1985 4sp manual T19 (Ford F250) Mixing fluid okay?

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I'm still trying to wrap my head around the appropriate oil type for this transmission. Vehicle is a 1985 Ford F-250 4x4 w/ 4 speed manual. Unit is a Borg Warner T19. Owners manual suggests straight 50 weight motor oil, or GL-4 80W-90 gear lube. Straight 50 weight is proving impossible to find, and 80w-90 gear oil is almost always of the GL-5 type which I've heard/read is corrosive to the yellow metals used in the synchros. Based on my experience trying different oils, the transmission is sensitive to oil weight in cold weather. When I first bought the truck, I used Pennzoil Synchromesh, whose viscosity as I understand it, is on the thin side; probably closer to ATF than 80w-90 gear oil. This oil was GREAT in cold weather, but I was unsure of compatibility with this tranny, so I drained it and tried SAE 90 GL-4 manual transmission lube. The 90 weight is miserable in cold-- if it's below 15F in the morning, I can hear the bearings in the tranny, and the engine RPM of a cold idle (high idle during warmup) drops about 200 RPM just turning the tranny internals until the fluid begins to circulate / warm up sufficiently. I'm at a loss as to what I can use for good performance in cold weather. With the 90 weight lube, shifting in cold (below freezing, without a 10-15 minute warm-up) is like trying to drag a spoon through frozen molasses. With the Synchromesh, it was effortless at any temp. But when I drained the Synchromesh, I thought I saw a silver sheen to the drain oil, indicating that there's a lot of extra wear metal, leading me to believe it's not the proper lube for this application. Any input, suggestions, info, tips, experiences, etc. would be much appreciated!
 

92saturnsl2

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Originally Posted By: artificialist
Many companies make a synthetic 75w90 GL-4 oil, maybe that would solve the problem?
Trying to find a product locally. Amsoil is stupid expensive when shipping is factored in; I can nearly buy a replacement junkyard transmission for this truck for what a case of the synthetic 75w-90 MTF would cost me. My other thought was to mix some ATF / MMO or something in with my SAE90 gear oil. I wonder how that would work out....
 
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Originally Posted By: 92saturnsl2
Originally Posted By: artificialist
Many companies make a synthetic 75w90 GL-4 oil, maybe that would solve the problem?
Trying to find a product locally. Amsoil is stupid expensive when shipping is factored in
NAPA always has it in stock around here.
 
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That is a reliable indestructible well built trans so treat her good. GL4 80w-90 gear lubes are fine...better yet that Amsoil GL-4 or Redline someone mentioned here would be excellent.
 
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I put redline MT90 in mine. Was available locally in this 2 horse town. Napa should have SAE 50 in Valvoline or Napa brand. Every parts store will have Valvoline racing SAE 50 on the shelf. My last truck got SAE40 in it's t19.
 

cos

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Amazon.com has Redline MT-90 (75W90) for $15.29/qt and free shipping. You'll probably need 4 qts.
 
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Originally Posted By: Chris142
I put redline MT90 in mine. Was available locally in this 2 horse town. Napa should have SAE 50 in Valvoline or Napa brand. Every parts store will have Valvoline racing SAE 50 on the shelf. My last truck got SAE40 in it's t19.
Yeah, I've seen SAE50 in recent years. But if all else fails, the OP can try a Harley Davidson dealer, they should still have some SAE50 I think...
 
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Any heavy duty truck shop should be able to fix you up with SAE 50 - it was the standard spec for Fuller transmissions for years. Fuller is the most popular manual gearbox in Class 8 trucks. You may have to bring your own container - its usually in 120 lb. kegs.
 
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SAE50 isn't a multiweight. Even a full synth wouldn't be cold friendly. A 75w90 GL4 from Ford, Redline, Amsoil... is your best bet. A 75w85 GL4 from GM, Mopar, Nissan, Hyundai... is another option for a non-worked stock powered truck.
 
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My uncle uses SAE50 oil...he got it from a truck stop, I think it's made by Chevron. My T19 got 75W-90 gear oil, I recall from NAPA.
 

92saturnsl2

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I ended up finding Valvoline Racing SAE50 motor oil at Autozone for a reasonable 5 or 6 bucks per quart. Took 3.5 quarts. Interestingly enough, straight SAE50 should be equivalent to a thick SAE90 gear oil according to viscosity charts I've found online. However the cold weather performance is markedly improved over the SAE90 GL-4 gear oil I switched out in favor of the Valvoline. The shifts still feel a little stiff/rubbery when it's down to 10F or lower (till it warms up), but huge improvement nonetheless. No noise from the transmission when cold can only be a good thing smile
 
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