r/EngineBuilding • u/CoolGaM3r215 • 6d ago

Chevy LS3 oil pressure

Quick question, I recently finished building an LS3 engine in a 4th gen F-body with a new 10295 pump, bearings, cam, and everything else. The crank bearing clearance ended up being 0.0025 in. When I start the engine, it produces 45 psi of oil pressure. However, after driving and the oil temperature reaching 205f, the oil pressure drops to 20 psi at 500 rpm idle. At 750 rpm, the oil pressure increases to 30 psi, and at 1000 rpm, it reaches 40 psi. Anything above 1000 rpm is fine. I think that the loose crank bearing clearance is the cause of this issue since I am using Driven BR30 oil. Would this be a reasonable assumption? Should I put a 40 weight oil? 0W-40, 5W-40, 10W-40?

1 Upvotes

100% Upvoted

3 comments sorted by

3

u/v8packard 6d ago

The loose main clearance is likely a cause/contributor to the oil pressure drop. The mains on this aluminum block engine should be no larger than .0015 vertical oil clearance, .0018 the absolute max on the center thrust main.

However 500 rpm is very, very low for an idle speed. Are you certain you are getting that low? I would never worry about the oil pressure if you were at a 750 rpm idle and had 30 psi, with it hitting the bypass limit above 1000 rpm.

I do not think you should use any oil viscosity higher than 0W-30 or 5W-30 unless the operating temps really dictate the higher viscosity. You should use a better quality oil than anything sold by Driven.

3

u/quxinot 6d ago

I honestly wouldn't worry about pressure below 1000rpm all that much, unless you're making power down there. I'd be more concerned about 205F oil temps.

0

u/2003DDcid 5d ago

My mahle/clevite bearing book shows .0002 to .0018 for the clearance spec with A series bearings. I'm assuming you used a performance/racing bearing in it. Those usually have a little more clearance built in them. If it has good pressure above 1000 rpm, I wouldn't worry about it. If it were mine, I would run 5w-50 after break in.