1Aries

Multi vis vs. oil pressure?

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Recently changed oil to 15/30 syn  blend (Hemmings) from straight 30 in my '34 DRXX;  Pressure is now a little lower at cruise ( 28 psi @ 30 mph)

but quite low at idle.  I'm in favor of the better lubricating quality of syn but worry about the lower oil pressure.  Is the pressure more, less or about equal in importance to the relative lubrication qualities?  Perhaps 15/50w oould have been a better choice??

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Next time you change your oil , do your engine a favor and go to a FULL SYNTHETIC. "Blend" may contain an insignificant amount of synthetic. The BEST Synthetic on the market today for your car is Amsoil Z-Rod. Look it up. In 10W/30 and 20/W50 (mix 50/50 and get 15/W40). It is also specifically formulated for corrosion protection during lay up periods. There is an alternate school of thought on oil for old cars. Goes something like this : "The WORST oil today is better than the BEST oil way back THEN". This is used to justify using less , or FAR less than the BEST oil available NOW. I LOVE my old cars. No ! Really ! I seriously DO love my old cars. LOVE , man. TRUE LOVE. I do not change my oil twice a week , so feeding them the very BEST oil I can possibly find is a negligible expense figured against the total cost of owning these beloved toys. Not that I am looking to cut corners on anything , I would use the best oil even if I DID change it twice a week. But I don't , you don't , and niether do the alternate school boys and girls change oil much more than two or three times a year , if that. I figure the best lubrication possible might just prove to be the cheapest option , considering the cost of repairs to machinery. Use synthetic grease also. 

 

Time me for me to sign off here with the necessary disclaimer : I have absolutely no affiliation whatsoever with Amsoil. I just use their products. If anyone can show me better , I will drop Amsoil "Before you can count , one , two , three. Yes I will. Yes I WEEEE - il !". As the song goes. 

 

I hope the the above logic makes some sense to you , 1Aries.                             ,  ain't "Snake oil".    - Carl 

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Not all SAE -30 oils have the same viscosity (there is a range they must be in to be called SAE -30) so the oil pressure will vary. Have a look at Widman's paper on it and see how they vary.

http://www.widman.biz/Corvair/English/Links/Oil.html. You can see how the viscosity ranges and SAE grades compare with an oil chart like this from https://bobistheoilguy.com/viscosity-charts/:

Viscosity Chart

 

Keep out of SAE anyW-50 oil unless your engine is pretty worn, or to be blunt, stuffed. Your engine was probably designed for SAE 30 oil, maybe SAE 40 in the high summer when your temps are really high (90s).

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20W/50 is too heavy re : temp/viscosity operating envelope as per "Widman". Furthermore , if you are using Castrol dinosaur lard , you know what you are getting. However , if you are using "synthetic" Castrol , please understand that there are degrees of syntheticity. Castrol is right about at the bottom , Amsoil right up at the top , with others in between. Yes , modern high quality multi grade oil , frequently changed does a pretty good job most days. However : all  engines have hotspots , and all engines if they accidentally overheat , need the maximum protection possible to give them the greatest chance of survival. It is a film strength and flashpoint thing.  I am currently using Amsoil Z-Rod 20W/50 in the desert Southwest in my 1927 Cadillac , and have encountered temps of 100+ during midday. Maximum Summer sun angle has cooked the pavement , and the re-radiation into the undercarriage and engine compartment is a significant factor. When I finally do get the old thing back to the cool cloudy Northwest , I think I will go to the 50/50 mix I mentioned above. Amsoil does have a unique characteristic , in that their synthetic oils  behave like a lower viscosity when cold than their nominal spec. This allows faster pumping on startup. Please re-read my disclaimer above , and please read "Widman". Richard Widman professes the same disclaimer as I do. Many of us feel fully justified in believing he simply "tells it like it is". Reading his 33 pages at least once or twice is time well spent.     - Carl 

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I agree Carl.  The synthetic gives you extra margin in oxidation resistance, flash point, etc.  so if something unexpected happens you are less likely to seriously damage expensive engine parts.  

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There are so many articles and points of view written about use of oils in older engines one could write a long book. Much of the discussion deals with use of modern oils with declining levels of zinc, which was a valuable additive relating to V8's of the 60's and 70's, when it acted to keep wear surfaces "repaired". Close tolerance modern engines benefit from synthetics, whose slickness helps keep parts lubricated at high RPM's and minimizes wear or overheating. My understanding was that for older engines (pre-war), where close tolerances is not the issue, and where there is a need for "stickiness" to keep parts lubricated especially when the are left to sit for extended periods, that regular weight "non-synthetic" engine oils are best, they have the right combination of being sticky, and viscous enough to meet the designed engineering needs of such engines. As someone suggests, the worst of these is likely as good as the best available in the 30's. A decent 10/30 oil kept filled and changed annually will do, and if there is no filter, common for old engines, check regularly for signs of dirt in oil. Just my $2C worth.

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