Synthetic oil equivalent of 15W40?
 

My engine builder recommended I run 10W40 or 15W40 dino oil in my car.

I wanted to run synthetic.

What would be the synthetic equivalent of Quaker State 10W40 dino oil? 15W50 Mobil 1 Synthetic?

From what I've seen, the next thinner grade synthetic will provide oil film strengths that are greater than the dino oil being replaced. Meaning, a 5W30 synthetic is preferable to a 10w40 dino. Plus you'll gain a tiny amount of power due to less friction with the lighter synthetic.

i just started running 15W/40 Royal Purple. So far so good! Id recommend it.

I'm not sure if I would go thinner.

I was wondering if 15W50 was too thick.

Mobil1 claims its for high performance motors.

10w40 = 10w40
dino=synthetic

The oils meet the same viscosity standards to get their respective ratings. Synthetics may provide slightly better lubrication and resistance to breakdown, but their viscosity must be in the same standard ranges as conventional oil to receive the same cold and warm viscosity ratings.

Ask your builder if he was recommending a dino oil for break in. That is a controversial topic though.

-brent

Your missing the point. The viscosity may be identical, but the oil film strength on the bearings will be stronger with the synthetic, which is why you can run the next viscosity grade down.

You *could* run a lighter synthetic if you were made of money and looking for a couple HP on a race motor. I'm not sure that is what Bottlefed is looking for though. For longevity i'd still recommend sticking with the builders recommended viscousity.

Viscosity is a physical property that relates to the oils abillity to hydrodynamically lubricate the bearings given the oil pressure, pump capacity, and tolerances. Hydrodynamic lubrication is what we want for minimizing wear.

I'm not aware of any direct measures of film strength other than measures of wear which imply better film strength. I could be wrong and there is some way to directly measure film strength. I said that synthetic provides "slightly better lubrication". What I meant by that is that the superior chemical composition has better film strength and lubrication.

This only comes into play when the lubricant is acting like a boundry lubricant. Both the base oil (synthetic vs dino) and the antiwear addatives which could be added to each base stock come into play here.

If you choose to run a lighter weight synthetic you are sacrificeing some of the oil's ability to hydrodynamically lubricate and relying on boundry lubrication. Why not have the best of both worlds and run a synthetic of a viscosity matched to the bearing tolerances and pump capacity/pressure?

I'm not an oil Phd though so i'm open to discussion/response :)

-brent

I like Mobil 1 0W-40, but it's COLD here in Chicago.

So the question is, do you run the same weight as dino oil or do you run a higher one?

Well, I'll leave it at this. My motor makes over 650 fwhp and has done it for two years of street/track use with Mobil 1 5W30. Prior to that, the stock short block belted out 500 fwhp, and at 70,000 miles, the cylinder cross hatching was still mint, and the bearings looked awesome. That was also with Mobil 1 5W30. So I'm gonna stick with the hot hand! :)

Ok but what about for guys that have more clearance and need to run a thicker oil?

I've always been told that synthetic was thinner so I should go a little thicker than my reg oil?

you said your engine builder recomended this oil......do you think its possible that he recomended this oil for the engine break in and may not have been totaly clear about its future use?

Pretty sure.

he said the bearing clearances were greater.