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Gearbox oil
Posted: Fri Nov 07, 2025 5:18 pm
by blade7
It's time to change the gearbox oil in my 91 turbo again. It's been a while, so searched to see what people are using now. And found a post from someone that's a member on here recommending Castrol 75w/140 for road use. So any one have any thoughts for or against?
Re: Gearbox oil
Posted: Fri Nov 07, 2025 5:49 pm
by BennSport
I don’t know anything about the castrol oil, but a lot of people recommend redline MT90. I did a fluid change in my car with it recently and I’ve been happy with how it performs
Re: Gearbox oil
Posted: Sat Nov 08, 2025 2:17 am
by blade7
Poorsche44 wrote: Fri Nov 07, 2025 5:49 pm
I don’t know anything about the castrol oil, but a lot of people recommend redline MT90. I did a fluid change in my car with it recently and I’ve been happy with how it performs
A couple of gearbox guys were very anti about the redline on another forum. It's more the 140 part of the viscosity than the brand I'm curious about.
Re: Gearbox oil
Posted: Sat Nov 08, 2025 6:09 am
by Wespa
Redline MT-90 has been great for me for the past 60 000 miles (with a change in between obviously). I'm in a colder climate, things might be different in racing conditions in warmer climates.
BTW if the car has the stock limited slip differential a mix of two different oils is mandated.
Re: Gearbox oil
Posted: Sat Nov 08, 2025 7:12 am
by gb951
A post from Kevin Gross on r.e.n.n.l.i.s.t.... He rebuilds transaxles for racers and has done a bunch of teardowns, so pay attention.....
To address the original question, the fluids I recommend to my customers are:
Mobil 1 Syn Gear Lube 75W-90
Motul Gear 300 75W-90
Porsche part number 000-043-305-05 (or supersession)
Lubrication Engineers 9919 Monolec Syn
These are all fine choices. There are other GL5 fluids out there which I'm sure are fine, but I do not have enough customer experience with them to say yea or nay. I recommend the Lubrication Engineers fluid for race use.
I will not warranty any transmission that runs Red Line or Swepco fluid.
__________________
Kevin
Catellus Engineering
Re: Gearbox oil
Posted: Sat Nov 08, 2025 9:10 am
by Tom
gb951 wrote: Sat Nov 08, 2025 7:12 am
A post from Kevin Gross on r.e.n.n.l.i.s.t.... He rebuilds transaxles for racers and has done a bunch of teardowns, so pay attention.....
To address the original question, the fluids I recommend to my customers are:
Mobil 1 Syn Gear Lube 75W-90
Motul Gear 300 75W-90
Porsche part number 000-043-305-05 (or supersession)
Lubrication Engineers 9919 Monolec Syn
These are all fine choices. There are other GL5 fluids out there which I'm sure are fine, but I do not have enough customer experience with them to say yea or nay. I recommend the Lubrication Engineers fluid for race use.
I will not warranty any transmission that runs Red Line or Swepco fluid.
__________________
Kevin
Catellus Engineering
Hmmm... I just put Swepco 202 into my Kevin Gross-Built transaxle.... I guess I just voided the warranty.
Very curious statement from
@Catellus Engineering about Swepco, given its reputation in the Porsche world... ??
Re: Gearbox oil
Posted: Sat Nov 08, 2025 12:52 pm
by Thom
Motul gear 75W140.
Re: Gearbox oil
Posted: Sat Nov 08, 2025 8:16 pm
by Fejjj951
Tom wrote: Sat Nov 08, 2025 9:10 am
gb951 wrote: Sat Nov 08, 2025 7:12 am
A post from Kevin Gross on r.e.n.n.l.i.s.t.... He rebuilds transaxles for racers and has done a bunch of teardowns, so pay attention.....
To address the original question, the fluids I recommend to my customers are:
Mobil 1 Syn Gear Lube 75W-90
Motul Gear 300 75W-90
Porsche part number 000-043-305-05 (or supersession)
Lubrication Engineers 9919 Monolec Syn
These are all fine choices. There are other GL5 fluids out there which I'm sure are fine, but I do not have enough customer experience with them to say yea or nay. I recommend the Lubrication Engineers fluid for race use.
I will not warranty any transmission that runs Red Line or Swepco fluid.
__________________
Kevin
Catellus Engineering
Hmmm... I just put Swepco 202 into my Kevin Gross-Built transaxle.... I guess I just voided the warranty.
Very curious statement from @Catellus Engineering about Swepco, given its reputation in the Porsche world... ??
Kevin did 1 of mine as well about a year ago. I trust his expertise and knowledge. I am using Mobil 1.
Re: Gearbox oil
Posted: Thu Nov 13, 2025 5:53 pm
by Latitude48
Tom wrote: Sat Nov 08, 2025 9:10 am
gb951 wrote: Sat Nov 08, 2025 7:12 am
A post from Kevin Gross on r.e.n.n.l.i.s.t.... He rebuilds transaxles for racers and has done a bunch of teardowns, so pay attention.....
To address the original question, the fluids I recommend to my customers are:
Mobil 1 Syn Gear Lube 75W-90
Motul Gear 300 75W-90
Porsche part number 000-043-305-05 (or supersession)
Lubrication Engineers 9919 Monolec Syn
These are all fine choices. There are other GL5 fluids out there which I'm sure are fine, but I do not have enough customer experience with them to say yea or nay. I recommend the Lubrication Engineers fluid for race use.
I will not warranty any transmission that runs Red Line or Swepco fluid.
__________________
Kevin
Catellus Engineering
Hmmm... I just put Swepco 202 into my Kevin Gross-Built transaxle.... I guess I just voided the warranty.
Very curious statement from @Catellus Engineering about Swepco, given its reputation in the Porsche world... ??
Swepco may be fine for use in warm California but in the Seattle area it was awful in the winter as it made shifting very hard until everything warmed up. I don't remember exactly what oil I have in the S2 but I think it's Redline 75W90.