hi lads wots the best cheap oil to use to flush a cosworth motor out with befor putting it nice new oil in .

Becuse as of late my oil pressher has dropped from 40psi hot to 34psi and at about 2,500rpm its at 50psi and was at about 58psi befor . and i think i have a very small nock But its not all the time we tuck it for a drive last night pulled up and i think i herd some thing but as qwick as it was there it was gone im hopping its just the oil has gone off as it all sounds good when when cold . This motor has only done 3,000 miles sins it was built

WOT DO YOU THINK