gringodon.com

I have a 2002 GT 4.6L manual 5-speed with 323K miles on it. Original stock engine. Runs great, very good gas mileage, but I’m adding 1 gt oil (Mobil 1) every 800 miles. My mechanic has run a compression test and leak down test. He told me rings still in good shape but I’m leaking oil down the valves. No external engine leaks found. I have no smoke out the back, not at start up, not sitting at an idle, not running, and not accelerating. Can anybody tell me when or at what oil consumption level I would expect to see the dreaded blue smoke out the tail pipe? Does this even make sense?

Past repairs are - both forward O2 sensors replaced, one clutch at 140K, plastic intake replaced with aluminum and normal general maintenance.

Have always run Goodyear tripletred tires, get 100K per set, I’m on my 3rd set. I drive 120 miles round trip a day to work, through snow and ice in winter. This car flies, even on ice. (Not that any of this info matters to my question) Best car I’ve ever owned.

DeathRattle

So you're losing a quart of oil that often, and you're losing that much down the valves into the combustion chamber, but you're not getting any smoke at any time? My old 95 T-Bird lost nowhere near that much oil and it smoked heavily after being stopped at a light or stop sign. How is your oil pressure at a dead stop? And are you sure you're not losing oil somewhere else? Because if you're losing a quart into the combustion chamber, you'd be seeing and smelling smoke.

gringodon.com

I look into the rear view mirror when starting off from a light, no smoke. Stand behind the car and let it idle in the drive way, no smoke or smell of oil. Start it up cold, look in the rear view mirror, no smoke. Oil pressure gauge rides just above half driving or at idle. That's why I was confused. I'm not a heavy car guy but I thought I should be smelling or seeing smoke at this stage. I have had the car looked at by two different shops for oil leaks and none could find any. Now I'm even more confused.

Weather Man

My durango used that much with no smoke. The cats were evidently able to burn it up. Time for a valve job though, or some cheap lower mileage takeoffs.

gringodon.com

If the cats are burning it off, am I in danger of plugging up the cats? This has been going on for 6 months range.

Weather Man

The cat(s) will eventually fail and check engine light.

DeathRattle

A catalytic converter will not soak that much oil into it and not give off smoke. Even if they did, have you seen how hot they get? Surely there would be some smoke. Cats are designed to convert toxic pollutants and make them less toxic. If that much oil was going through it, then the oil would have coated the substrates inside the cat until eventually the cat would no longer be able to function at all. Then you'd be getting fuel fumes, oil fumes, and smoke out the tail pipes. If it were a small amount of oil then I could see maybe. But I doubt it. Like I said, I had a T-Bird that had pretty bad valve seals or possibly bad oil rings. I didn't lose anywhere near as much oil as you and my car smoked quite a bit. That oil is going somewhere. Have you checked under the car for oil leaks while the car is running? Have you checked your PCV valves recently? Also check your crankshaft seal and your rear main seal. But I can pretty much assure you that if as much oil as you say is going through the combustion chamber, you'd be getting at least some small amount of smoke.

JC316

Prime indicators of the valves leaking down is a huge puff of blue smoke when you first start it in the morning. Even if the cats could burn that off, there is no way they would do it cold.

If there is no smoke, that oil has to be going elsewhere, that or it has smokeless oil in it. Might be your PCV system sucking in enough to burn, but not enough to show smoke, but I highly doubt it's the valves.

gringodon.com

Ok, so what I gather from this is, (please correct me if I am wrong) if I am burning a gt of oil every 800 miles, then I should be seeing smoke at some time out the tail. And it seems logical that after the car sets all night and is then started up in the morning. Oil that has slid down the valve stems during the night should come out the tail at startup as smoke. Being that the cat cannot do its job until it is up to temp. So the smoke would just pass through the cat (at least at start up). But one would also have to ask - that after over 300K on the car, could the valve seals not be leaking at least a little?
So this amount of oil or a large portion of it has to be going somewhere else. The PCV valve has been replaced once, about 50K ago. Not that it was causing trouble; I just had it replaced as general maintenance.

Now as a side note – When a car starts to burn oil be it from rings or valves, would the O2 sensors pick that up as rich? and lean out the mixture? So I should maybe see the fuel trims riding on the negative side? No?

Once again I only know cars to the point that I can get into trouble.

JC316

Pretty much, yeah. The modular family is crazy tough, I had a 276K mile 01 expedition and it didn't use a drop of oil. It's possible for it to start wearing down, but I wouldn't bank on it just because of the mileage.

Yes, you should see the O2 sensors react to the oil and start dropping the trims into the -%. What brand of PCV valve did you get? I would double check it just to be safe.