Possible for vacuum leak to cause engine oil to be sucked into combustion chamber?

Ever since doing the timing belt project, valve-stem seals followed by removal/cleaning of intake manifold, I've been working through various issues that for the most part have now been solved. I've started a new thread to cut to the chase of the one most troublesome problem remaining: I'm burning crazy amounts of oil all of a sudden. My engine, which used to consume roughly a litre of oil per 700-1000 km is now consuming a couple of litres per 100 km!!! Pistons #1 and 3 are covered in oil before every start, and the last couple days #2 has been starting to show signs of oil. The engine is choking on this oil and I'm at a complete loss.

I've found numerous threads of sudden excessive oil consumption following the timing belt job and/or intake work - but none of them named a specific cause/solution to this problem, even though some threads went on for several pages of troubleshooting.

I did see a few references to a vaguely described theory that a small vacuum leak can siphon oil into the combustion chamber through either the valve stem seals (even if the seals were fine), the piston rings or both. Is there any validity to this theory and if so, how specifically would it occur, and how can I isolate the cause?

• I've crawled under the engine and examined every angle with a good light and mirror searching for external leaks. Only found one very minor, new since this work began, leak from one oil pan bolt - very small seepage. And on an unrelated note, my knock sensor is oozing goo.
• One weird thing I found after pulling the exhaust shroud) was the lower left exhaust manifold bolt (facing the engine from the front of the car) was hanging on by only one thread, and covered with oil. I've never done any work to the exhaust - dunno how that bolt didn't fall out unless the shroud was keeping it in. I'm sure my cat is now toast given all that oil coming out of the exhaust.
• I've just had the valve cover off for the third time, and checked every single valve stem seal (already replaced with new set from Mazda once in the original instance, and second time to rule out installation error after I noticed an increase in startup smoke). Front engine oil seal is new, camshaft seals new (put a light skim of high temp silicone around the outside edge of all three to rule out minuscule leaks).
• Wiggled the valve stems as best as I could (didn't have a dial gauge) and results inconclusive. No oil in coolant, no coolant in oil.
• Sprayed carb cleaner all around the engine when it was last running, didn't detect any leaks - although I wasn't able to aim the spray underneath the engine (ie underside of the intake manifold)

I do plan to pull the engine and do a complete overhaul eventually, however I can't afford to do it at the moment, nor can I afford to even drive the car at the moment with all the oil going through the engine.

Any help greatly appreciated - I need my daily driver back!
2003 Mazda Protege5, 2.0 FS engine, Manual Transaxle

Up until about the mid sixties, it was common for engines to just vent crankcase fumes to the outside world via a road draft tube. Then enviromentally conscious people and government agencies decided that was no longer acceptable, and engines began digesting their own fumes using intake manifold vacuum to suck the fumes out, usually from the valve cover and controlled by a thing called a PCV valve. Weak vacuum and/or increased blowby typical of worn engines and/or plugged pcv valve can allow pressure to build up inside the engine which will push oil past rings and valve seals regardless of how good they are. I've heard of backyard mechanics implementing a road draft tube to get more miles out of worn engines.

Are there symptoms of a vacuum leak (other than the oil burning theory)?

A vacuum leak causing oil burning like Rick described is possible, but I don't see it causing as much burning as you have. And a vacuum leak would cause low idle, so if it isn't idling low, I'd look elsewhere for the cause.

What were the conditions of the cylinder walls when you did the rings? Did you hone them? Did you offset the gaps in the piston rings?

x2 for PCV. Is it oil fouled?

If so - vent to atmosphere and plug the vacuum line.

You'll want to plug the small line that goes to the air cleaner tube as well, if you disable the PCV system.

Your knock sensor is oozing goo?? That is a blind hole there is no way oil should be coming out of it.

I'm willing to bet you screwed the knock sensor into the oil pressure sender hole. They're next to each other on the rear of the engine.

Bad valve stem seals (unless they were all bad) will not drink over a liter of oil in 100Km. It's coming from somewhere else. What city are you in?

Maxx Mazda said:

Your knock sensor is oozing goo?? ......

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Our knock sensors do that... There has been a few old threads about it.

They get old and gooey eventually...

Hi everyone,

Thank you for your thoughts. Things keep pointing back to the PCV system as an "obvious solution" but if that isn't it I'm stumped. I've been delayed with troubleshooting due to a particularly finicky episode getting the timing belt to line up properly this time around. Argghhhh! Just came in for a quick break and then I will put the belts on, clean up the last few items and then test the car again. I did find a bit of oil on the end of the PCV valve, but nothing excessive - unless the intake is sucking it all away.

While I had the valve cover off I pried off the two metal covers inside and re-siliconed them back together at the suggestion of a mechanic friend (Ford). Apparently that system of chambers is to separate the air from the oil as it goes through the system to prevent the oil from leaving.

I have tested the PCV system in so far as to shake the valve, pull the valve while running and feel for vacuum from the intake manifold side and at the end of the PCV valve, and my friend has given one additional test to try. Apparently there is a very small amount of vacuum running through the valve cover as part of the PCV system and the additional test is to pull the vacuum line from the intake hose (going to the valve cover) and put a business card over the end. If it holds, PCV system functioning. If not, something is wrong. Apparently the amount of vacuum here is too small to register on a vacuum gauge. I'll post the results once I conduct the test later today.

The PCV valve is only a few months old, and seems fine, however it came from NAPA and I will likely replace it with a new Mazda one this week just to be 100% sure.

@Maroon, idle has been fine. As I mentioned I have sprayed carb cleaner around the engine (the places I can reach) and so far have not found any detectable leaks. Aside from listening by ear, I'm running the Torque app on my tablet so it's easy to see exactly what the RPM is doing. I haven't rebuilt the engine (YET!) so I have no idea the condition of rings/pistons/cylinders. I just can't afford an overhaul right now although I'm game to do it down the road.

@Maxx Mazda... LOL... what PCB said.

Stay tuned for updates! If anyone has any further tests to try, and/or ideas as to cause - keep 'em coming!

Quick update - just before heading out I was checking something else in the service manual and I happened to pass by the PCV valve section. As a double check I just re-did the "blow" test and discovered that air is now passing through from the intake side - it didn't do that before and isn't supposed to. Sigh. As well, these new plugs are toast - AGAIN! so that's two things I'll need to pick up today before I run it.

On another angle, have you checked the oil return passages? If oil is building up in the head, not draining back to the crankcase fast enough, it will start going bad places.

I wasn't aware the knock sensors leaked that s*** out of them. Thought you were implying there was oil coming from around it.

Have you got any photos of the engine top end while the valve cover was off?

LostinCanada said:

... I just re-did the "blow" test and discovered that air is now passing through from the intake side - ...

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I just did the blow test on my new in the box pcv valve (Fram fv289... I stock up when I order from Rock auto...) and I CAN blow slowly through the small end of the valve... it takes a bit of wind to close it.

(the other way blows freely)

I'm pretty sure it is not defective as I remember the same thing on pcv valves from other cars.

@pcb I'm just quoting straight from the service manual - no air air flow. My new in bag pcv valve from Mazda does not pass air from "B" although there is a brief lag to close the valve - I gave it a good blow, not a slow blow... . Tested a whack of times before installing - it's very consistent. The old one simply passes air from both sides... NFG I guess.

@rick3478 as far as I can tell I don't seem to have that problem.

@Maxx Mazda - the goo is quite distinctive: blackish brown, sticky and shiny - somehow they pack a lot of that stuff in that little knock sensor and when it comes out it makes a big mess. Apparently it's very common and the sign of a slowly failing knock sensor. I'm not getting any codes so I assume it is still limping along. I checked the price from Mazda and that part is simply going to have to wait for now.

On initial start I was blowing smoke from both ends - engine and tail pipe, but I think the engine part was just oil from the exhaust manifold and seems to be mostly gone now. To reinstall the bolt I found dangling I had to loosen all the exhaust manifold bolts because the metal gasket was in the way - hope that doesn't mean a bend or tear. It's on my list of things to replace, provided I can get the car running right in the short term (otherwise I'm going to take it out back and shoot it!). I left the shroud off so I can keep an eye on it.

I've got new plugs which I will put in tomorrow, and do a compression check while I'm at it. A neighbour lent me a compression gauge - just hope it fits 14mm and works - it looks very old! And I'll check the oil after it sits overnight. I did half the test drive on the old pcv valve and half on the new, so it might be too early to judge. Plus the PCM just reset. More to come!

LostinCanada said:

...The old one simply passes air from both sides... NFG I guess.

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Yea that's NFG.... Your other issues may be pounding the hell out of your PVC valve. Perhaps your new OEM one is more durable...

LostinCanada said:

I'm not getting any codes so I assume it is still limping along. I checked the price from Mazda and that part is simply going to have to wait for now.

Click to expand...

My knock sensor has been gooey for years... I'm not gonna worry about it...

Ok - time to isolate the PCV system to see if my condition improves! I installed the new PCV valve and it is already compromised after a couple of drives. When I shake it it sounds full of oil and now fails the blow test. And I'm getting occasional random misfire codes - I'm guessing from the oil.

I just want to be sure I understand how to do this correctly...
I should:

1. Plug the air intake line that brings fresh air into the valve cover,
2. Remove the PCV valve and port a vent line towards the road,
3. Remove the t-fitting from the intake manifold and install a straight connection in its place.

Is this right? Hope somebody in the know can confirm this asap (Thanks for the suggestion rick3478!)- I'm going out to do the compression test and find some tubing/plugs in the next few hours. Then a road test to see what happens to the oil eating behaviour of this engine.

As well, does anyone have pictures from an FS rebuild? I understand the valve guides can be replaced - I'd like to visually understand how the oil passages are routed, and how the valve guides are installed. Another fellow in my original thread is also having leakage past new valve stem seals (not my only problem, but one of them) on cold engine, and I wonder if the valve guides can become loose or cracked in some way.

Thanks!

At this point, I'm willing to bet it's a bad head gasket. If combustion pressure is allowed into the crankcase, it will force oil into every nook and cranny that it can.

On a side note, what do you fly, and what city are you in? I've been YYC based for about 10 years now. Thinking about making the jump to big red, but I just love my current schedule too much! Feel free to PM me.

LostinCanada said:

Ok - time to isolate the PCV system to see if my condition improves! I installed the new PCV valve and it is already compromised after a couple of drives. When I shake it it sounds full of oil and now fails the blow test. And I'm getting occasional random misfire codes - I'm guessing from the oil.

I just want to be sure I understand how to do this correctly...
I should:

1. Plug the air intake line that brings fresh air into the valve cover,
2. Remove the PCV valve and port a vent line towards the road,
3. Remove the t-fitting from the intake manifold and install a straight connection in its place.

Is this right? Hope somebody in the know can confirm this asap (Thanks for the suggestion rick3478!)- I'm going out to do the compression test and find some tubing/plugs in the next few hours. Then a road test to see what happens to the oil eating behaviour of this engine.

As well, does anyone have pictures from an FS rebuild? I understand the valve guides can be replaced - I'd like to visually understand how the oil passages are routed, and how the valve guides are installed. Another fellow in my original thread is also having leakage past new valve stem seals (not my only problem, but one of them) on cold engine, and I wonder if the valve guides can become loose or cracked in some way.

Thanks!

Click to expand...

I read this while investigating the oil consumption issue that my car had. My mechanic buddies all said valve seals when I described the symptoms, but the condition was too severe to be a valve seal.

He installed a rebuilt head with the same issue. I don't know if there was ever a resolution, but it wasn't to be found in the cylinder head.

http://www.mazdas247.com/forum/show...he-Mornings-and-leaking-oil-from-exhaust-port

@MrGiggles - do you mean an oil consumption problem you had before you did the JDM swap? Thanks for the thread link - I'm reading through it now.

Thought this was priceless: "FYI, it's not uncommon for oil rings to collapse and create the symptoms you're describing. Generally they collapse from a lack of oil changes (carbon builds up in the ring lands and makes them stick). You'll still have great compression but it'll burn oil like a mother fucker. " Yup - that's me...

Made it to Lordco with a jury-rigged PCV system delete and am now rocking 2 proper plugs on the IM, one plug on the valve cover (intake air supply), one plug on the air intake line (to the valve cover) and one 2' hose from the PCV valve grommet. Hope that is correct. I'll conduct another test drive tomorrow to see if I retained any oil as a result of the delete.

It bugs me when I find threads with similar problems, but then the author(s) don't ever identify the cause/solution. When I get to the bottom of my issues I resolve to give a conclusion here!