Re: Oil pressure and mult-viscosity oil.

Posted by Fish'n Jim on 2019/11/11 10:53:15
When you change oil service, you change not just viscosity profile, but additive package. T-4 is made for DIESEL applications, which have much more pressure, soot, and combustion products to contend with. Those additives can loosen some of the accumulated engine sludge from gasoline.
Personally, I do not like to change oil if the engine has not been rebuilt where you're starting with clean surfaces and passages, no sludge. And rarely would I just take someone's word for adding something without investigating. Can not go by sound alone, either.
These motors don't have the full pressure filter lubrication we're used to today, mostly partial drip filters, if at all. eg; My '49 has no oil filter.
Also, you're only seeing the oil pressure gauge reading, not the actual oil pressure, per se. If it's a mechanical gauge maybe some sludge got in the tube. If sludge gets in the pump intake, it could drop the pressure momentarily too, til it clears out.
If it's electric gauge, maybe the pressure was fine and voltage* dropped and/or the regulator was stuck. Contacts systems are a little bit more unreliable than electronic we're used to today. Plus they're that much older now than new.
My recommendation; do an oil change, ASAP, and maybe several more, if you keep using this oil, til it clears up. I think the manual calls for a periodic pan drop and scrape on some of these with no filter. But maybe not necessary, but can't know the extent without checking.
* - won't take much on a 6V system.

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