Blue smoke on start for 3+ minutes
 

I have a 351 that I did not build. It has 3900 miles. The receipts indicate high end parts were used and the engine makes plenty of power, and has good drivability. I think it was built in a guys garage; not a shop.

The problem is, it uses about 1 quart of oil per 1000 miles and has blue smoke on start. The smoke will continue for a few minutes. If the engine is warm no smoke. No smoke is apparent when driving and the side pipes show no indication of oil useage.

I am leaning towards valve seals, but have never seen one use this much oil or smoke more than a puff. It has Edlebrock heads that were purchased for the build.

What do you guys think?

John

Do you get any smoke if you back off the throttle at about 4000 RPM and let it brake itself? If so, worn or leaky valve guides.

The other possibility, and one more likely, is the rings didn't seat properly and the oil is blowing by them into the cylinder.

Either one sucks!

My first guess would be valve seals. Once the motor is shut down, if there are bad/damaged, they would leak a little oil down the valves and upon start-up later you would see the smoke your talking about, but 3+ minutes seems a long time to me......

Were the Edlebrock heads used on the motor new or used????

Another thing might be a leaky intake gasket. A cold engine would suck a little oil till the engine warms up and things swell up, the leak could "seal itself".....

I'd start it up and let it run till the smoke stops then pull all the plugs and have a look see, this could tell you more about the oil burning.....

A quart evry 1000 miles after 3900 miles is too much IMHO........

David

It smokes for several minutes on first start. I estimate it to be 3-4 minutes which seems really long for valve guides/seals. It is not a puff of smoke like you used to see on high mileage Chev small blocks.

The heads were new, if the receipts are correct.

I pulled all the spark plugs earlier in the summer. They showed some oil useage, but not much and they all looked the same.

If you let off the throttle at high rpm there is no sign of smoke.

There is no indication of blow by in the PVC or crankcase vent. Both are dry.

The only time I ever see anything is on a cold start.

Keep the advice comming I may do more diagnosis this weekend.

John

I'd do a leakdown and a pressure test.

Back in the early 90's during my dirt track days we left the valve seals off on purpose to get a little extra lube on the top end of the motor... upon start-up, we would get one good puff of blue smoke that never lasted more than 30 seconds......similar thing happened with my road race motor last year, in a hurry to re-assemble it, found they sent me the wrong valve seals, so I put it together without the seals, smoke never lasted more than 30 seconds and wasn't all that much to begin with......after that you didn't see any smoke during normal running nor racing.... Oil consumption was very little, not enough to worry about bewteen changes, probably less than 1/2 quart.........

3+ minutes is too long and would suggest something else as the problem as would all the plugs looking the same with some oil useage on all of them....

Next guess would be PCV or possibly some oil coming from poorly baffled valve cover PCV and/or breather?????

Defintely should be your next step.........also try running it with the PCV removed....try the easy and simple things first....

It's sucking oil from somewhere and with the plugs all looking about the same,that would point to getting oil into the intake and going into all cylinders.
I'm kinda stumped with this one, if the rings didn't seat, you should see some blue smoke pretty much all the time, and using a quart of oil every 1000 miles would make it smoke more than just 3 minutes after start up....

David

Are you using a PCV valve? If so, disconnect the hose and see if oil runs out. I was burning 1 qt of oil every 300 miles or so through the PCV valve!

I do run a PVC. It is dry, but I will disconnect and run for a while. Next, I will check compression and leak down.

This one has me stumped.

John

My '02 Z06 burns about a quart every 1K miles or so. Every 'Vette forum that I've been on says it's not unusual for the LS6 to do this. I never have blue smoke gurgling out of my exhaust. Am I concerned about it? Given the specs on this particular motor, the track record from other owners, the non-existence of blue vapors and the fact that I bought an extended warranty, no.

But I'd still like to know how a motor can burn that much oil without giving any indication visually that it's doing so. Also, no leaks either.:confused:

-Dean

Every Chevy that I have owned used to use up that first 1/2 to full quart and then stay that low until the oil change.

If it is not a torn/sucked up intake gasket you might want to pull the heads and have them checked for cracks.

Sounds like it could be a small crack in the head (hope not).

After the engine sets overnight, pull the plugs and get something like a q-tip (but longer) and stick it in the plug hole down to the piston. You can see just how much oil is sitting and which cylinder is the bad guy.

Terry

Dump the synthetic oil, run 20-50 wt dinosuar. It could be as simple as the wrong oil or contaiminated oil. Sometimes it's amazing what an oil change can do.

I agree. I run 30W in mine. That is what was around when these engines were designed. Synthetics in a newly rebuilt engine slow down the break-in period. Also, make sure the crankcase is not overfilled.

For what it's worth, when I worked for Ford, 1 quart of oil consumption per every 1,000 miles was considered normal on a car still under warranty.

GM sticks by the same mantra. Unless you get down to 500 miles or so, they won't even crack the hood.

Valve seal issues are typically limited to start-up and only a few seconds after that.

Mechaanical problems with rings, pistons, etc, usually don't go away with warm-up.

I'd suspect you have aleaky gasket that closes up tight once the engine warms up. Intake manifold gaskets are a natural "first look". Could also be a head gasket, but that's not as likely.

There's exceptions to all I wrote, but typically, I think I am correct.

1/ Althought intake gaskets can leak from the bottom (where the oil is), you can try squirting a little WD40 around the manifold and see what haappens.

2/ A compression check won't do much, but a leak-down test can tell a lot when it comes to leaks.