Oil is a tough subject. Partly because the oil makers keep the info close to the vest, and partly because there's a lot of mis-information on the web. Here's some basic facts about engine oil:
1. Viscosity:
You need a "heavy" enough oil to maintain proper pressure in all situations. What that is, exactly, varies from engine to engine. Anything mor than about 50psi is more than necessary, and wastes energy producing the pressure.
Too thick can wear on the drive mechanism, and shear gear pins. It will not produce appreciably higher pressures, because the pump has an integral pressure release valve.
Oil "thickness", "weight", and viscosity are usually displayed as two numbers; as in 10W-40.
The 10W means the oil will have the viscosity of a 10 weight oil when it's cold. The W stands for Winter.
The 40 means it will have the viscosity of 40 when a 40 oil is up to operating temp. That does not mean it will have a viscosity of 40 when hot.
I use a 10W-40 oil and never have trouble maintaining 45-50PSI in all situations, even when the oil temp rises to 240*.
2. Synthetic Oils
A true synthetic starts with a PAO base stock. There are no dino oils in it.
AFAIK, there are only 4 on the market: Red Line, Royal Purple, Amsoil, and a nother one I can never remember.
Other so called synthetic oils start with dino oil, and is then refined enough to meet the specified performance standards of a synthetic oil. It's a trick of lawyers and marketing. Most people don't know the differance.
Mobile 1 is NOT a true synthetic. It's a fine oil, and will work just fine in most situations. But it's not a true synthetic, and probably not any better than QUaker State, Penzoil, Castrol, etc. If the price is comperable, don't be afraid to use it.
True synthetics have two big advantages. They are more heat resistant. They withstand higher temps for longer durations without breaking down. 240*for 30 minutes for a true synthetic is not a big deal. They also last a lot longer than dino based oils. A 10K mile drain interval for a DD is pretty reasonable.
3. Change intervals.
3000 miles is OK if you have an old dirty engine, or use leaded fuel. The only people who routinly still recommend changes that often either sell oil or oil changes. Many people change it that often because that's what grandpa did, and he was a mechanic for 30 years. Those people have not kept up with modern technology. And some people use cheap wally world oil and change every 3K miles because it helps them sleep at night; and that's OK, to.
I use Royal Purple, and change it about twice a year. I race with leaded fuel and beat on it pretty hard. I also use RP in my DD, and change it every 10K miles.
4. Flat tappet cams
In the past, oil had plenty of ZDDP as an anti-wear additive. Because of emissions reg, most of it was pretty much eliminated. Even diesel oils have decrease the ZDDP by about 25%. This is one of the facters that contributes to increased lifter and lobe wear. Comp Cams has an excellent white paper on this subject. If you're interested, be sure and read that.
There are a couple of additives on the market that will increase ZDDP to previous levels. Some racing oils also have higher levels. But you can't use them on any vehicle that has a cat.
After reading the white paper from comp cams, I wouldn't build an engine with flat tappets.
So, here's my general recommendation for most Cobra owners.
1. Use a decent Dino oil for street use, and a true synthetic for racing.
2. If you have a flat tappet cam, add some extra ZDDP
3. Change it once a year for steet use, and 2-3 times a year for occasional track use.
4. Use the lowest viscosity that will produce the proper oil pressure in all situations. a 5W-30 is probably right for most people.
But, that's just my opinion. I could be wrong.
Oil change
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