Nascar oil pressure

[GRTfast]

I have been running 20w50 VR1 in my big block sinciie day one. It idles hot at 35-40 psi, cruises at 60-65 psi and peaks at 80 psi. After reading a bunch of stuff including this thread, I have switched to 10w40 Mobil 1. All the above numbers are reduced by 5-10 psi. I'm wondering if I should go even lighter. The old school thinking is so ingrained in me that it's hard to think I could use 10w30 or something comparable in my motor.

I have an honest and probably silly question; did the reduction in pressure come from the 20w to 10w drop or the 50 to 40 drop? Some of both?

The way I understand it, multi viscosity oils are a base oil of the lower number, with certain polymers that expand with heat and make it behave like a higher weIght oil at elevated temps. Because of that, I’d say both.

[MadBill]

The 'W' rating is assessed at various* low temperatures (*depending on the grade), representing a winter cold start. The second number is at 100° C. or 212° F. and so is indicative of a warmed-up engine.

[RDY4WAR]

I have been running 20w50 VR1 in my big block sinciie day one. It idles hot at 35-40 psi, cruises at 60-65 psi and peaks at 80 psi. After reading a bunch of stuff including this thread, I have switched to 10w40 Mobil 1. All the above numbers are reduced by 5-10 psi. I'm wondering if I should go even lighter. The old school thinking is so ingrained in me that it's hard to think I could use 10w30 or something comparable in my motor.

I have an honest and probably silly question; did the reduction in pressure come from the 20w to 10w drop or the 50 to 40 drop? Some of both?

The way I understand it, multi viscosity oils are a base oil of the lower number, with certain polymers that expand with heat and make it behave like a higher weIght oil at elevated temps. Because of that, I’d say both.

That is correct for conventional oils at least and some synthetics. (group III synthetics or what I like to call "fake synthetics") PAO synthetic oils (group IV and V) have a much wider natural temperature range without requiring viscosity index improver additives. They don't fluctuate in viscosity as much in extreme cold or heat.

With a conventional oil, they have to add VI improvers to the oil in order to get a multi-viscosity rating. For a 10w-30 for example, they take a 10 grade oil and add VI improvers that expand with heat and resists thinning out. So when it's cold, it's a 10 grade but warmed up, "acts" like a 30 grade. The problem with VI improvers is they are consumable additives. With heat and shear, they wear out. As a result, over time that 10w-30 becomes a 10w-25, then a 10w-20, and eventually just a 10 grade when all of the additive is worn out. PAO synthetics don't require VI improvers so they can use a straight 30 grade base oil with no VI improver and it have the same cold and warm viscosity as a 5w-30 or 10w-30 conventional with the additives and will get labeled as a multi-viscosity based on those ranges.

I know this thread is about NASCAR but on the street, the oil temperature and coolant temperature can vary wildly with each other. On my car, the oil takes much longer to warm up than the coolant. After driving 5 minutes down the road, the coolant temp will be 190-195*F and the oil temps still around 130*F. It can take 10-15 minutes cruising down the highway before the oil gets up to 200-210*F.

[RevTheory]

Thanks for the info, fellas, and I apologize for the threadjack.

[GRTfast]

The 'W' rating is assessed at various* low temperatures (*depending on the grade), representing a winter cold start. The second number is at 100° C. or 212° F. and so is indicative of a warmed-up engine.

That’s correct. The way they achieve an oil that behaves like a 10 at cold startup and a 40 at running temp is by using special polymers that expand (and increase viscosity) when they heat up. At least that’s what I read the other day. I’m a mechanical engineer though, not a chemical engineer. That stuff is black magic.