Using 80W-90 oil (instead of 75W-90) for manual transmission?

OP, just curious why you're looking to change weights? Is it coming down to availability or is it performance based?

FYI, I've always used Mobil-1 10W-30 in my AX-15 with good success.
 
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Thanks for the replies guys.

As to why, it's mainly due to 75w 90 not being readily available in gl4. Even if they had it's expensive and comes in 2.5L bottles.

This one comes in a 4L bottle and cheap enough so I thought if it's not harmful why not use this?

Btw is that weight difference big enough?
 
PE is just some code that I put in. I'm in Australia and those redlines are so expensive here.

Do you think using that mineral 80w 90 be an issue due to weigh difference and not being synthetic @Jerry?
 
Dyl said:
PE is just some code that I put in. I'm in Australia and those redlines are so expensive here.

Do you think using that mineral 80w 90 be an issue due to weigh difference and not being synthetic @Jerry?
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Since Australia doesn't get cold I'd run the 80W-90 GL-4 conventional without hesitation.
 
Dyl said:
This is for transmission (not axles).

Anyways thanks Jerry for confirming. :)
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Whoops you're right, kinda lapsed back into that mode when you asked about the conventional vs. synthetic. I usually recommend a synthetic for a transmission but that's so it'll shift better in extremely cold conditions, not likely ever a problem where you drive.
 
Don't run this, as it's for GL5 which means it has the sulfur in it that destroys GL4 transmissions with brass syncros. The only reason they list GL4 in the description is that is covers the lubricity that GL4 requires. If it is compatible with GL5, that means it has the destructive sulfur in it. The fact that it says for hypoid gears sorta says it all.

Can you not just order a jug of redline from Amazon and call it a day?
 
machoheadgames said:
Don't run this, as it's for GL5 which means it has the sulfur in it that destroys GL4 transmissions with brass syncros. The only reason they list GL4 in the description is that is covers the lubricity that GL4 requires. If it is compatible with GL5, that means it has the destructive sulfur in it. The fact that it says for hypoid gears sorta says it all.

Can you not just order a jug of redline from Amazon and call it a day?
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Penrite does an aussie top shelf oil that many here use and its good for Brass synchro's , cant remember which one but its readily available in all Auto shops unlike the MTL which is close to $100au for 2 quarts delivered or big mark up at race shops.
 
Fishtaco said:
Penrite does an aussie top shelf oil that many here use and its good for Brass synchro's , cant remember which one but its readily available in all Auto shops unlike the MTL which is close to $100au for 2 quarts delivered or big mark up at race shops.
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That’s fine, I just wanted to make the point that the Castrol he asked about is not safe for his transmission despite other telling him it’s safe and the website saying “GL4”. He should look into the one you mentioned, or Redline, or similar. The stuff he linked is the same shit that was wrong in the owner’s manual that nobody should be running.
 
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machoheadgames said:
That’s fine, I just wanted to make the point that the Castrol he asked about is not safe for his transmission despite other telling him it’s safe and the website saying “GL4”.
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Precisely what is it about that particular lube makes it unsafe for his transmission?

A GL-4 rating is exactly what our manual transmissions prefer. Or a GL-5 with the GL-4 compatibility that means it does not include the sulfur based additives that make a pure GL-5 unsafe for the yellow metal synchronizers in a manual transmission?
 
Jerry Bransford said:
Whoops you're right, kinda lapsed back into that mode when you asked about the conventional vs. synthetic. I usually recommend a synthetic for a transmission but that's so it'll shift better in extremely cold conditions, not likely ever a problem where you drive.
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Jerry - I can’t believe that I was here to witness your first mistake. You are human after all….

;)
 
Jerry Bransford said:
Precisely what is it about that particular lube makes it unsafe for his transmission?

A GL-4 rating is exactly what our manual transmissions prefer. Or a GL-5 with the GL-4 compatibility that means it does not include the sulfur based additives that make a pure GL-5 unsafe for the yellow metal synchronizers in a manual transmission?
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Well there aren't a ton of details to go off of in the product description so you mostly have to make assumptions, but it does not state safe for yellow metals specifically. There are oils around that claim dual compatibility (GL4/GL5), that are in fact not safe for yellow metals due to their sulfur content, so it would at least be wise to confirm this is not one of those before choosing it. They're pretty vague in general in the description so it might be smart for him to call Castrol or something before buying it. I dunno, but I certainly wouldn't buy it simply because of the GL4 in the description without at least a confirmation that it is yellow metal safe.

If I were in that situation I would likely buy the one fishtaco mentioned since it seems to be a safe bet and is locally available over there for a more reasonable price.
 
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