Oil Consumption / Burn

Hi, I have a 96 corolla with 335,000 KM and its had a considerable amount of oil consumption lately (about 1 litre every 500km). It doesn't smoke at a cold startup, only when you coast down a hill and start off again at the bottom. It'll leave a big cloud of blue smoke. The engine still sounds smooth and it gets good mileage.

I checked the PC valve by giving it a shake and I could hear it rattle. It has never been replaced and since it is inexpensive maybe I'll change it anyway. I have no check engine light since I replaced my rear O2 sensor. The car has been maintained well and I have changed the oil every 5000Km with Castrol GTX 5W30.

If anyone has any areas I might look next that would be great! Thanks

Reply to
BPC
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: I have a 96 corolla with 335,000 KM and its had a considerable amount : of oil consumption lately (about 1 litre every 500km). It doesn't : smoke at a cold startup, only when you coast down a hill and start off : again at the bottom. It'll leave a big cloud of blue smoke. The : engine still sounds smooth and it gets good mileage. : : I checked the PC valve by giving it a shake and I could hear it rattle. : It has never been replaced and since it is inexpensive maybe I'll : change it anyway. I have no check engine light since I replaced my : rear O2 sensor. The car has been maintained well and I have changed : the oil every 5000Km with Castrol GTX 5W30. : : If anyone has any areas I might look next that would be great! Thanks

Valve guides.

Mack

Reply to
M. MacDonald

PCV system

Reply to
Ray O

Why the PCV system?

Reply to
Philip

Just because you can rattle the PCV valve and hear the ball/slug moving freely inside it, that does NOT mean that it (or the rest of the PCV system plumbing) is clear and working, though it _is_ the most likely place to start.

I'd physically flush the PCV valve out with solvent, then make sure the intake and exhaust plumbing is all clear and clean. Any kinked, clogged or collapsed hoses, blocked valve cover ports or clogged filters will mess things up just as badly as a stuck check valve.

I'll bet that valve guide seals won't flush through that much oil around them while running without also giving him the characteristic big start-up smoke cloud also.

The OP's note of the smoke getting bad on over-run or high manifold vacuum conditions makes me think oil rings. If it is coming from the valve stem seals, there may be a return gallery restriction in the head (Sludge?) and oil pooling at the valve guides - they aren't made to deal with being at the bottom of a lake.

BPC: Have you checked the sparkplugs to see if one is getting oil fouled? Done a compression/leakdown check? Done a "wet" compression test (squirt in some oil) to see if it gets any better?

If a cylinder's compression reading gets a lot better on the second test with a squirt of motor oil into the spark plug hole, chances are the piston rings are probably shot. With that mileage, if the proper periodic maintenance (oil changes, etc.) was not done by the previous owner(s), worn piston rings are possible.

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Reply to
Bruce L. Bergman

No smoke at startup would make valve guides less likely. I'd think that bad oil rings would cause some smoke when revving the engine, not just after a long coast. Coasting down a hill creates high intake vacuum, possibly drawing oil through the PCV system somewhere, then back on the gas burns what was sucked through creating the clouds of smoke.

Agree? Disagree?

Reply to
Ray O

1) Coasting down hill does create high manifold vacuum. The condition does reach the intake valve guide seals and to a lesser degree (due to the compression rings), the oil rings but ONLY while the piston is moving down on the intake stroke. 2) When there is high (above 15" of intake manifold vacuum), the PCV pintle valve is pulled up tightly against its spring which results in minimum air flow. So ... unless the PCV is already being flooded with oil, simply coasting down a hill is not going to result in oil smoke out the exhaust pipe. 3) If for any reason the intake guide seals or the rings are being overwhelmed with oil, things such as oil pooling around the guide seals, cooked guide seals, and ring/cylinder wall damage from overheating need to be considered.
Reply to
Philip

Thanks for all the posts...I wish I had some good news. I replaced the PCV valve and inspected to hose for blockages, and there were none. I also took a look at that return hose beside it and it was clear also. I'm still having the same results though unfortunately :(

I haven't inspected the plugs since I changed them a few months ago, nor have I had a compression test done. I should look into it.

I wish I knew why this is all starting to happen. I mean I know everything wears out, it's just I've owned this car since it had 45,000 kms on it (Dec 99) and I never skipped and oil change. I thought I'd get a little more before the engine was this far gone. Maybe the type of driving I do has been more demanding on it. I do a 50/50 highway/stop and go driving, with well over 100 stops a day (I deliver newspapers).

Something else that might be worth mentioning, is that the car will ping (forgive my ignorance if this is an incorrect term) or maybe it's the lifters at lower speeds. The most noticeable time this happens is usually 2nd accerating up to 3rd (at a light to med throttle). It doesn't matter which grade of gas I burn either, and it's not there at highway speeds.

Maybe it's just tired of delivering papers! ;)

Reply to
BPC

AH.... now we have another variable. ANYTIME you have preignition (ignition before the spark) or detonation (secondary ignition occuring after the spark), you will subject the piston to sonic shocks (the 'pinging' "cheap gas" sound on acceleration) which in turn disrupts all the rings ability to seal both compression and oil while the knocking is audible. An occasional light spark knock is not detrimental. But if it is a long time chronic occurance, engine damage does result.

What things typically contribute to preignition and detonation? Depends on the engine's age/condition. Very low octane fuel, ignition timing set too advanced from factory setting, a non functioning EGR system, other faulty emission control components controlled by the engine ECM, gross carbon deposits in the combustion chamber.

Reply to
Philip

I would have to venture a guess at the reason for my pinging would be incorrect ignition timing. Philip, how does the ignition timing go off of what it should be and could this happen when a timing belt is installed? The reason I ask this is it seems to me that this pinging started to occur around the time I had my belt changed last. It is probably a rediculous question but I had to ask (I'm not very knowledgeable about this stuff). Is the timing set in the distributor somewhere and is it a very big job to adjust? Thanks for the help!

Reply to
BPC

Toyotas have 3 basic systems for ignition systems.

1) The traditional coil-distributor-spark plug system. Base timing is set by loosening a bolt at the base of the distributor and turning the distributor. Ignition timing is advanced at higher RPM by means of a centrifugal weight and/or a vacuum advance. 2) Traditional coil-distributor-spark plug with electronic spark advance. Base timing is set the same as the original system but the rotor has a much wider arc and timing is adjusted electronically in conjunction with knock sensors that detect pinging. With electronic spark advance, the knock sensor should detect pinging or knocking within 3 pings or knocks and retard ignition timing. 3) Distributor-less ignition. Each spark plug or pair or spark plugs has its own coil and are commanded to fire by the computer. Base and advanced timing is controlled by the crankshaft position sensor and the computer.

It is possible that the camshaft timing is off by a tooth but you generally get poor performance all the time. It is possible that the distributor was disturbed when the timing belt was replaced although it is not usually necessary.

Reply to
Ray O

On engines with a distributor that has an ignition trigger on the distributor shaft, all you have to do is rotate the distributor housing in order to alter ignition timing. ABSOLUTELY, ignition timing on an engine with the timing trigger inside a cam driven distributor can be altered when the cam belt is changed.

Ignition timing procedure is outlined on the EPA sticker, typically located on the underside of the hood. A jumper wire between two terminals is usually required so that the ECM is forced to 'base timing' for adjusting. A timing light is required.

Reply to
Philip

I appreciate all the help guys - very informative! I got an appointment at Toyota on Wednesday to get the timing checked. I sure hope they can get to the bottom of things.

One other thing I am wondering is can there be something wrong with the EGR system without a fault code being set off? Would it be worth a look to see if it's working ok too?

Reply to
BPC

Whether a problem with the EGR system will set a fault code or not depends on the fault detection system. An OBD II system will probably detect a fault; an earlier system probably will not.

In any event, an EGR problem will not contribute to oil consumption.

Reply to
Ray O

Ah ... here comes the descenting opinion. When ignition timing is optimized for the presence of substantial amounts of EGR (which permits upwards of 4-8 degrees MORE timing than without EGR), the absence of EGR for whatever reason will result in detonation / spark knock. This phenomenon was VERY apparent in older vehicles having no engine knock sensor circuitry. The sonic and physical shocks imparted to the piston will disrupt the oil rings ability to seal out oil while the shock treatment is occurring. During severe knocking under load, light blue exhaust smoke can be visible to the driver -following- the afflicted vehicle.

Reply to
Philip

There is a flaw in your logic, when EGR is flowing more spark can be used because it dulutes mixes and slows combustion and reduces peak temps to reduce NOx formation. (more spark is need to try to burn this mess) EGR is not a MPG maker and it does reduce power output and responce too. The reason that older cars knock more is because they really need more than 87 octane to do their best but most are to cheap to buy it so they detune engine to run on 87 and loose power in process. Make no mistake that when you run 87 in a modern V8 and the spark knock retard is active to contol knock you are loosing power and MPG plain and simple.

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Reply to
TheSnoMan

There is no 'flaw in the logic.' I cite an observable phenomenon from days when I was a state certified smog mechanic. All such shops in CA had to have a dyno which is how I came aware of the phenomenon.

You are started out correctly until .... you say more spark is needed. That is not correct. The correct nomenclature would state more spark lead time is allowable with EGR functioning. Also, I made no reference to EGR increasing MPG. That is an entirely different discussion.

This is a half truth. Did you miss the portion of my statement noting that disabling EGR on an engine that has knock sensor circuitry will result in less or no audible knock BECAUSE the ECM will retard ignition timing to compensate for the EGR absence?

I won't make the economics assertion that you have. And I can CERTAINLY argue your faulty assertion that using lower octane fuel results in lower fuel mileage. There are less BTUs in higher octane fuel than lower octane. When ignition timing is optimized for 87 octane but then you substitute 93 octane, fuel mileage decreases simply because there are less BTUs in Premium. That the ECM may "adjust" for this fact is the reason most engines do not experience a drop in MPG when substituting Premium for Regular. May I recommend you read some SAE papers on the subject.

-Philip

Reply to
Philip

I inspected the spark plugs and one of them had some oil around the threads and the boot from the wire had a little condensation / oil on the bottom. The rest of the plugs were dry (the threads were just brown in color but not wet) and the boots were dry too. Also, one of the other plugs seemed to have half of the casing (not sure what to call it) missing around the centre wire. I switched it with another one, just to be safe...I've never seen that happen before. I only use Nippondenso's and these plugs are only 5 or 6 months old.

Something else I've observed when driving is that the car seems to work best before it reaches normal operating temp (no ping/knock or smoke). Would that signify a problem with one of the emissions systems or something controlled by the computer? I don't know what the compression is like but I know the car still runs great, except at the moments it smokes when you start off after a coast.

Reply to
BPC

Many years ago when I actually studied this in college, it was written in the text books that higher octane fuel had less energy per gallon than lower octane fuel. However, I don't believe this is the case today. I've researched the subject and can't find any recent refences that support this idea for modern fuels.

From

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"Power

".....Because different grades of gasoline have essentially the same heating value, they all provide the same power in a given engine as long as their antiknock performance meets the engine's requirement...."

"Fuel Economy

".....Conventional fuels always have varied in heating value. One cause is the formulation differences among batches and among refiners. A survey of

1990-1991 conventional gasolines found that the heating value of summer gasolines varied over an 8 percent range.

".....The heating value also varies by grade and by season. On average, the heating value of premium-grade gasoline is about 0.7 percent higher than regular-grade because premium-grade, in general, contains more aromatic hydrocarbons - the class of hydrocarbons with the highest densities. The heating value of winter gasoline is about 1.5 percent lower than summer gasoline because winter gasoline contains more volatile, less dense hydrocarbons."

From

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: "Gasolines with higher heating values give better fuel economy than those with lower heating values. There is generally only a small difference, about

2%, between premium and regular gasoline. This difference traditionally favo urs premium gasoline but it can be in either direction."

I owned a 1997 Expedition with the 5.4L V-8. When this vehicle was introduced, Ford told the press that if poremium fule was used instead of regular, the engine would provide slightly more power (5-10 hp) and slightly better fuel economy. After reading this I experimented with premium fuel. I never could detect any difference in power (but I never did timed acceleration runs) or fuel economy when running premium either up or down (depsite using premium for 20,000 miles and forcing a PCM reset).

Ed

Reply to
C. E. White

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Ed: In California (in particular) the primary way forumulating Premium fuel is to have more oxygenates in the formulation which lowers the BTU per gallon. This is born out in the information you cite above and in the "Factors Affecting Fuel Economy" section of your first link.

To wit: "The gasolines used in the Wisconsin test were commercial gasolines - a conventional gasoline and federal reformulated gasolines (federal RFGs) oxygenated with MTBE, ETBE or ethanol. When the results for all the road tests of all the vehicles were combined, the average fuel economy of the three oxygenated federal RFG gasolines was 2.8 percent lower than the average fuel economy of the conventional gasoline - a value much less than the 10 percent week-to-week difference for some of the car-fuel combinations, but right in the range predicted by the differences in the gasolines' heating values. "

So I take the position that "gasoline" has a given BTU per gallon but ... what makes it Premium grade results in lower BTUs. :^)

Regarding your Ford, stop and think for a minute. The sophisticated OBD-II class ECUs will compensate for octane by adjusting the ignition timing and EGR curves to always achieve a tiny amount of spark knock which may not be audible to you but to the ECU. Were this not the case, your fuel mileage would drop when running a lower octane fuel and possibly exhibit spark knocking if the timing was optimzed for the higher octane.

Reply to
Philip

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