Oil consumption goes down for while after change - why?

[movin]

My '87 seems to consume very little oil right after an oil change, maybe 650mi/quart. But, after a 1000mi+ it begins to consume more about, 450mi/quart, and smoke at startup. I usually let it go for about 3,000mi then change it, then the smoking at startup goes away and consumption goes down again. The engine has 124,000mi and it's been doing this for about the last 15,000mi. Any ideas what's up? Could unburned fuel contaminate the oil causing it to be consumed more readily? It seems to run fine, doesn't run rough like it's miss-firing. Could slight ignition wire leakage degrade the combustion process and not be felt as miss-firing?

[AFJuvat]

While your numbers are a little "high", your oil consumption does still fall within specifications.

You didn't specify what kind or weight of oil you use bus assuming you are using dino juice:

It is possible that the oil is starting to lose some of its viscosity letting it flow through slightly worn valve guides

Now would be a good time for a compression test or a leak down test. It would be interesting to see if you got different numbers right after an oil change and then 1000 - 1500 miles later.

AFJuvat

[Zeke]

Yeh, what kind of oil are you using?

[RoninLB]

gas can be tested in an oil analysis, among other things.

I've done a few as a kinda scan.
I use the rennlist e-mail guy called Larry Turner. Maybe $20 for a single test. I've done the 3 pack upon occasion.
Widebody had a wild engine problem that made him nuts till the oil analysis gave him info.

and I think there's some speculation than the 3.2 valve guide problem is injector related.

[movin]

Ronin,
You mean the injectors may be the cause of some of the Carrera series valve guide wear problems? I didn't think of that, poor atomization or excessive fuel charge? but wouldn't the O2 sensor see that and correct it, (well if it was within its limits to)? BTW, I'm using Kendall 20W-50.

[Bill Douglas]

It's probably because you oil is bvecoming contaminated (with petrol?) and is thinning out and gets past your valve guides and rings into the cylinders. When it's nice and fresh it's a bit thicker and doesn't get in so easily.

[RoninLB]

Originally posted by movin
Ronin,
You mean the injectors may be the cause of some of the Carrera series valve guide wear problems?

I didn't think of that, poor atomization or excessive fuel charge?

but wouldn't the O2 sensor see that and correct it, (well if it was within its limits to)?

I don't have hard speculation info because I don't have a 3.2. but

it's said that it's excessive fuel.

I don't know much about the O2 sensor's little quirks.

But I would do an oil analysis as part of routine matainence if I had a 3.2 ..........Ron

[Early_S_Man]

movin,

I don't know where the injector 'theory' came from, but if a 3.2 is still getting great gas mileage, then you can throw the injector theory out the window!!! Enough excess gasoline to thin your oil would show up in consumption figures. Excess gas from a leaking injector, for example, would show up on your spark plugs as black soot deposit, and in poor gas mileage. Sometimes a bad oxygen sensor shows up as poor gas mileage because the DME stays in default 'limp mode' which is a rich fuel map.

Most experts say that excessive valve guide wear on 3.2s had been traced to the switch to the orange/brown elastomer valve stem seals, and that using the white Teflon seals on a top-end job will eliminate the problem. With the orange seals, oil to lubricate the valve stems is severely reduced compared to the previous Teflon valve stem seals, ans excess wear of the intake valve guides is the result.

Oil smoke on startup has nothing to do with worn valve guides ... since many cars do it, regularly, from day 1. It is not a problem if the smoke cloud disappears in a few seconds. It can be related to the angle your car is on when parked overnight!

My suggestion is to pull your spark plugs and look for abnormal signs. Your oil consumption figures are not excessive.

[targa911man]

I think there are friction-reducing components of the oil that burn off at the operating temp and maybe even a little lower. The more they're burned off, friction and heat increase, so the rate of burnoff increases. Remember the oil is also cooling, not merely lubricating your engine. So it is absorbing heat from the engine. The less oil there is to absorb heat, the hotter the oil that's left will get. Sometimes, when an engine tends to run cool or it is simply not driven hard, the low-temp components burn off right away, so it looks like your down a quart or so right away after an oil change, then it stays level for a while because what's left has a higher temperature tolerance. This is not just my theory, I read it somewhere, maybe in Excellence or here.

[Wil Ferch]

I've heard Early-S-Man's type comments before....newer seals are too good and starve valve stems from proper lubrication, causing wear.

Hmm... let's look more closely at this.

Seals are too good...poor lubrication...causes wear on valve stems... BUT...before we get "too much" wear...wouldn't it be rational to expect that as the stems wear a small amount at first, we re-introduce proper lubrication past partially worn stems....and this now stabilizes and pretty much stays that way ?????

---Wil Ferch

[movin]

Let me add that I've always smelled burning oil in the exhaust for over the last 35,000mi, but see only an occassional faint blue emission during driving.

[RoninLB]

Originally posted by RoninLB
gas can be tested in an oil analysis, among other things.


and I think there's some speculation than the 3.2 valve guide problem is injector related.

from Excellence

[toolman]

Your lucky you don't have a worse oil usage problem at that mileage. My 87 only had 77,000 and was using a quart every 125 miles. It was the valve guides, they were completely wore out.