What oil should I use?

[Lou C]

I have used both the Merc/Quicksilver conventional 25/40 and the syn blend 25/50. Did oil analyses on both and found they both hold their viscosity well. The syn blend 25/50 has more zinc (1240 or so) than the conventional (940 or so). However, keep in mind that if your engine has a roller lifter cam, you don't need the higher levels of zinc that benefit flat tappet cam engines. The 4.3 got the roller cam as far back as '87/88, my '88 definitely has a roller cam.

 

[Scott06]

I was considering only Vr1 oil 20w50 because it has more ZDDP in its blend than 25w40, I’m changing oil annually and don’t run my V6 hard barely above 3000rpms usually 2500/2700. Thanks and I’ve got around 15-18psi @ idle

As Lou said you don’t need so much zddp with a roller cam. Flat tapped different story. What you describe the 25-40 is fine. I found on long high rpm runs the oil pressure would get lower some times down to 40-45 psi at 4500 or more rpm. Was thinking maybe oil is foaming or getting more oil up in cylinder head not draining back…. Tried adding half a qt then lowering half a qt … 50 wt seemed to cure it.


the 50 wt holds oil pressure after long runs.


really you are not driving it hard enough you are not using 40 % of the available rpms….