Burning OIl

2004 Sirion SL K3-VE2.

Long-running issue with oil getting burned - about 1L per 1000 miles.

The oil gets burned slowly if I run the car gently, but increases as the car is pushed. If I accelerate gently, even pushing the revs up to 6000, there isn’t a huge amount of smoke, but if I floor it, there is a definite haze of blue/grey smoke left behind me. It’s worse if I have been following someone and I have been holding the revs up to 3000- 4000 for a few seconds to make sure the power is there when I need it. Generally, on acceleration, it sometimes feels like the plugs are getting clogged during that period from idle to 1500 - there’s a bit of hesitation.

So, what have I tried so far…

I tried a different PCV valve - no difference.

I tried putting a little restriction on the hose going from the throttle body to the valve cover - the one that isn’t under vacuum and is in front of the throttle plate. I left the hose with the PCV valve in it alone. The idea was to slow the amount of air running through the crankcase, because it looked like a load of oil was getting sucked into the engine through the PCV valve. I thought reducing that air would help because the PCV would be sucking less of a volume of air and would therefore not be grabbing a load of oil droplets as the air was rushing out of the valve cover. It made a measurable difference to oil consumption and definitely slowed the amount of oil getting burned. But the problem is that there was now a noticeable vacuum in the crankcase. The car still smokes if floor it.

So I tried something else. PCV delete. Under FOT, any blow-by leaves the crankcase via both the PVC valve and the non-vacuum hose from before the throttle plate. I noticed that this tube is always dry, where the PCV end is always very wet from the oil getting sucked up. So, as a trial, I got a cheap PCV vale and gutted it, then routed the gutted PCV valve to the non-vacuum end of the throttle body to make it a simple vent, then I blocked the vacuum hose that used to go the PCV with a bolt, and added a one of those little air filters onto the hose that used to go to the throttle body before the throttle plate. Again, there’s an improvement - the car doesn’t hesitate from idle at all, and generally feels more responsive. But I can smell oil fumes - so that’s not great for the environment. It still smokes if I floor it. But it does prove, I think, that oil getting sucked into the engine is an issue.

I’m onto attempt number four. I think some of the problem is the PCV sucking oil droplets from the valve cover. So I’m thinking of reversing the flow of the emission system. I want to put the vacuum tube with an inline PCV onto the other end of the valve cover (where it used to let the air into the crankcase) and have the non-vacuum end where the PCV used to be. I’m thinking this would put the PCV somewhere where big drops of oil can’t get sucked up, and it should close the system as it should be closed. Has anyone else done this? Can you see any possible drawbacks? I’m assuming that the lower air inlet into the valve cover just goes straight into the valve cover but lower down.

I’m going to assume the car will always smoke if I floor it. Now I am just looking at ways to reduce the amount of oil it uses when used more gently.

Honestly I didnt read everything you tried as it will be the rings. They get gummed up when vehicle hasnt had a good service life and they get stuck in the piston. You can try the atf or upper cylinder cleaners to try to help to try to free the rings up but really they need to be replaced and it would be a good idea to make the holes in the pistons behind the rings slightly larger this will help them not clog in future.

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The rings were replaced and the oil holes in the pistons cleaned about 30 months ago, but not enlarged. Also, the head was refurbished and skimmed - valves and seals. I’ve been running it on synthetic 10W40 ever since. That made a huge difference, but it still drinks more oil than I would like.

I just don’t understand why the PCV is where it is - it’s almost bound to suck oil.

I did consider a catch can, but I’d be emptying it every other week!

sorry I did not realise that

My fault - I forgot to mention it.

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Attempt #4 has worked somewhat.

Changed the direction of air flow through the crankcase of the PCV system.

The vacuum from the throttle body after the throttle plate goes through the PCV valve as before, but the PCV valve is plumbed into the lower port on the crankcase cover using a short piece of vacuum tube. I’m using a new piece of vacuum tube and a PCV with the innards removed to make the connection from the throttle body before the throttle plate to the crankcase as the source of fresh air for the vacuum to draw on.

It took 500 miles before I noticed a lot less smoke on acceleration, and it seems to be using a lot less oil as well.

I have also put a reducer into the low vacuum hose to reduce the air flow a little.

I think the reason this works is that the PCV no longer sucks up big droplets of oil from the area above the valves because it now sucks from a less droplet-filled part of the valve cover.

If anyone is interested (and I get that most won’t be) I’ll add some images to explain what it looks like.


I’m interested! Can you show us what it looks like?


Unplugged the PCV from the rocker cover, leaving the PCV in place in the hose.

Then I twisted the hose with the PCV attached over to the other side of the valve cover towards where the other hose goes onto the valve cover. The PCV is on the left - you twist the hose to move the hose with the PCV to the right hand side.

The other hose goes into the throttle body at the front of the throttle body. I removed it at the throttle body and pushed the end that was on the throttle body onto the PCV to make the connection between the throttle body vacuum side, via the PCV, to the connection at the base of the valve cover. That’s the vacuum side done.

For the fresh air inlet, you need a new piece of vacuum tubing and a PCV with the innards removed to fit into the hole in the valve cover where the PCV used to sit and the other end goes to the non-vacuum end of the throttle body connection.

It’s much easier to do, than describe!

What do you know about the rebuild? You mention piston ring groove clean. New rings? How were the cylinders honed (if at all)? Valve stem seals replaced?

PCV should only work at idle (the vacuum in the inlet manifold closes the valve). It can be deleted completely. But you need crankcase ventilation, and that would be the thing that goes through a catch can.

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The local garage said they replaced the rings and spent too long cleaning the oil holes in the pistons - the way labour is here in the UK, new pistons would have been first choice for most cars, but Sirion pistons are expensive and copies might not be reliable. They had the head skimmed, new valves and seals new head bolts and did a hone. They checked the bearings for wear and left them, because they looked good. I trust the garage - but in reality how good a job they did, I don’t know.

I did try a PCV delete, but the smell put me off that as a long term idea.

I’m thinking that now I have found a way to reduce the oil use, a catch can might be worth a go. With the ventilation going the other way, I can put the catch can to the right of the engine where there is plenty of space without having to run excessively long vacuum lines.

The thing I don’t really understand is why the car was using so much oil despite the work being done to free the rings and sort the valve seals out. At the moment, it seems to be much better. But there’s no doubt the car is still using oil. My previous car, a little bubble shaped Micra 1.4 had 180,000 miles on the clock and didn’t use any between oil changes.

To really understand “why” it would be worth getting an oil analysis. I’ve not done this for a long time, but in the past I’ve done so and it revealed problems that I could only have guessed at.

When running the engine in after the rebuild: did you use a run in oil (low detergent and high zinc)?; and, was the engine run at lower revs but under high load (high combustion pressure is needed as the pressure that gets in behind the rings seals them more so than the spring tension and they need to take the shape of the cyl)? The blocks are very soft and when honing only a few strokes are needed. Doing this by hand is hit and miss, but mostly works. The only way to get a correct home is by fixed machine. A manufacturer oil recommendation is not to do with bearing clearances but with the hone pattern (this is what oil and piston/ring manufacturers say).

If pistong/ring/bore clearances/finish are the issue it’s a double edge sword. It will burn and loose more oil and the combustion will get past the rings to pressurize the crankcase blowing oil out via the pcv, breather and sometimes through gaskets.


Interesting read

If you open the oil filler cap when idling you will soon see that theres no chance of air being drawn into the engine via the pre throttle port…theres slight pressure in the engine always it seems and this woild resist any “intake” to the head

Maybe that was the plan with it by the OEM? but i find it hard to see how it would work…as surely even the non pcv port would have a slight pull on it from the IACV doing it ms job holding idle? Theres a slight suck at the airbox inlet so would assume the same at the the now closed throttle plate?

Im planning on removing the post throttle connection completely on mine, but still run both head breathers…and after a bit of thought am going to try the following

  • mount my old subaru hyperflow 4 port catch can up on back firewall (got heaps of can from previous cars lol)

  • plumb airbox side (non PCV) head breather with ½ inch hose to catch can

  • remove green PCV valve and install a ½ inch male to male hose joiner into grommet (fits perfectly)
    Install a ¼ barb to ¼ thread hose connector into the male to male barb as a restriction, obviously on the can side so it cant dislodge into the engine! (Physically screws into barb, may use some sealant but it also wedges into the hose ok) As this PCV line only runs a tiny port…and if you remove it when running theres a lot of oil getting flung around this area that i fear may assist it getting drawn into the line. May even restrict it a touch more or create some baffle later as the ¼ inch is still more than the PCV hole

  • run now restricted ½ inch hose to catch can …so thats the engine to can side done

  • join a 3rd ½ inch hose from catch can to pre throttle port (and cap the 4th port of the can)

  • cap old post throttle port with rubber bung

  • will try keep all lines high up in bay to assist with oil “running back” to the head where possible …this helped massively with my subaru track car and was proven time and again

  • and finally a easy to access drain line on catch can

May need to play with PCV side restriction more, and i also have a 9-9.5 mm hose as an alrernative to run (same size as PCV) to can that can provide some restriction…may even just drill/gut the pcv in that case…but also have a suitable ½ to ⅜ male to male joiner that fits (but i still think it needs some sort of oil baffling restriction on that side

Will draw a rough pic up to show what i mean as might not make sense :joy:

Yellow is can

Green line has restriction via barbs/hose/gutted pcv

Orange line is unrestricted as normal

Blue X is capped post throttle inlet

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