I have taken the mast off and pump off a very old Raymond 20R30TN and mounded them permanently as a lift. I have also added a back-up pump (cheap Chinese unit off a two post car lift... will run anything from Dexron III to N46).

I am only going to use this unit only a few times a day. Pump will run for about a minute each time. The unit is inside so say min. temp. 50 deg F and max 90 deg F (we actually had three days here in VT went over 90).

The original oil also heated up not just because of the lift pump but because the power steering pump shared the same oil sump.

Original rating was 3000 lbs... I honestly can't see putting more than 1000 on it ever.

I am planning on using synthetic oil (I use synthetic in all my machines and vehicles).... most economical seems to be Royal Purple Syndraulic.

I am having a problem deciding on the viscosity.

The original unit used "Texaco Rando HD-B" (from factory tag on original unit). This is a 46 oil.

I was about to purchase the same weight oil.

This made sense to me since this is the manufacturers recommendation and the pump is 30 years oil and might have some wear so 46 might work well.

Then I looked at the viscosity charts and reading articles on hydraulic oil (probably way overthinking this entire subject... but that is a fault of engineers).

Even thought 46 can be used down to 24 deg F it is out of the recommended cST range of 12 to 100 (from an article I read). It will be 100 at 77 Deg F.

If I drop it down to a 32 viscosity then The cSt will be 100 at about 60 deg F.

My only worry this with the old pump (and cylinder), will there be a problem with a slightly thinner oil? Or maybe it will actually protect better since it will be a little thinner at start-up.

I have called or e-mailed several oil manufactures tech lines and all just put it back on me. All can give me their oil specifications but none will recommend what to use in a piece of equipment ( and I understand why... liability).

Can anyone give me some practical advice on what viscosity oil I should use... 46 or 32.

Thanks so much..... Mike