What do you other Vette owners think of using 15-50 full synthetic (Mobil One) in a '98 C5's LS1?

What about in a '67 Coupe's 327/300?

A S.Calif. friend says he runs that weight in all half-dozen of his vehicles (racers thru trucks)... and says as long as I have a heated garage where the cars never get below 50º all winter they should run fine --and cooler-- all summer on the thicker oil.

So what's the opinion out there?

 

I think that's a very bad idea. Mobil technical assistance reps have told me more than once that even at 70 degree F startup temps, oil needs to be thin enough to be pumped up to pressure quickly and easily, since most engine wear occures at startup, even during mild temps. In fact, the Mobil reps have stated that there is really no valid reason for most Corvette owners to use anything thicker than a 5W (on the low side of the viscosity rating) oil. Some 0W-30 and 0W-40 synthetic oils are also good choices, but the only time I would use 10W-30 oil would be if it were recommended by the factory, as was the case with my crate ZZ3 engine that was installed in my 68. This would (more than likely) be a good choice for a 327 if factory tolerances were upheld during rebuild and ambient temps never dropped too low.

 

The thinner oils are also much cheaper to produce than the thicker ones. You young guys weren't even born when sports cars and race engines ran on 30 or 20-50. The thinner multiweight oils are a by product of a marketing department gone wild with the desire to get rid of the thin oils that were being produced as a by product of making 'normal' weight oils. Back in the early 80s my Dad sat next to an oil exec on a flight and he volunteered the taudry deal about the then 'new' 5 and 10 weight compinent oils. They had been just blending the 0, 5 and 10 wt. oils into heating and 'bunker' oils, and there was a desire to sell at higher prices] Today these thin oils, which consume a bit less energy to pump up to pressure, are part of the 'low friction' [ in NEW engines ] plan to help manufacturers like GM improve their CAFE ratings. [Corporate Average Fuel Economy] One tenth of an MPG over a hundred thousand cars makes a big difference to the CAFE! There is no proof ever been offered that thin oils improve engine longevity, in fact quite the opposite seems to be what the race engine builders I know are saying. Once you have an older engine and clearences are larger due to wear, thicker oils will help take up the slop. I have a 98 LS1 with 71K miles. I use the thicker 15-50 Mobil one you are mentioning because a VERY SUCCESSFUL race engine bulder I know tells me that I'm stupid to use thin oil in my older engine. So does the mechanic and shop owner at my 'regular' service shop...[The shop owner there has owned 3 C5s!] This agrees with everything that I have learned over 35 plus years of my own experience of being around the sports car scene, and engine builders serving both the street and race markets.

So what did I find after switching from water weight Mobil 1?......

1.Quiter start up....common among LS motors, piston slap until pistons warm up is much quieter,

2.Quicker pressure build-up when starting engine, hot or cold,

3. More oil pressure at idle when the engine is fully warmed,

4. Engine reaches full oil pressure at slightly lower RPM

REMEMBER THIS, ..contratry to what Dave68 says he was told by Mobil 1 reps, the protection film left by a thicker oil when the engine if shut off will be thicker and harder to scrape off than thin-runny oil, and when starting up, the ONLY protection your engine receives is from the film left behind, ....until the oil pump starts pumping up pressure. Thicker protects better!!!..... and comes up to pressure quicker. By the way, I grew up in Minnesota...REALLY COLD WINTERS, and 10 or 15 weight oils were commonly used there in the winter. The 0 and 5 weight oils are 'newer', contrived to sell by-products of making thicker oils. Remember, prior to the 80s, these oils were blended with heating oil just to get rid of it! O and 5 wt. oils are runnier at VERY cold temps, but as the engine wams up and the oil temp rises, it gets too thin to really protect as well as thicker oils. Choosing a balance in character and performance is important, as really thin oil cranks easy at super cold temps, but gets too thin at operating temps, so you have to compromise somewhere. I now live in NW Oregon where it rarely drops into the +20s, let alone colder, and we use 20-50 in all our cars, except the Vette, where we now use 15-50....and in every way it seems much better than 0-30 that was in it when I bought it. You will find that most of the owners on the furum will follow the advice of GM, who has a CAFE rating to maintain, and who MUST hold to the story of 'thin is better', even if untrue, and the oil makers have their own axe to grind too....thin oils are cheaper to make, MORE PROFIT.....So its not so easy to get to the bottom of the story. So far, the experts I listen to are independant engine builders who have nothing to gain one way or another, other than to report what they see in engines they build or maintain. Knowing some of the 'secret' history of how and why thin oils were brought to the marketplace also helps you understand why they are here, and why they are so strongly promoted. Its YOUR choice, and you will find all positions about thin VS thick well defended by their supporters. Good luck figuring it out for yourself