Is Dexron III/Mercon ok?

[Stan Simpson]

Changing the hydraulic filter (power steering/cooling system) and the owner's manual says to use Dexron III. Googling it always shows Dexron III/Mercon? My research shows that Dexron III is no longer licensed by GM. There are many house brands that claim to be Dex/M or DexIII/Merc6, etc.

Can anyone advise which is the correct one?

Also, should I fill the new filter with fluid before installing, like I do with the fuel and oil filters?

Thanks.

[Mike Shumack]

Dexron III (or its equivalent) seems to be widely available. It was said on the irv2 forum (Allison Transmission thread) that Transynd is an alternative for Dexron III (it's a superior product but twice the cost of Dexron III). I would just use the Dexron III.

I have not changed my hyd fluid yet (it's on my to-do list) but from what I read (for my coach setup) the filter is mounted below the hyd tank and when the filter is removed it will gravity drain the tank. So if your filter is mounted low too, you don't need to prefill it.

[Stan Simpson]

the filter is mounted below the hyd tank and when the filter is removed it will gravity drain the tank. So if your filter is mounted low too, you don't need to prefill it.

I'm worried about this comment. The owner's manual says the hydraulic reservoir holds 48 quarts. Are you suggesting that I will have 48 qts of transmission fluid coming out? I only have a couple of empty 5 gallon buckets, and they would only hold 40 qts. I'll be poised to put the new filter on immediately, but I have to clean the mounting base first, so it won't be that quick.

I looked at the reservoir, and it sure doesn't look to me like it could hold that much, but I suppose most of the fluid is in the lines, and they go all the way to the power steering.

[Mike Shumack]

When I do mine, I plan to pump as much out of the tank as I can before removing the filter. Just to keep things as clean as possible.
I carry a fluid transfer pump (hand operated) - and you can get one at most auto parts stores. I already used it to pump 48 qts from my engine drain pan back into the old gallon containers for disposal, and same when I did the transmission oil change. I works well and provides a little bit of a workout too.
I have this pump https://www.amazon.com/Koehler-Enterprises-RA990-Multi-Use-Transfer/dp/B0181EDCZ6/ref=sr_1_3?ie=UTF8&qid=1530569541&sr=8-3&keywords=oil+transfer+pump

[Dave Atherton]

Stan, I would suggest to pre fill the hydraulic filter with a good quality non-foaming Hydraulic
Oil. The reason with some hydraulic pumps pushing a column of air can hang up movement of
hydraulic valve spools and can damage hydraulic pump because hyd fluid cannot pass hydraulic
fluid return back to hydraulic tank. Some units have gear type hydraulic pumps or piston pumps
which are called positive displacement pumps which require anytime hydraulic fluid is drained from pump, the hydraulic pump has to be bleed on air by loosening pressure line fitting at hydraulic pump
cranking engine over but not starting. When good flow of fluid is seen than tighten hydraulic fitting
at pump than your safe to startup. Dave Atherton Retired Cat Mechanic