GL-1 or 50W motor oil for trans? manual says 80W/90

[ylbill]

ok, I know these two products have been discussed when changing tranny fluid, but has there been a clear winner (GL-1 or 50W motor oil)? I'm about to change mine...do we have a winner?

My manual actual says SAE 80W/90 oil (not EP) with anti-wear additives.

[rlux4]

No, there is no clear winner. This has been discussed probably more than any other single topic and it's still a matter of personal choice. GL-1 is recommended by some of the most knowledgeable people around, and then you have those like Ventura Ace, who is extremely knowledgeable, and uses Valvoline racing oil. He posted a picture of the inside of his tranny and it was a thing of beauty.
I use GL-1. I changed the oil when I first got my car and used 50W. Shortly afterwards the tranny self destructed. It was probably ready to go anyway, but GL-1 was recommended by, and shipped with the tranny by Jon Logan who supplied my rebuilt replacement.
Ron

[RRoller123]

I am NOT an expert by any means, but I will testify that when I used Redline MT-90 in my transmission the change in smoothness was unbelievable. Like a new transmission. I will keep using it.

Pete

[ga.spyder]

Havent we done this before? After seeing Ventura Ace's post and pics of his tranny,I went with the Valvoline 50w racing oil.Hey,the mans a engineer.I have used it for 2 years with no issue.The biggest difference is how smooth the tranny is,especially in cool weather.I know people who have run the synthetic Redline for years also.I think it boils down to personal preference.

[RRoller123]

Like I said, I am no expert, just giving testimony! <{:^)

Pete

[manoa matt]

I default to the engineers who built the car. It's cheaper and more readily available.

[So Cal Mark]

I've talked to chemical engineers from Castrol, Mobil 1 and Royal Purple. They all recommended 40w motor oil

[djape1977]

if it's of any importance, user manual for my 1980 fiat 132 2000 says that manual gearbox should be filled with same oil as the motor, 15w40

[wikkid]

if it's of any importance, user manual for my 1980 fiat 132 2000 says that manual gearbox should be filled with same oil as the motor, 15w40

I'm not sure I would feel safe assuming tech specs for one engine would be the same for another, especially when the Spider manuals call for GL-1.

[djape1977]

it's exactly the same engine as in 124spider 2000. 1995ccm fiat twincam with 112hp.
and i've been running engine oil in several of my cars over the years without any problems. all fiats and derivatives, 124sport, 850sport, 125, 132, lada...

[So Cal Mark]

viscosity is measured differently for gear oil and motor oil, so that 40w motor oil is the same viscosity as 80/90 gear oil

[ylbill]

viscosity is measured differently for gear oil and motor oil, so that 40w motor oil is the same viscosity as 80/90 gear oil

oh, I didn't know that...thanks. Since I already have a quart of Lucas SAE 80W-90 gear oil -Trans & Diff Lube, I guess I'll just pick up another quart of that. Thanks

[manoa matt]

"I already have a quart of Lucas SAE 80W-90 gear oil -Trans & Diff Lube"
This is most likely a EP (Extreme Pressure) oil with "anti-wear" additives. It will eat up the brass syncro rings.

[ylbill]

"I already have a quart of Lucas SAE 80W-90 gear oil -Trans & Diff Lube"
This is most likely a EP (Extreme Pressure) oil with "anti-wear" additives. It will eat up the brass syncro rings.

Thanks Matt, I guess I'll pass on using that. I guess I'm back to my preference...40W or GL-1?

[manoa matt]

1 gallon 90W GL-1 Napa part # 65-201 = $14 Enough for more than two trans fluid changes, thats about $7 per fluid change. Most gear oils are $7 for one liter and you need two, so the GL-1 is a very economical solution. It just makes sense. Regular 40W or 50W motor oils may* be cheaper per quart than GL-1 but could* contain "cleaning agents" "anti-wear additives" or other unknown chemicals not specifid on the bottle. Considering the cost of the syncro rings and a trans rebuild, I'm not taking that chance. I don't have the time to research the exact forumlations of various motor oils.

When you drain the trans there is also a tiny square plug at the very rear passenger side. There is a separate chamber in the back part of the trans. As you fill the trans and the oil level rises it spills over a wall in the trans casting and reaches that back chamber. When you drain the trans through the drain plug located in the bottom trans plate the oil in that back chamber can't get out, hence the secondary plug.