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[JamesV6CDX]

Mmmm mineral oil, those were the days!

Will the mineral oil protect it well enough?

[Paul M]

That was exactly my first thought when I read the thread, the oil is way too thin for such a high mileage engine. I was just wondering how many replies there would be before someone mentioned it .

I wouldn't even use 0w40 in the Omega, and that shows no signs of burning any oil at all. Stick to 10w40 as recommended, or possibly even try 15w50 if that's within the specs (not sure if the hydraulic tappets will like it). I'm currently using Halfords ( ) fully synth 5w40, but only because I didn't have any VX stuff left when I decided to do the oil change, and the Halfords fully synth was on 2 for 1 offer so worked out cheaper than any of the semi-synth stuff.

[PaulW]

Definately needs some thicker oil.

Can't fault the vaux semi-synth 10w40 at all - used it all the time in the corsa.

[Martin_1962]

Oil control ring wear and too thin oil.

I would suggest 15/40 possibly even 20/50

On an old car I found that free Vauxhall mineral would burn a lot quicker than Esso mineral. So when my free supply stopped I had to start oil changes again rather than run total loss.

[JamesV6CDX]

Won't 20/50 be too thick for the hydraulic lifters, and strain the oil pump?

[Martin_1962]

Won't 20/50 be too thick for the hydraulic lifters, and strain the oil pump?

Try progressively thicker oils start at 10/40 then go up.

I can't see it straining, but possibly could play up the lifters - you can only try

[Martin_1962]

15/40 should do - used to use it in the Sunbeam

[Kevin Wood]

Thick oils can cause the lifters to pump up on some engines. Unless the topping up is a real pain I wouldn't necessarily worry too much.

At the risk of prolonging this "oil thread", however, I'm having some difficulty understanding why 0w40 is any worse than 10w40, 20w40, etc. Experience (including my own) says it is, but my understanding of the grading of oils is that the "40" indicates the viscosity is in a certain range at operating temperature (spec'ed at 100 deg. c IIRC). So a 0w40 should have a similar viscosity as a 20w40 at 100 degrees C and should be no more liable to slip through the seals and burn.

The "w" figure ("0", "10", "20"), as I understand it, indicates what viscosity it is equivalent to at lower temperatures, relative to a monograde oil.

In other words, the only difference between a 0w40 and a 20w40 is that, when cold, it pumps easier because it is equivalent to a thinner monograde oil. Oils with a lower winter rating are also usually more resistant to further thinning at higher temperatures (above 100 deg c).

James' engine probably spends most of its' time around 100 degrees C, making the winter rating insignificant, so can anyone explain what I'm missing?

Kevin

[Martin_1962]

It takes quite a long time to get the engine up to temperature - I would guess easily 5 or 6 miles minimum.

[Kevin Wood]

It takes quite a long time to get the engine up to temperature - I would guess easily 5 or 6 miles minimum.

.. and longer than that to get the oil fully up to temperature, of course. Maybe it's during the warmup phase that most of the oil is lost  :-/

Theory and practice just don't seem to meet for me, and it bugs me when that happens.  

Kevin

[Taxi_Driver]

Personally i would bung vx semi back in it......it always had that in it when i owned it.

I remember telling you James and also mentioned it in a thread that it used 1ltr/2k miles.

Then see what the consumption is like......as a comparision.

Since you have rebuilt the head on it.....i would expect it to be better than 1ltr/2k.

Much worse than that.....then theres summat wrong.....it carnt suddenly start using more oil.

[hotel21]

My tuppence....  

Its an engine with a telephone number mileage as well as goodness knows how many hours ticking over on 'standby' of a cold night with the heater on.  Its bound to use oil.   Check the Vectra handbook and see what the VX estimated oil consumption is, then double it or so......

Bigger potential prob is why the cylinder comp differences are larger than the recommended 10%.  No1 comp down or 3 & 4 increased due to oil presence from plug removal?

I accept what Mark says about pocketed pistons and that the oil will hide there rather than down the bores, but how about this...

Ensure plug holes are clean of old oil.  Remove all plugs, retake comps across all four - thats result 'A'.  Take compressions with throttle wide open (if cable) or inlet butterfly's removed if FBW.

Put a healthy measure of oil down all 4 bores and, with plugs removed and a suitable absorbent cloth strategically placed and held by your version of Debbie McGee, turn the engine over by hand/spanner then later jag it over on the starter (to avoid possible hydraulic lock) then take readings.   This is result 'B'.

Now read and compare comps.  If all 4 'A' readings are within 10% of each other, grand....  If one (or two) wildly out, potential problem with indicated cylider(s).

If the wet test comps ('B') are also within 10% but higher, then its simply a tired engine thats had a head job.  Oil does a temp job of increasing ring/bore seal long enough to get a set of comps.  If no appreciable drop in power output, use 15/50 or 20/50 to reduce costs in 'total loss' oil system.

If you still get 3 & 4 with increased comps in comparison to 1 & 2, then its looking like the head is at fault, despite overhaul.  If no difference in 'A' and 'B' then its the head, not the rings.

I know above wet/dry comp tests are like sucking eggs to you James but, to me, its worth a redo to ensure all is OK and its simply tired and has a wee thirst for oil.....    

[familyman]

The reason your not seeing any burnt oil smoke out of the exhaust is due to the catalyst collecting it for you. As the oil vapour is different for normal exhaust gases it doesn't pass through the cat as well when its cold, as the cat warms up it slowley starts to burn off the residue oil by which time your engine/piston rings have warmed up and sealed better so any more oil vapour is able to be burnt of by the cat.

[smoothomega]

Sounds a bit like a thread i started some time ago before i knew better   That was which 0#! is best  
Lesson learnt