What weight oil?
 

OK, here's an easy one (I think): what weight motor oil is best in the warmer months? 10-40, 20-40, 30?

It gets pretty warm here in the Washington, DC area. I run a 351W (AFR heads, Speed Demon, MSD, mild cam).

Thanks much.

The guy who built my motor recommended Mobile 1 15-30. It is a stroked 351W that is pretty stout.

20/50 unless advised otherwise by your engine builder. or call svo techline but suspect they will also say 20/50 . bill

Ed,
There are many factors to consider on this subject. Engine clearances, compression ratio, operational range(rpm), etc... You should consult your engine builder to make sure you have all the data. A couple GENERAL rules: You should avoid synthetic oil during break-in time, usually at least 5000 miles. Multi-weight oils assume their range by season, meaning 10w-40 or 20w-40 will behave the same in the summer, as they are both 40w at warmer temps. There is lots of detailed information on many company websites, such as RedLine, where you can pick up lots of good information. But, the first step is to understand your engine.
Hope this helps!
~Dave

Dalola is correct, engine design parameters are the determining factor. That being said, many "experts" are saying that the old tried-and-true 20W-50 is old technology, that there are now better choices. General Motors Performance (yeah, it's not Ford!!) even reccommends using synthetic 0W-10 for certain racing venues.
auto10x
Bill

Ed,

After break-in, use the lightest weight that gives good oil pressure. Lighter weight oil is easier for the engine to pump around and if your clearances are tight enough will give you the most power and the best efficiency.

My engine was built pretty loose. After break-in, I tried 10-30 synthetic and the oil pressure at idle, hot, dropped under 20 psi. I switched up to 20-50 and the pressure is fine. Now, I'm trying Castrol Synthetic 10-50. It is OK most of the time, but when I'm idling a long time (in traffic), the pressure gets a little low. I'll go back to 20-50 Mobil One next time.

Paul

Just for the record, Mobil1 comes in 0W-40, 0W-30, 5W-30, 10W-30 and 15W-50. Ford Motorsports told me to use 5W-30 in my crate 351, which I use year-round. My pressure is never below 55PSI on the road.

Paul is right on the money when he says use the lightest weight oil which will give you good oil pressure. Viscosity which causes the relief valve to open will reduce flow to the places it need to go. Keep in mind that most of our cars have an oil cooler which reduces the need for heavier weight oils.

Bob

OIL VISCOSITY.
 

20-50 CASTROL GTX FOR ME IN THE SOUTH. PRESSURE IS KING WHERE HEAT AND A SUPERCHARGER IS INVOLVED.

IT SEEMS THAT THE SYNTHETIC RECOMMENDATIONS ARE BEING CROSSED WITH THOSE APPLYING TO THE NEW-TECH ENGINES LIKE GM'S LS-1 AND FORD'S OVERHEAD CAM APPLICATIONS.
THESE ENGINES HAVE FAR DIFFERENT SPECS THAN MOST FOUND IN OUR COBRAS.

AFTER ALL, IT IS AGAINST FEDERAL REGS TO USE SYNTHETICS IN A PISTON AIRCRAFT MOTOR DUE TO HUNDREDS OF ENGINE FAILURES USING SYNTHETICS.
(THIS IS COVERED ON ANOTHER THREAD)

JUST BE CAUTIOUS. "SOMETIMES", NEW-TECH DOESN'T MIX WELL WITH OLD-TECH.....
OR OLDER MAY BE BETTER....WHO KNOWS ?? LOL...

B. SMITH

Bob,

That's the second time this has come up. I have a case of Mobil One Synthetic oil in my garage clearly marked 20-50. I can post a picture if you don't believe me. Maybe oil companies distribute different products in different parts of the country?

I will do a search for the aircraft engines failing. Is there any explaination?

Paul

Ah, but in an experimental aircraft running an experimental engine you can run any oil you wish. If you are running a "certified" engine you must comply with the manufacturers recommendations or the FAA will spank you. Most if not all US certified, piston aircraft engines are of 1930s design although they have had many evolutionary changes along the way. It's just too expensive to certify a new or "revolutionary" aircraft engine given the volume of powerplants sold. When was the last time you saw a car running a magneto (other than at an antique car show)? Check your local airport and many of the bug smashers there use them.

So, in my experiemntal cobra with my experimental power plant synthetic oil is A-OK. :D

Paul:
According to their web site I have the viscosities correct, take a look - www.mobil1.com .

Bob

Thanks for all the useful information. My engine builder (Performance Engineering) says 20-50. "As for synthetics...well..." His voice kind of trailed off.
Ed

I have a case of 20w50 Mobil1 in my garage. Picked it up at K-Mart of all places. I'm in GA.

My two cents worth.

Heavier weight oils are fine for engines with increased clearances, but for stock clearances a reduced viscosity oil is required to insure oil flow. Oil flow is what ultimately keeps the bearings cool and if the oil flow is inhibited by a higher viscosity, then the bearing gets hot and ultimately fails.

Overhead cam engines require very low viscosity oil mostly due to the extreme lengths the oil must travel to get to the heads and supply an adequate flow of oil, especially when the oil is cold.

:confused: "AFTER ALL, IT IS AGAINST FEDERAL REGS TO USE SYNTHETICS IN A PISTON AIRCRAFT MOTOR DUE TO HUNDREDS OF ENGINE FAILURES USING SYNTHETICS."

This is a new one on me. Recip. aircraft engines did have problems with Mobil synthetics and the resulting engine failures and law suites when it was first introduced for aircraft use, but there's no blanket restriction by the FAA on synthetics. I've been using AeroShell 15W50 with AvBlend legally for several years without a problem. The 15 viscosity is great for lubricating on cold startup, but would be too thin at operating temps, so the 50 viscosity kicks in for maintaining pressure with the wide clearances required in an air-cooled aircraft engine.

I've been using Mobil 1 20W50 in my 427 so with good results. Such a thick oil should only be used if oil clearances are wide, otherwise I'd go with a 10W30 or whatever the engine builder recommends. But the 20 psi at 3,000 to 5,500 rpm at 90 to 100C was too low with 10W30, thus the move to 20W50.

Note that new production engines are tightening up clearances, which require a much "lighter" oil, such as 0W30 or 5W30 so they will be lubricated on cold startup. Why the tight oil clearances? . . . so oil pumping loss will be lower, thus more power at the crank and less fuel out of the tank. Why loose clearances? . . . for engine cooling. More oil flowing carries more heat, which is not necessary for most street engines or many race engines with oil coolers.:)