Question : Oil Disappearing Mystery -- Burning really?

[Jesuscookies]

I have a 1994 Olds Cutlass Supreme, 3.1 Vin M recently purchased, that was in need of a little TlC.

The car currently only has 28K miles. I did the intake manifold gaskets, replaced the radiator, AC, and a ton of other little things.

I finally get everything back together and change the oil. Check it after the first week, and I am missing about 1/4 a quart. Fill it and check it again the next week missing about 1/4 of a quart.

The driveway floor is dry, and I can see no leaks. The distributor plug thingie is dry so it does not appear to be an external leak. I have dye in the oil, and have been looking all around but still nothing.

Is there anywhere else this engine could be leaking oil? Internally or externally, that I am missing?

Can an engine with only 28K miles be burning 1 qt of oil per 1k miles? is this normal?

I hope I am missing something.. Any help or advice is greatly appreciated.

[bszopi]

Are you noticing any color smoke out the exhaust, more a typical car? On a car that old with that few miles, I just wonder if there may be an issue with the rings not sealing well anymore. You wouldn't think so, but you never know.

[robertisaar]

28K miles on a 17 year old engine?

i have to wonder if the rings are causing this.

[Wallace]

I'm betting the valve seals are toasted. Have someone follow you around while you drive the car to see when it smokes. On decel and idling if it smokes it is probably the valve seals.

[Jesuscookies]

Are you noticing any color smoke out the exhaust, more a typical car? On a car that old with that few miles, I just wonder if there may be an issue with the rings not sealing well anymore. You wouldn't think so, but you never know.

No not really, although I have not paid super close attention to the exhaust. I will now though. I would imagine it would be a good amount of smoke if it was burning that much oil?

I'm betting the valve seals are toasted. Have someone follow you around while you drive the car to see when it smokes. On decel and idling if it smokes it is probably the valve seals.

I will try this, mechanic friend suggested valve seals as well. Should I be seeing a lot of smoke or just small traces?

Also, in both of these cases, valve seals and piston rings, is a full rebuild required considering the car only has 28K otherwise? Could I do this myself with engine still in car?

Thanks for all the help...

[Wallace]

I believe you can do the valve stem seals in the car....the rear cylinder might be a bit of a challenge. I've never done seals on a v6 in a FWD app with it still in the car..hopefully someone else will chime in with details on whether you can do it easily or not. Smoke should be noticeable. You can do a compression test as well to check the rings. Check with engine hot. Go back and add a small amount of oil to each cylinder and check again. If the readings are noticeably higher with the addition of the oil then your rings are worn. Good luck.

[robertisaar]

keep in mind the cat can mask some smoke by catalyzing it as it passes through, but it can only do so much.

[trotterlg]

10,000 miles a year will cost you $15.00 in oil, how many years worth of oil do you think changing the seals or rings will cost you? Larry

[pocket-rocket]

I agree with ^^^

Also, on the plus side of it your oil will run cleaner having to add new all the time... It's not leaking it, so it's not contaminating the ground. Personally, I would check the plugs a couple times a year, keep a close eye on the oil level and run it. If it starts getting sluggish and the compression tests come back ok, spend a small chunk of change on a new cat on ebay.

[Jesuscookies]

Digging into the engine is the last thing I want to do. When I changed the intake manifold gaskets, I also changed the spark plugs. They showed completely normal wear with no signs of burning oil. This leads me to believe that something else may be causing the problem. I also changed the valve covers (upgraded to aluminium) when I did this job. The valve cover had a PCV valve that was riveted in so I did not change it, but I'm wondering if this used PCV valve, from a different engine, could be causing the problem. E.G. sucking oil instead of air?

Last night, I cut the rivets off and replaced the used PCV valve with the original from my engine. I'm hoping this was the problem. However, if this does not fix it, I will put a treatment of auto rx into the engine and live with it for the time being. Time will tell

[robertisaar]

if you take the intake tubing off and open the TB manually, with a flashlight you should be able to tell if there is any oil built up in the UIM.

[pocket-rocket]

Isn't the riveted in PVC valve covers from the 3500? Wasn't jmgtp having a bunch of oil show up in his TB on his 3500 swapped GTP?

[geldartb]

Isn't the riveted in PVC valve covers from the 3500? Wasn't jmgtp having a bunch of oil show up in his TB on his 3500 swapped GTP?

the newer 3400's had a little bracket riveted as a hold down sort of but nothing a hacksaw couldn't get rid of. the 3500's i saw it was more or less part of the valve cover.

[Jesuscookies]

the newer 3400's had a little bracket riveted as a hold down sort of but nothing a hacksaw couldn't get rid of. the 3500's i saw it was more or less part of the valve cover.

Yeah, this is the way my replacement valve covers arrived. I did read on here that someone else had a similar problem. I do not think the 2 PCV valves are compatible. Anyway, took an air saw to it, and removed the bracket. I put in my old PCV valve. So far I have driven 50 miles with no oil loss, but will need another few hundred miles to be sure. I also removed the intake hose, and put my UV light into the throttle body. There does appear to be some small glowing remements from the dye I put in. I'm about 95% sure this is the problem, but will drive it for another week and measure the oil to be sure.

I will be so F!@#$%^ thrilled if this is the problem!

I wonder what the difference is between the 2 PCV valves, and why GM made this particular setup non-serviceable (kinda )?

[Jesuscookies]

Okay put another 150 miles on the engine with the original PCV valve, and (HOORAY!) no oil burn. Looks like the PCV valve was the culprit.

Does anybody know what the difference between the 2 valves are, or what could have caused the one from the 3400 to suck up oil?