Why does oil burn off happen to me deep into OCI?

[Jaymus]

Well, on my wife's 2001 Eclipse GS 2.4 SOHC 4 cyl with 179,000 miles, I have noticed one thing.

I use RTS 5W-40, have for a couple of years. After 1500-1800 miles, the oil doesn't move down a DROP. Then it starts dropping... it eventually gets to using a quart every 1000 miles around the 3000-4000 mile mark in the OCI, then a quart every 300-500 miles every 500 miles.

Change the oil, not a drop used for 1500 miles again.

What causes this in an engine. Remember I'm even using a thicker oil, RTS 5W-40. And I always top it back off with fresh oil. It doesn't smoke at all, no coolant goes in to the block. Motor runs fine, just has high mileage and we didn't get it from the best maintenance person, but we've done religious oil changes from 125k miles to nearly 180k miles.

Anyways, what causes that burn off to happen as the mileage gets higher, even when adding a quart every 500-1000 miles.

It goes like this:
up to 1500 miles - no oil used
2000 miles - maybe 1/4 quart used
2500 miles - whole quart used, I then top off
3200 - 3800 miles - another whole quart used... I then top off
It uses another quart by 5k miles, and I usually just change the oil by then.

But why doesn't it use ANY, not a drop to the eye, by 1500 miles?

 

[JAG]

Fuel dilution comes to mind.

 

[Jaymus]

It definitely is an engine that runs rich. All these Eclipses with this engine were known to run rich. You do smell fuel in the oil. I've begged my wife to get a tuner, so she'd save gas and gain more power and mileage, because they are known to run rich.

Think that's what's causing it, and would a tuner to lean it out solve or help fix the problem?

 

[daman]

Fuel dilution i'd say also,,UOA it and see.

that's allot oil!

 

[JAG]

It's as good a guess as I can come up with. I don't think that it's due to piston ring deposits building up, leading to excess reverse blow-by and therefore oil consumption because the miles on the oil are so low.

If the tuner will help gas mileage too, you will save on fuel and possibly oil cost through less top-offs. Balance that against the price of the tuner.

 

[Jaymus]

Yeah, it gets 30-32mpg on average (after putting Redline MT90 in tranny and synthetic in engine, up from 27mpg).

I don't think the fuel dilution is bad enough to make the fuel mileage bad, although mileage is AWFUL driving low RPM on backroads, while gas mileage is AMAZING driving 3000RPM down the highway.

I think a tuner would help keep the fuel out of the gas and give more performance, while increasing city mpg.

EDIT: But if this is what you guys think is going on, that's good to know. It's something that can be easily fixed (a better tune). I have been dying of curiosity about why the oil doesn't get used at all until 1500miles, then boom, it starts eating it... but NEVER blows blue smoke. Not even if idling for 10 minutes then you rev it. Not on a cold start in the morning (or warm start after leaving a store). Never puts out blue smoke.

 

[Jaymus]

And, yes, I should do a UOA. I would have liked to have done a UOA on the last OCI. 9100 miles on RTS 5W-40, but probably 4 quarts of make-up oil, so the UOA wouldn't really be accurate on wear or TBN, but it would give me a good idea on fuel dilution. Just that times are rough around here, hence the long OCI (which is probably actually fine with this oil + amount of make-up oil I added). I saw a 10k OCI on this engine here a few months ago with excellent results. These engines are very easy on oil.

 

[Gene K]

Ive seen the same thing in Diesel Engines. My best guess is something is reducing ring seal (insolubles?). Thats despite excellent Soot, Fuel, TBN, TAN, Viscosity, Insolubles, Oxid, Nitr.

However its not as drastic as what you are seeing in your case. It may be fuel dilution masking initial loss and thinning oil which increases additional loss.

If it turns out not to be excess fuel dilution I might just add a quart every 750 miles and change the filter every 10,000 miles and call it done.

 

[mechtech2]

I had a BMW 320i that did this.
No oil consumption to speak of , until 2,000 miles.
Then she would start to use it.
I think oil shearing was the main reason -maybe some odd additive depletion ensued then.

 

[Spykem4e]

My 05 CTS is doing the same thing.
Its taking 1/4 qt for the first 2000 kms.
Then, 1/2 per 2000 kms.

 

[steve20]

had the same issue with my 92 Camry 4cyl-no usage until 2K then used a quart between 2K and the 5K oil change 160K when I sold it

Steve

 

[Gary Allan]

Quote:
And, yes, I should do a UOA. I would have liked to have done a UOA on the last OCI. 9100 miles on RTS 5W-40, but probably 4 quarts of make-up oil, so the UOA wouldn't really be accurate on wear or TBN, but it would give me a good idea on fuel dilution.


Do the UOA at the first full quart of consumption; the point where it uses it every 1000 miles before you top up. That will eliminate the make up component from the sump. You appear to report the consumption as being linear from that point out. I'll speculate that you're adding just enough new oil to maintain the 1000 mile consumption rate.

What would be a good experiment (understanding that you're not in a position to be playing around at this time) would be for you to dump the sump at the first point of this routine consumption ..and save it. You would than use this oil for make up on the next sump and add it as you would new oil. It should be the same age as the current sump. If the consumption stayed flat, then the make up oil isn't doing anything at restoring some depleted component. If it increases, then the new make up oil is maintaining some level of (whatever) is keeping it to 1000 miles. Ideally, I'd test both the 1500 old sump ..and at the point where the second sump bottoms out (or you've used up all the old 1500 mile old make up).

That probably communicated what I was trying to say poorly.

It could simply be viscosity, but that's got to be one vicious engine condition to pull such a beat down on RTS.

 

[javacontour]

I experienced the same with my 1994 Geo Prizm with 254K miles on the clock. Consumption was not linear, but increased as the oil aged. I ran 5K OCIs at the end, and I probably would have used the same amount of oil had I just replaced the oil at 3K intervals.

The first 2000-2500 miles it might consume a quart, and then consumed another 1 to 1.5qts over the next 2-3K miles. I know it was leaking some, but that would be close to linear. Ditto for burning. I suspect the cam drive was shearing down the oil. Only one camshaft was driven by the timing belt. The other was driven by a gear from the first camshaft. It's believed that this arrangement does a number on the oil, shearing it down more than other arrangements. When you combine this with the existing leaks and age of the engine, that sheared down oil is probably easier to burn, to leak and perhaps even easier to vaporize, getting into the combustion chamber via the PCV system.

I found it easier to park over a box of kitty litter and add $2/quart oil than to do any real work on the engine.

Getting UOAs on the oil at 1K intervals BEFORE any makeup oil is added would be some interesting science, similar to the Spacebears study of Mobil 1 over a long interval in their GM V8.