Just changed the oil to some nice Vx longlife 5W30 synthetic.

I think my car sounds rougher now, especially when hot. Sounds a bit tappety when idling from inside the car and there's a slight rattle from the sump area when kneeling down beside the engine.

Could it just be that the oil is too thin for a 100,000 mile engine? Especially in this warmer weather.

I'm reluctant to drop out 5.5 litres of nice synthetic oil and replace with 10W40 just as an experiment.

Could I be suffering from the phantom big end knock? If so is it something I can ignore?

If it started to sound rough immediately after you did the oil change then it stands to reason that it is something to do with that. But I doubt the oil you used would be solely responsible.

30 oil is within Vx spec as they say the viscosity should be ’30 or greater’.

Having said that, most people here use 40 oil (10W-40 or 5W-40), so there is very little experience here with regards to use of 30 oil in the Omega.

It does however stand to reason that the thinner oil is not so good for a high-mileage engine, and as STMO123 said if the engine roughness started after the oil change then it is probably not a coincidence.

I have no ideas other than to drop that expensive Vx oil as you said… did you get it on Trade Club at least?

I'm not sure the roughness exactly coincided. It's worse when the engine's hot (after a long run) and the weather's been hotter lately.

The oil was from TC at least.

I'll certainly try 10/40 semi next time and perhaps bring the change forward.

I think I'll also try to locate the source of the noise better.

If you use a really thin oil in say a old aircooled volkswagen engine even though it's just been assembled with all new parts, then you will for certain hear more engine noise (tappets ect.) due to the larger tolerances used in a oldschool engine. It's the same with a worn modern engine, the tolerances are larger due to the mileage, and therefore you'll suddenly hear some rattles'n'tiktaks you perhaps hadn't noticed before with the thicker oil. 10W/40 should be what you need.

Against all advice, I'd been using Vx  5W30 synthetic in my 96 P Reg Omega for about 6 months before I wrote it off.
There were no unusual noises.
I think the engine was more responsive, and I'm sure that fuel consumption improved.
I’ll never know what the long-term effect would have been.

It really depends on the age and condition of your engine. The thinner oil will probably make your engine feel more responsive as there is less resistance for it to overcome. However, thicker oil will offer more protection, especially at high running temperatures.

Its a case of finding the best all-rounder.

wrote on 01. Aug 2006 at 16:52:

Against all advice, I'd been using Vx  5W30 synthetic in my 96 P Reg Omega for about 6 months before I wrote it off...

Sorry for stating the obvious, but this sentence sounds rather ominous I should think… :)

Markjay wrote on 01. Aug 2006 at 17:08:

wrote on 01. Aug 2006 at 16:52: Against all advice, I'd been using Vx  5W30 synthetic in my 96 P Reg Omega for about 6 months before I wrote it off... Sorry for stating the obvious, but this sentence sounds rather ominous I should think… :)

I don’t think the oil caused my accident. But it might have done! The car did seem faster! [smiley=thumbsup.gif]

JasonH wrote on 31. Jul 2006 at 21:44:

I'm reluctant to drop out 5.5 litres of nice synthetic oil and replace with 10W40 just as an experiment.

If you were careful, couldnt you manage to catch most of it....and if you change the oil filter as well....coz some will be in there as well and save it.

New Oil filter and 10/40.....if it doesnt make any difference.....then perhaps you will only need about 1ltr of synthetic when you change it again.....if it does make a difference then you will have to decide what to do with the synthetic oil.

Just a thought

Cheers

Taxi Driver wrote on 01. Aug 2006 at 18:43:

JasonH wrote on 31. Jul 2006 at 21:44: I'm reluctant to drop out 5.5 litres of nice synthetic oil and replace with 10W40 just as an experiment. If you were careful, couldnt you manage to catch most of it....and if you change the oil filter as well....coz some will be in there as well and save it. New Oil filter and 10/40.....if it doesnt make any difference.....then perhaps you will only need about 1ltr of synthetic when you change it again.....if it does make a difference then you will have to decide what to do with the synthetic oil. Just a thought Cheers

You could put it on ebay... ;D

Taxi Driver wrote on 01. Aug 2006 at 18:43:

JasonH wrote on 31. Jul 2006 at 21:44: I'm reluctant to drop out 5.5 litres of nice synthetic oil and replace with 10W40 just as an experiment. If you were careful, couldnt you manage to catch most of it....and if you change the oil filter as well....coz some will be in there as well and save it. New Oil filter and 10/40.....if it doesnt make any difference.....then perhaps you will only need about 1ltr of synthetic when you change it again.....if it does make a difference then you will have to decide what to do with the synthetic oil. Or I could send my missus round to top up the oil for you( see my oil overfill HELP thread) :o ;D Just a thought Cheers

I was thinking of asking the local garage how much oil to put in.... I reckon I could get another 8 litres in there before it came out the top.......