My 74 manual says to use 30wt oil with temps above 40* F and 5W-30 in Canada. :laughing:
It does show multivis oil as being usable using 10W and 20W with multiple grades.
My 77 F100 manual shows straight vis as well.
Dep, the engine design is still the same. The bearing clearances are the same as the original and on and on.
Every time I put multivis oil in a '60's and 70's engine, rebuilt or not, my oil pressure (on the gauge) drops from 5 to 10 PSI.
Multivis oil is made with polyimers which control the viscosity. The polyimers make up a relativly large amount of the "oil". Polyimers add no lubrication properties what so ever.
Well I sure don't understand it. My Dad was a BIG user of 10W30 oil most of his life and NEVER had a problem with leakage or anything else. And that was with cars from the late 60s right up into the 90s from Ford, GM, and Mopar. Ford recommended 10W30 for MANY years. Last time I used straight weight oil in anything was a lawnmower back in the 60s. Even my new Sears lawnmower uses multigrade oil. NASCAR and NHRA are all using multi-grade oil in their race engines (with the exception of the blown nitro engines).
About oil pressure gauge readings:
"The key words in the previous post of mine which you described were "...ACTUALLY NEEDS...". In other words, if an engine is set up so loose that it "ACTUALLY NEEDS" 15W-40 oil to maintain proper oil pressure, that could mean that it's set up too loose for dependable, long-term street service.
All 1969 Corvettes, including L-88s, should operate with normal oil pressure using 10W-30 weight oil. However, for ambient temps above 20 degrees F, 10W-40 or 20W-40 were approved engine oil viscosities. In my opinion, the latter 2 viscosities would be the preferable ones for use in an L-88. But, the L-88 engine should maintain normal oil pressure with 10W-30.
L-88s used a standard volume, high pressure oil pump. The high pressure pump was designed to "overcome" or compensate for some of the "looseness" in the engine set-up. Idle oil pressure shoud be about 20-25 psi. Keep in mind, however, that the original in-car oil pressure gauges are rather notoriously inaccurate. Usually, they read 5 to 10 psi LOW. To determine what actual oil pressure that your engine is running at, you need to temporarily install an accurate, high quality test gauge."
This from the Mobil 1 website:
Myth: Mobil 1 will leak out of the seals of older cars.
Mobil 1 does not cause leaks. In fact, new Mobil 1 was tested in dozens of industry standard and original equipment manufacturers (OEMs) tests to prove its seal performance. It is fully compatible with the elastomeric materials from which all automotive seals and gaskets are made. If an older engine is in good condition and does not have oil leaks, Mobil 1 provides the same advantages as when used in a new engine. ExxonMobil recommends taking measures to repair the leaks, then using Mobil 1. ExxonMobil also recommends following the automobile manufacturer's manual for the proper oil to use.
From the NASCAR website:
Ever wonder about synthetic oil and how it compares to petroleum based oil? Well, the word "synthetic" means it's made with a combination of chemicals, so synthetic oil is "designed" while crude oil is "refined."
Synthetic oil contains a uniform molecular construction that's created to perform consistently under the harshest circumstances. It also starts out contaminant free, which is impossible for traditional petroleum based oils.
Starting the engine is tough on all of the internal parts, which is why many people appreciate synthetic oil's adhering quality. Even after the car stops, there is a film left to coat the engine parts, protecting them during the next start up.
Finally, because synthetic oil doesn't break down, it doesn't have to be changed as often. Certain manufacturers claim oil change intervals as high as 25,000 miles, justifying synthetic oil's high price for some motorists.