AMSOIL ——› Differential fluid
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Pro
Joined: Apr 2011
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From: Canada
AMSOIL ——› Differential fluid
Guys, I am going to have a mechanic change the differential fluid in my '89 vette and I don't want to make a mistake bringing him the wrong fluid. I am thinking about trying AMSOIL. I read that the factory fluid from GM is 80W-90 oil with a slip additive in an 1989. I also read AMSOIL sells a 75W-90 and 80W-90. I just want to know what AMSOIL oil should I use for the rear differential and I plan on adding one bottle of limited slip additive. Can I add a limited slip additive from another brand other than AMSOIL ? Would love to hear any advice from anyone with experience using AMSOIL in their C4's differential fluid. Thank you. (UPDATE: I made a decision in post #19. Thank you.).
Last edited by ~ Anno Domini; Aug 14, 2019 at 03:45 PM.
Burning Brakes
Joined: Jan 2005
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From: Shelby Township Michigan
I run it in all my cars and have never had any issues. High horsepower Caddy and a C6 Vette I recently sold and they were both boosted with drag radials on them 24/7 and I never had an issue. The C6 Vette did have a built rearend but all my past cars have never had an issue with it.
Team Owner
Joined: Jul 2004
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From: Hartford WI
That is what I have done forever. That is until I was getting a dyno tune several years ago and did a "while you are there" service on the rear end and they gave me the remainder of the bottle of blue stuff. Think that is Redline and they said they didn't use additive for this oil?
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From: Canada
Thank you for all your advice, guys. Mr. Peabody, what you have done is what I was thinking about doing, that is, to use AMSOIL, but put in a bottle of the GM additive first. Do you have the AMSOIL product link you used like 75W-90 and 80W-90 ? I don't know what AMSOIL oil weight to use. Thank you.
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Go with the 75W-90 Severe Gear oil. It already has the additive in it and you do not need any more. Back when my car was a street car I ran it without the additive and never had an issue.
https://www.amsoil.com/shop/by-produ...-EA?zo=1934716
https://www.amsoil.com/shop/by-produ...-EA?zo=1934716
Advanced
Joined: Jan 2019
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I know it's probably a different differential than yours, but I recently had the fluid changed in my 96. I took the shop the amsoil 75w/90 and explained it shouldn't need any additional friction modifier... but they wanted to use one anyway. Rather than wait and order the amsoil additive, I just had them add the GM. It's only been 6 or 8 hundred miles since, but i've had zero issue with that combo so far.
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Pro
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From: Canada
Thanks for the helpful info fellas, could anyone explain the difference between AMSOIL 75W-90 and 80W-90 at the link below ? If my 1989 takes 80W-90 from the factory, would the 80W-90 be more appropriate than 75W-90. Thank you.
https://www.amsoil.com/shop/by-produ...?code=AGLPK-EA
https://www.amsoil.com/shop/by-produ...?code=AGLPK-EA
Melting Slicks
Joined: Dec 2004
Posts: 2,655
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From: Dallas TX
IMO, in these cars, there is no real functional difference between 75w90 and 80w90... IMO.
The 80w90 is a newer(not sure what year) Amsoil fluid. The 75w90 version has been around forever.
I dont think you can go wrong with either, but I can guarantee there are a lot more people running 75w90 Severe Gear in their cars than the 80w90.
The 80w90 is a newer(not sure what year) Amsoil fluid. The 75w90 version has been around forever.
I dont think you can go wrong with either, but I can guarantee there are a lot more people running 75w90 Severe Gear in their cars than the 80w90.
Le Mans Master
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From: Everett WA
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That is what I have done forever. That is until I was getting a dyno tune several years ago and did a "while you are there" service on the rear end and they gave me the remainder of the bottle of blue stuff. Think that is Redline and they said they didn't use additive for this oil?
Drove back to the shop, put the additive in. Drove home did the three 90 degree turns with no issues. So when we changed it at 80K and again at 130K we just put the additive in prior to the Amsoil. I'm not a chemist nor and engineer .. but I drive my car a lot and know when it feels like it's working properly. This works for me. YMMV
Le Mans Master
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Thanks for the helpful info fellas, could anyone explain the difference between AMSOIL 75W-90 and 80W-90 at the link below ? If my 1989 takes 80W-90 from the factory, would the 80W-90 be more appropriate than 75W-90. Thank you.
https://www.amsoil.com/shop/by-produ...?code=AGLPK-EA
https://www.amsoil.com/shop/by-produ...?code=AGLPK-EA
Thread Starter
Pro
Joined: Apr 2011
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From: Canada
Guys, quick update on my search for a differential oil. I have Amsoil fluid in my transmission and like it and that's why I want to try it in my differential, but some are saying to use a non-synthetic fluid in the 1989 differential with the GM slip additive. I'll be honest, I need to do more reading before making a decision. I will keep you updated.
Melting Slicks
Joined: May 2013
Posts: 2,692
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From: Sacramento California
I use the 75w90 Severe Gear plus a half-dose of slip lock additive (half dose because the fluid already has some). Normal street driving, no issues.
Practically speaking, there is no difference between the 75w90 and 80w90 fluids.
Practically speaking, there is no difference between the 75w90 and 80w90 fluids.
Safety Car
Joined: May 2001
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From: Fairfax Virginia
I have a 1988 C4 and I have synthetic Mobil 1 with the GM additive and all works great.
Before rebuilding my C3 differential I had that constant clicking on tight turns, After fresh fluid and the additive from GM it was quiet again. I am using Mobil 1 gear oils in both differentials and it works great and does not leak like some told me to expect with synthetic based oils. I think it was 75W90 that I used but it has been a while since I touched either differential.
Best regards,
Chris
Before rebuilding my C3 differential I had that constant clicking on tight turns, After fresh fluid and the additive from GM it was quiet again. I am using Mobil 1 gear oils in both differentials and it works great and does not leak like some told me to expect with synthetic based oils. I think it was 75W90 that I used but it has been a while since I touched either differential.
Best regards,
Chris
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From: Canada
UPDATE: Guys, I like Amsoil and have it in my transmission and I am thinking about using it for my power steering fluid as well, but I ended up putting in conventional, non-synthetic Mobil 1, 80W/90 GL5 gear oil with the GM limited slip additive part number 992694. I went to a local GM dealer and bought one 4 ounce bottle of the slip additiveI for $10.58 Canadian. Then drove a few miles to a Mr. Lube where I knew one of the guys there also had a C4. He changed the differential fluid and put in the GM additive. Mr. Lube provided the conventional Mobil 1 fluid. It cost $89 dollars + $10.58 for the additive. The car drives fine. Thank you all for your help.
Melting Slicks
Joined: May 2013
Posts: 2,692
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From: Sacramento California
Thanks for the update! Glad things are running smoothly. Synthetic oil is not required for these differentials so you will be fine.
By the way, all "Mobil 1" products are synthetic. This is probably what you got:
By the way, all "Mobil 1" products are synthetic. This is probably what you got: