Need Oil Control Ideas

[rs899]

The engine on my Caddy has about 200k miles on its last rebuild.  With a good starter, it starts instantly.  Compression is 400 psi across all cylinders .

But all is not well.  It burns copious amounts of oil, even with a splash shield over the cam and a Mercedes oil separator installed.  Maybe a quart every 500 miles

It’s an 11mm block and I don’t think it would be easy to find the largest size O/S pistons  ( and I have a couple of better blocks anyway)

Would a re-ring help?  With 11mm block I may be tempting fate- should I just run it until it …runs away?

[8v-of-fury]

Well if it is burning that much and the compression is that high... I'd be doubting one of your readings.

Mainly the compression, because you know how much oil you have to put in.

I don't know if a serious oil burner will make near perfect compression.. Also did you do this comp test hot or cold?

[libbydiesel]

I have an AAZ that has excellent compression and yet uses about as much oil as diesel.  Seriously.  Like a quart per 50 miles.

To the OP, run it to a catch can.  I made one out of ABS with a plumb-quick fitting on the top drilled to accept a crank vent filter from my FLAPS.  Then it gets poured back in...  Plan on a rebuild soon.

[8v-of-fury]

Oh, interesting. These engines cease to amaze. What do you think the cause of the extreme blow-by is then?

[theman53]

If the compression is that good, check the cylinder head. I bet it is in need of seals at the least, if not completely gone through. With 400psi, I wouldn't re ring as you shouldn't gain much, if maybe replace the oil scraping rings to the 3 piece???

[libbydiesel]

I suspect that the oil control rings on my AAZ are either stuck or broken.  Certainly valve stem seals could be part of it.  A full rebuild is in it's very near future and so the specific cause is just academic.

[CRSMP5]

my queston.... you fill when 1 qt low or 1/2 qt low?? 1st 1/2 burns way faster then 2nd 1/2 why i ask...

queston 2.. turbo? i only ask that as if the oil return line is too low on the pan it will suck oil down... has to be above the oil level in the pan...

queston 3... what vac pump.. old diafram style with vent off front of block... will boost oil usage... remove block vent.. use pvc style breather filter on the pump.. and plumb catch can into block vent hole.. you would be suprised at how much this trick helps...

[libbydiesel]

CRAMP5, I'm not sure who you're asking, but that AAZ of mine is in a vanagon and the oil does enter the pan below the oil level just like all 200,000+ stock VW vanagon turbo-diesels sold in other markets.  I have also owned and worked on many that had a similar oil drain below the oil level in the pan without any oil consumption issues.

[CRSMP5]

i have always wondered that on a vanagon set up... but i think its more oil level when running...

how  this topic came up to me back inn 96.. .pree interwebz... when i installed my used bae turbo kit i put the drain too low... sucked it down all of a sudden when i never had issues prior.. someone told me my return was too low.. moved it up issue resolved..

and my questons were for the op... a few other ideas vs rings/seals/guids

[rs899]

To the OP, run it to a catch can.

I am basically doing that already.  The MB 240D oil separator runs back to the port on the block that was formerly used by the original vacuum pump.  I have the later piston type vacuum pump on it now.

my queston.... you fill when 1 qt low or 1/2 qt low?? 1st 1/2 burns way faster then 2nd 1/2 why i ask...

I usually refill when it gets close to the bottom line on the stick, and then only go as high as the halfway mark.

queston 2.. turbo? i only ask that as if the oil return line is too low on the pan it will suck oil down... has to be above the oil level in the pan..

.

No turbo, 1.6 IDI NA

queston 3... what vac pump.. old diafram style with vent off front of block... will boost oil usage... remove block vent.. use pvc style breather filter on the pump.. and plumb catch can into block vent hole.. you would be suprised at how much this trick helps...

New style piston vacuum pump.

I am pretty sure my compression gauge is accurate as it literally lights off in less than a revolution when cold.

I know it could use valve guide seals, but I question whether that contributes all that much to the consumption.

Of course, it needs a rebuild, but I wouldn't rebuild this block anyway as it already has oversize pistions.  I would likely take them out and move them to an original bore block, but then there's hundreds of dollars of machinist/parts cost and a lot of time.

If I felt there was a chance that I could re-ring it, and maybe rebuild a head ( which I can do for basically nothing, including new guides and seals) I might do that.  Otherwise, just keep running it.  It's really just going to be a third stringer to my Jetta and Cabriolet ( once that is re-engined).  I am really curious what could be doing this with such good compression.  Could a couple of oil rings be broken ?

I just hate to spend $3/week on oil when I have to drive this...

[8v-of-fury]

If you have a catch can that is actively catching all the oil out of the blow-by and you are still using that much oil, then there may be nothing left to do but rebuild. Probably just the head though as it would seem.

[rs899]

Is there any way on a diesel to tell, without pulling it completely apart, if it's the rings or the valves?

I wouldn't mind too much at all reworking the head, but reringing in situ I would rather avoid (BTDT).

I didn't think it would be possible that valves could contribute that much to consumption.

[8v-of-fury]

Well it is a 4 stroke engine, the fuel type doesn't matter so I would do a leak down test. You will hear where the air is escaping.

[rs899]

I don't think that's going to tell me anything, unless my compression tester is completely wrong ( but my ear tells me it's not since the engine starts so well).

The valves and rings are sealing well enough to produce good compression.  When the valves are closed it seals OK and it's not burning through the valves then.  If it's valves , it's burning  when the valve is open.

[damac]

My jetta engine had numbers just like that and close to same oil burning, although I did have some drips from the valve cover that I could not stop.  I also made a pvc type catch can inline with the stock setup and ran a low drain port down to where the block cover was.  I was getting bad blowby on that engine and it was trying to push oil out where it could, although never out the dipstick.

I broke the engine down and the bore readings said it needed to be bored out with some slight eggshape going on.

This car was involved in one overheating incident when a coolant hose broke and a family member drove it until it locked up.  I patched it on the road and slowly drove it home 20 miles but had to pull over every minute to refill with water, the head gasket had went and it would try and overheat.  Surprisingly that head seems ok to the eye and basic measurements with a feeler but I haven't had it checked out yet.

I also didn't have issues starting the car down into the teens on the first glowplug cycle.