blends that do indeed work better than others in certain transmissions. I have a Toyota trans in a Pontiac and the forums recommended 2 Redline products together (and Redline approved mixing them). I tried the blend and have been using it for over a decade. The difference in shifting and feel was day and night and I had tried several expensive synthetics but this was just the right spec and brand for this particular transmission and the forums had already done the homework for me...