390 using a quart in 600 miles

[390owner]

My rebuilt 390 is using about one quart of oil in 600 miles. It is not smoking. It runs like a champ. I have put about 3000 miles on it since the machine shop did a complete rebuild. I have changed the pvc valve. The machine shop said just drive it and keep him posted. Where is the oil going? I do not want to pull this engine again and take it back to him Any ideas??

[GerryP]

If you don't have any puddles in your driveway, the oil is being burned.  A quart every 600 miles isn't enough to create a mosquito fogger.  You should see the evidence on the spark plugs, though.  There will be ash deposits.

Your machine shop screwed the engine together and they have an obligation to diagnose the issue.  You should drive the car to them and have them look it over.  It could be going past the rings, past the valve guides, or past the intake manifold gaskets.  It could be sucked up by the PCV if you don't have a baffle in the valve cover.  A new PCV won't fix that.  Regardless, your machine shop has an obligation to get to the bottom of it.

Your machine shop's advice to keep driving it and keep him posted just means he can't look at it right now.  It will not get better with time so don't expect the problem to heal itself.  It won't.

[KMcCullah]

Bummer about your new engine. I'd follow the shops directions and drive it. Drive it like it's rented in fact. The rings might be slow to seat if the hone was rough. Hit a few mountain passes. Or latch on to a chunky camper. Work that FE.

Take a look down the intake runners with borescope, might show a leaking intake gasket.

[TJ]

Could look down the carb and see if you have oil puddles in the intake. If you do, try disconnecting the PVC and replacing it with a breather.   If that doesn't stop it, might be an intake leak.  It's harder to prevent oil leaks on these intakes than it should be.

[390owner]

I did have a pvc problem a month or so ago. I thought it was my chrome valve covers so I changed to the stock covers and put a new pvc valve. It help the smell I was getting from the exhaust. I pulled my camper last weekend about an hour away. I pulled my camper about 4 hours back in the summer. It runs very strong. The plugs looked fine I checked them a few weeks ago. Is there a way to check the intake?

[390owner]

The machine shop built me a 390 about 20 years ago. I never had any problems out of it. I had about 120000 miles on it and it started using oil bad/ The rings were bad. So I had him build me another one but the oil issue now.

[Drew Pojedinec]

Pull the plugs. If just one or two is fouled the story is told.

[chris401]

Pull the plugs. If just one or two is fouled the story is told.

Good advice. If the oil shows up on all or not at all you maybe winding the engine high enough to pickup oil through the PCV. Running 70 mph my truck with 4.10's burns 1/2 a quart every 600 miles. About 1 quart if I run 80-85 mph on the same trip.