Oil burning, only downhill with closed throttle

[Hyrde]

I'd like to get some insight into this problem..

My Corolla 4wd 1.8 7afe burns oil whenever i go downhill in gear with my foot off the gas (engine deceleration), huge amounts of blue smoke. It takes a few seconds with WOT after downhill run to clear all the smoke.

If i open the throttle plate just a tiny, tiny bit or put the gearbox in neutral (it's a manual) and idle while going downhill i have no oil burning problems at all. It does not produce blue smoke under any other circumstances. Compression is 190 180 180 180 no change with/without oil in cylinder.

I think it sucks oil through the PCV system, due to the very high manifold vaccum at engine deceleration.
I've replaced the valve and checked the hoses but it doesn't help. There's a good amount of oil residue in the intake manifold.

Now the thing is, i just put in a "new" used engine.
I had exactly the same problem with my old engine with the blue smoke on downhill runs, except my old engine had no power and used way too much gas. The new engine is peppy and gets good MPG's. When i got the used engine the spark plugs looked good (slightly tan) for a healthy engine, but now there's quite a bit of black deposits on them.

The only common factor between the two engines is that I'm using the same kind of non-OEM oil filter. The PCV is also a non-OEM (AC Delco).

Why does it burn oil like this and what can i do to stop it. I've tried various engine oils and there's no difference. It does not consume any oil at all if I'm careful and always go idle downhill, but it's a chore and I live in a hilly place and MPG's do take a hit with all that idling downhill rather than engine braking where there's no gasoline used at all.

The only things left that I have not tried is an OEM oil filter and OEM PCV. Do you think this would even make a difference?

 

[FowVay]

Make sure there are no restrictions in the induction system. The engine needs to draw air from some source and if the designated source is blocked then it will draw from the next available source which would be the crankcase vent.

Since this has happened with two identical engines then search for the problem in something that did not get changed.

Off topic but I see this all the time with lawn mower engines. The air filter is completely clogged and the engine draws air from the crank vent. They usually deplete the oil supply in the process and burn up the engine.

 

[Hyrde]

The air filter has not changed. It looks good and i have sprayed it out with compressed air, but i guess you never really know with microscopic dust. It is a brilliant suggestion, i will try it. Thanks!

Edit: Well the throttle plate is a pretty good restriction though isn't it? And it only uses oil when it's fully closed. Maybe cleaning it would help too.

 

[Eddie]

High intake manifold vacume will draw oil passed weak picton rings & worn valve seals. Nothing will help this except replace worn parts IMO. Ed

 

[Hyrde]

Well i don't really have the funds, time, tools or know-how to do that.

It's a little strange how the "new" used engine had no oil deposits on it's plugs and suddenly after i start using it it does.

I do think the piston rings may have become stuck after the used engine have been sitting a while, and it is the most likely option.

I will not be bothered to do that and if "nothing else" works i will simply not bother and continue to idle when going down hill.

 

[demarpaint]

Originally Posted By: Eddie
High intake manifold vacume will draw oil passed weak picton rings & worn valve seals. Nothing will help this except replace worn parts IMO. Ed


What the others have suggested is worth a shot, but from my experience I think Eddie is spot on.

 

[Hyrde]

That would draw it straight into the combustion chamber wouldn't it. My oil pools inside the intake manifold and it takes some WOT driving before i purge all the oil out of the manifold.

 

[Trav]

You could try some ProTec.As you live in Norway it should be fairly common,get two of the green can.

Remove the plugs and put 1/4 can down each hole overnight,put the plugs back in loosely and remove them the next day.
Turn the engine over a few times before installing the plugs again,start the engine.

Warm the engine and idle for about 45min with the second can in the oil,it should free the stuck rings if there are any.
Do a short OCI and repeat in the oil.

I doubt it has anything to do with the throttle body its a more likely to be drawing oil past the rings from what you describe.
The rings may be just plain worn out but its worth a try.

 

[Hyrde]

I've been looking for a miracle product and I will see if I can find ProTec if the Auto-RX thing I'm trying now doesn't work out (it takes a while to see results apparently). We have an Auto-RX importer in Norway. If neither work I will no longer spend money on miracle products.

 

[Bluestream]

Compression test or leak down test may give an indication of the condition of rings/valves. Don't rule out Eddy's suggestion of worn valve seals. I have seen many engines fixed of oil consumption issues with new valve seals. This is not a hard repair, or expensive if you get someone else to do it..

 

[FowVay]

But didn't you already change the engine once? Definitely do a compression check regardless.

Is it possible to have excessive crankcase pressure pushing the oil into the intake due to worn rings?

The throttle closed, oil pooling, and commonalitiy among two engines seems odd. I'm curious to see how this one turns out.

 

[Hyrde]

Compression is (pulley side) 190-180-180-180 (flywheel side) no change with a little oil in cylinders.

Old engine was 180 180 150 180 (dry)
180 180 180 180 with a little oil in cylinders

 

[antonmnster]

Sounds like worn valve guides to me. Vacuum is pulling oil right off the head and down the stems. I'm not familiar with that engine but generally they aren't too bad to change and not that expensive.

 

[Trav]

No miricle product just a solvent that will free a stuck ring if this is an issue its probably an oil control ring sticking if anything as the overall comresssion seems okay.

It could be worn guides or stem seals but these will usually cause smoking at startup and idle also.Do you get a good blast of blue smoke when you fist start the engine in the morning?

You can try plugging the PCV hose and drive it again,see if there is a difference.

 

[wiswind]

Intake vaccum will be at MAXIMUM under the conditions you mention.....

Intake vaccum will be at MINIMUM under Wide Open Throttle.

As mentioned by TRAV, you could remove and PLUG the PCV line at the valve cover and see if this changes the situation.
I do NOT recommend this as a fix, just as a VERY temporary test to see if it is being drawn in through the PCV line.
It is normal for some oil to come in through there, but you want to know if it is in the amount that is causing the blue smoke.

AutoRX is a good cleaner, but won't fix worn parts.
So you are spot on in not thinking the problem will be solved by a in-can product, beyond cleaning.

I could be wrong.....but the 150 cylinder going normal with some oil added into the cylinder would point to a ring issue for that motor.
I don't know what to think for the current motor........

 

[mechtech2]

Sounds like bad valve guides/seals.
Bad design if you have it in two exact engines!

Are you running your oil overfilled? Even by a mistake somewhere? Dipsticks can't be trusted. A real long drain and factory fill amount is best.

Never plug you valve cover anythings!
If you want a TEMPORARY PCV test, just pull the PCV valve out of it's socket and let it hang in the breeze.

 

[wiswind]

Sorry that I was not clear.
DON'T plug the valve cover hole where the PCV valve came out......
I intended for the PCV valve (or hose) to be plugged.......to prevent dirt from being drawn into the engine.
Leaving it hang 'should' work, but that is air entering the motor that has not been filtered and has not passed through the MAF, so the computer does not know about it either.

 

[Craig in Canada]

My first guesses would be the PCV system (cheap) or bad valve guide seals (not cheap). Maximum vacuum caused by closed throttle at "high" revs is pulling oil into the cylinders.

 

[Trav]

I meant plug the hose with a bolt or golf tee etc not the PCV opening.
Leave the valve in the cover sans hose,the engine will not build up internal pressure as long as the valve itself is in place.
Depending on where the valve is located just letting it hang may allow oil to splash out of the pvc opening on a hot exhaust manifold or something.

This is just temporary for 1 or 2 runs to see if there is a difference not a permanent fix.

 

[FL_Rob]

It feels like vacuum, but its actually called compression braking.The fault is usually the top and/or second compression ring,yes, the valve guides/seals could also be getting shot.As previously mentioned,check pcv.