FL5 Transmission Fluid recommendation

[PointByPatrol]

Really good information over there. Good write up. I do track my car so thats why I went with the motul 75w-90, but after reading that I may just go to the fluid Ben recommended

I haven't had any issues with the AC Delco fluid. No metal coming out of the transmission either when exchanging the fluid. I've been pleased with it.

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[mattrose4]

I haven't had any issues with the AC Delco fluid. No metal coming out of the transmission either when exchanging the fluid. I've been pleased with it.

I might do another fluid swap before race season starts up. Motul 75w-90 might be a little much and since I live in the midwest it gets cold out here too.

 

[Spart]

Really good information over there. Good write up. I do track my car so thats why I went with the motul 75w-90, but after reading that I may just go to the fluid Ben recommended

If you are tracking your car, Motul 75W-90 is probably a great option. I can't specifically speak to it and I included it in my list of suitable fluids.


One thing about the Motul product is that it's claimed to be suitable for both GL-4 and GL-5 gear oil applications. That's not to say it's worse, but compromises must be made somewhere. The reason you typically don't want to run a GL-5 gear oil in a manual transmission is this:

Yes, don't consider a GL-5 in any weight for this or nearly any other manual transmission. They usually contain sulfur-phosphorus extreme pressure (EP) additive, which is great for a hypoid gear in a ring/pinion differential. Our cars on the other hand, being FWD only, do not have hypoid gears in the diff and thus have no need for the EP additive. Additionally (and most concerningly) that additive is corrosive to the yellow metals in your synchros, and possibly also shift forks, bushings, and thrust bearings depending on the particular trans.

GL-5 is what I put in the front and rear diffs of my Tacoma. The gearbox gets a separate GL-4 fluid, even though it's similar in viscosity to the diff fluid and I could save a few bucks by consolidating consumables.

I like Redline MT-90 because it's specifically a GL-4 for manual transmissions only, and is not applicable as a gear oil for hypoid differentials.

Amsoil 75W-90 Manual Transmission & Transaxle Gear Lube (note that this is NOT the same as their "Severe Gear" GL-5 product) is also strictly a GL-4 for manual transmissions.

I'm not sure what the engineered use case is for the Motul - perhaps it's for transverse-mid-engine layouts where you have a transaxle and a hypoid gear sharing fluid? I'm not sure what the motivation is for a product that's both GL-4 and GL-5.

Regardless, Motul makes great fluids, I'm just not sure if it's the best option in 75W-90 manual transmission fluid here.

 

[Spart]

I might do another fluid swap before race season starts up. Motul 75w-90 might be a little much and since I live in the midwest it gets cold out here too.

If it feels like it shifts fine when cold (whatever cold means where you are) then I wouldn't worry that much about it.

Our transmissions do have a pump, and one thing that you have to be aware of with cold temps and thick fluid is cavitation in gerotor pumps.

If it was really an issue, you'd think we'd hear about people with broken pumps by now. But then again, how many people are switching to 75W-90 and beating on their cars in extreme cold? Probably not many.

"Just keep the revs down and drive gently until the car warms up" remains good advice as always.

 

[mattrose4]

If you are tracking your car, Motul 75W-90 is probably a great option. I can't specifically speak to it and I included it in my list of suitable fluids.


One thing about the Motul product is that it's claimed to be suitable for both GL-4 and GL-5 gear oil applications. That's not to say it's worse, but compromises must be made somewhere. The reason you typically don't want to run a GL-5 gear oil in a manual transmission is this:



I like Redline MT-90 because it's specifically a GL-4 for manual transmissions only, and is not applicable as a gear oil for hypoid differentials.

Amsoil 75W-90 Manual Transmission & Transaxle Gear Lube (note that this is NOT the same as their "Severe Gear" GL-5 product) is also strictly a GL-4 for manual transmissions.

I'm not sure what the engineered use case is for the Motul - perhaps it's for transverse-mid-engine layouts where you have a transaxle and a hypoid gear sharing fluid? I'm not sure what the motivation is for a product that's both GL-4 and GL-5.

Regardless, Motul makes great fluids, I'm just not sure if it's the best option in 75W-90 manual transmission fluid here.

Well said! The only reason I went with it, is because that's what I run in my track STI that I race. The 2 have very different transmissions, but it was a fluid I know works and Im confident in running. I think I may do a fluid swap to AC delco fluid that ben was recommending. I live in NWI Indiana and we do get cold weather up here and I noticed a light transmission hum on a cold start when the weather is under 20 degrees and its been sitting for a couple days. Im assuming due to the fluid being a little too thick. It goes away when the car run for 2-5 minutes. Seems like 75w-90 might be a little thick for the cold.

 

[mattrose4]

If it feels like it shifts fine when cold (whatever cold means where you are) then I wouldn't worry that much about it.

Our transmissions do have a pump, and one thing that you have to be aware of with cold temps and thick fluid is cavitation in gerotor pumps.

If it was really an issue, you'd think we'd hear about people with broken pumps by now. But then again, how many people are switching to 75W-90 and beating on their cars in extreme cold? Probably not many.

"Just keep the revs down and drive gently until the car warms up" remains good advice as always.

Comfort mode, low revs, during the cold seasons always. I dont beat on the car till its race day tbh. I always let the car run for 5 min before I drive it

 

[Spart]

Comfort mode, low revs, during the cold seasons always. I dont beat on the car till its race day tbh. I always let the car run for 5 min before I drive it

One nice thing about these cars (until it isn't and you're overheating) is that the transmission "cooler" is actually a heat exchanger that works with the engine coolant. So idling the car warms both, whereas ordinarily you'd need to actually drive a manual car a good distance in order to warm the transmission fluid up.

 

[Jack90210]

So I remember a very long time ago I used to use redline oil. I had a 91 Civic with a manual transmission. And I put the red line transmission fluid in it. All I remember was the transmission having to be replaced because it was shredded. And I didn’t drive that car hard. After that, I never use red line again.

Like most manual gearboxes, those transmissions take gear oil, not ATF -- just to be clear.

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