How to Determine the Correct Oil Grade for your Car

[madeej11]

I have been away from the site for years. It seems now I have some time on my hands as I am close to retirement.

Anyway, it is simple: The rule is that you need 10 PSI for every 1,000 RPM of engine speed. I generally like to keep it as 8 - 12 PSI.

In a thread somebody was asking what grade to use. He stated that he mostly drove “normally” but on occasion was on the track. He got all sorts of advise but the correct response. He needs two oils, one for each application. He needs to use whatever oil gives him the appropriate PSI for his different applications. It’s that simple.

FYI, my Ferrari 812 Superfast normally runs at 35-45 PSI at idle (650 RPM) at normal operating temperature while driving around town, my only application. The oil temp has never been above 170F so far. The oil is a 40 grade but surely I can use a 20 grade safely. The maximum oil pressure is limited to 80 PSI at 9,500 RPM because of the pop off pressure valve. So Ferrari thinks that 80 PSI is enough for 9,500 RPM. They do caution that the engine must be fully warmed up before running up the RPM - Why? They do not want the oil to be too thick with higher RPM.

AEHaas

35-45 psi at idle seems quite excessive unless I'm clueless. Am I?

 

[Bill_W]

Along with the help of CAFE.

My understanding CAFE was adjusted to SAFE…

 

[ZeeOSix]

35-45 psi at idle seems quite excessive unless I'm clueless. Am I?

My Z06 was 32 PSI at idle with 5W-30 at 200 F.

 

[madeej11]

My Z06 was 32 PSI at idle with 5W-30 at 200 F.

Thanks Zee, your word always seems to be dependable. Guess I am clueless.

 

[AEHaas]

My Z06 was 32 PSI at idle with 5W-30 at 200 F.

How about 3,000 RPM at 200 F?
Ali

 

[ZeeOSix]

How about 3,000 RPM at 200 F?
Ali

Here's a plot of the data I took. At 3000 RPM the oil pressure was 56-57 PSI. All data in the plot below was with oil at 200 F.

 

[Bill_W]

Here's a plot of the data I took. At 3000 RPM the oil pressure was 56-57 PSI. All data in the plot below was with oil at 200 F.

View attachment 84673

What does your OM say for viscosity?

 

[ZeeOSix]

What does your OM say for viscosity?

5W-30, which is what the plot above is with. I always used Mobil 1 full synthetic.