Thread: OT understanding an old engine spec plate

A 20s truck engine at the Laidley Pioneer Village has the following data plate re its oil requirements. Its American so the degrees of which it speaks will be fahrenheit.

"Caution. Use an oil of not less than than 80 viscosity at 210 degrees and minimum flash point of 420 degrees"

Does anyone know what this translates to in modern oil speak? Does 80 viscosity in the 1920s still mean 80 viscosity as we would understand it today?

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I can't remember ever seeing engine oil that thick, not even the total loss oil systems.
You could give castrol a call they are quite helpful.
Here is their classic oils https://www.castrol.com/en_gb/united...gine-oils.html
and penrite here https://www.penriteoil.com.au/applic...tage-classic#/

I had a 1947 air cooled V twin HD. I had a 1970's vtwin prior to that and the specs said to use a straight 50W oil but that just turned to water in todays traffic and I burnt out the valves guides waiting at a road works traffic jam. I found this https://www.penriteoil.com.au/produc...0-70-mineral#/ which will string if you take your finger out of it at room temperature. That was actually 25 years ago and I was in the UK. This Australian product was the only thing addressing the problem, that I could find. It was quite expensive to get in UK but here its relatively cheap. It has kept that '47 engine in great condition and the oil pressure always registered a few PSI even when hot.

The bike was all roller bearings, (no plain bearings) so the oil pressure was low. Being air cooled, the temperature could get very high. When I first saw that oil, I thought there's no way you could put that in an engine because its too thick, but it saved the day when the bike was stopped with no air cooling. Sometimes there's no avoiding it in UK traffic. I would guess the HD oil would meet the specs of your old engine but anyway Penrite might be another company to ask advice.

I used nothing else than W-40 in my 38 norton ES2 and 1958 Matchless G80S, both roller bearing machines. Still ride the 58 Matchless, haven't touched the engine since I totally restored the bike in 1989. Lucas or Pennzoil have the 0-40 oil.

It's hard to get definitive information about engine oil.
Maybe you could post a query here:
Bob Is The Oil Guy | The Internet's Number One Motor Oil Site

My first thought was that it's measuring in Engler, but 80 Engler is waaaay too thick for an engine, so with much Googling, I think I have something...

"For single non-winter grade oils, the kinematic viscosity is measured at a temperature of 100 °C (212 °F) in units of mm2/s (millimeter squared per second) or the equivalent older non-SI units, centistokes (abbreviated cSt)" (Wikipedia)

So, it's probably 80 cSt, which converts to 430 Saybolt Universal (SSU) (Viscosity Tables), which converts to about 30 SAE (Viscosity conversion table), which is pretty reasonable for an engine.