JohnJan

I wonder if Merc recommends against synthetics because of the contradiction in claims of extended change intervals. Merc says change every x hours and the synthetic manufacturers say you can change every y hours (or miles).

We all know the change interval on marine engines needs to be relatively often. Changes occur long before the lubricating properties of a petroleum based oil breaks down. Sterling, and other racing engine mfgrs can be pretty sure that their engines are getting the oil changed regulary, but what about the typical boater with a Sea Ray? Sterling and those guys are selling engines to be used under extreme conditions, well beyond those of the average performance boater and they're claiming hp #s that may rely on the extra itty bitty teeny weeny bit that can be measured with synth oil.

I run my 509 with straight 40w petro and change the oil every 20 hrs or so. Any teardowns over the years have shown very little wear on bearing or cam surfaces. If I were to run synth oil I'm pretty sure I'd be wasting my money.

Also, I run my truck on petro based, GM recommended 5w-30 or whatever it is. Change oil every 5000 miles. 140,000 miles later, 60,000 of which has been with a Whipple running up to 6 psi boost I did a leakdown which was less than 5% on all 8 holes. If I were running Mobil 1 in the truck I think that'd be a waste of money as well.

mcollinstn

There is no doubt that modern conventional motor oils are very very good. Motor oils have come a LONG way in 20 years.

The fact remains that a synthetic will give far superior low temp performance and will flow well at low temps. Synthetics will give superior HIGH temp performance and will not thin so dramatically at high temps. Synthetics have higher lube film shear strengths which offer better results on flat tappet cam lifters, stamped rocker arms, distributor gear and oil pump components.

Motors using the correct size crank and rod bearings for their horsepower output will support their rotating components just fine with conventional lube stocks (as long as oil pressure remains within spec). Supercharged smallblocks with "smaller than optimal" rod and crank bearing surfaces for their output will see a significantly enhanced measure of safety by using synthetics.

I agree that 100% premium synthetic motor oils are certainly overkill for any Big Block under 500 horsepower.

But at a cost of an additional $20 per oilchange, it just doesn't enter into my "wasteful spending" category.

People certainly have different preferences on their motor oils. That's why there are som many to chose from.

(I also have a buddy that takes my "used" Mobil1 and runs it in his trucks and lawnmowers.)

Scott

Quote from mcollinstn

"Synthetics will give superior HIGH temp performance and will not thin so dramatically at high temps"


This is the #1 reason to me why it is worth the extra $$ at each oil change. The one time you over heat because of something stupid it may just save the engine.

Cheap Insurance