Correct oil/atf/other liquids for 340-2 / ST300 etc?


I'm looking for the "modern equivalents" of the liquids mentioned in my 1967 Owners Manual, to give my LeSabre Coupe a nice service.

Engine oil (340-2):
"SAE 10W-30 up to 5W-20, depending on lowest anticipated (outside) temperture". - What are you using? Is selecting a good 5W-30 fully synthetic oil a good idea or do you rather chose a "special vintage car" mineral oil instead?

"GM Spec. 1899-M" - Right now the system is filled with a translucent "neon green" coolant. Any idea what this might be?

Power steering:
"Buick power steering gear fluid"...whats the best modern replacement?

ATF (ST300):
"Special Buick Transmission oil or AQ-ATF"...what to get these days?

Real axle/diff:
"SAE 80 or 90 multipurpose gear lube, GM Part No. 1050081"...can you just use a 80W-90 (GL5) oil here?

Thanks for any advice!

I like to use oil that is engineered for flat tappet motors. It has the correct balance of ZDDP and detergents.

Everything else is backwards compatible.
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Hi Todd Larry,

thanks for the info - could you please suggest a specific brand/oil?

Ah, please ignore already did that...sorry.

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Engine oil: As Larry linked to Joe Gibbs oil is considered one of the best, although for average usage, I would say any reasonable "hot rod" oil will do just fine, or you can do as I do and run 15-40 diesel engine oil (it's readily available to me and I like the high detergent aspect to it). While a fairly common practice it has it critics, and even diesel engine oil is loosing it's zinc.

Coolant: Here again, there have been many changes, I still run diesel engine coolant in all cast iron engines, recommending aluminum compatible for engines with aluminum heads, and/or blocks. Aluminum radiators I don't see as a problem as they are not exposed to the heat.

Power steering: Any hydraulic oil is suitable, most just use their transmission fluid. A transmission fluid suitable for Dextron III is common.

ATF (ST300):
Dextron III compatibility is what I look for in a GM compatible transmission oil

Real axle/diff: Any 80-90 gear oil is good in the rear unless it is a posi, then it needs either posi compatible or an additive.

Caution, my opinions are subject to criticism.

thanks heaps for this bunch of info!

Unfortunately that "Joe Gibbs Oil" seems not to be easily available over here and Oil in general is not stating its zinc content/level on the bottle or the product description.

So it comes down to some user generated lists of different oil brands/types with (supposed) higher zinc level. I'll try to get one of those.


thankyou, but this stuff isn't directly available over here it seems - and if I order it in the U.S., shipping costs will exceed the product price.

But I found two alternatives:

1. Edelbrock Zinc Additive
2. COMP Cam Engine Break-In Additive

Both seem to be similarly priced and effective and will treat 6 quarts/liters.
Does anyone know which one to maybe prefer?

Harry, The Comp product is designed for engine break-in and not necessarily regular use after that. The Edelbrock seems similar to the ZDDP suggested earlier.