Oil Pressure
 

Will be changing to a new grade of oil this week because 15w50 FS is a little thick. On 10w50 FS what pressure readings should i expect?

4 year old EJ20 cdb engine

Cheers. Andy

Im 99.9% sure that 15w50 and 10w50 are the same thickness as it is the second number that determines how thick the oil is and the first number is something to do with protection of the engine when cold, i.e a 5w will give better cold protection than a 10w.

If you want to try a thinner oil than a 15w50 then i would say a 10w40 is appropriate.

I think the 2 numbers represent the "weight" from cold and hot. 15w50 is too thick from cold

Your right they are the same when "hot"

if 15w50 is to thick from cold, then yeah a 10w50 would be better for cold start etc.

I did this on my 03 WRX and have not noticed a difference on my Defi's. The 10w will be better cold than the 15w. There are figures I have looked at but it got too heavy and complicated for me. If you require more info then contact one of the Opie oil guys.
I made the swap for the better cold start properties. There is a difference in properties and that is fact, but I will paste some figures here from Opie website.

Fuchs info for 10w50, http://www.opieoils.co.uk/pdfs/New-F...RO-S-RANGE.pdf
Info for 15w50, http://www.opieoils.co.uk/pdfs/New-F...O-R-15W-50.pdf
If you look around the Opie Oils website, you will find more comparative data.