Oil Change Interval / Quality Of Oil

Interesting. I have been an LPG user for some years (1993 I bought my first LPG car, an Ex British Gas 4.2 Litre XJ6 sereis 2). 6 years ago my car at the time was a 180K 2.7 litre Rover Sterling running on LPG and I took part in a survey run by BP, Which involved me taking samples of oil at 6K intervals and sending them to be tested. As some of you may know there is little differacne in appearnce in oil used in an LPG burner comapared to new oil. Well in my case the car coverd 36,762 miles in the test period, without an oil change. The only change in the oil was a slight rise in acidity (and very slight) the Oil filter was taken off at the end of this and also inspected, and found to have no contamination at all. I tend to change my oil at 6K anyway!

Stewart

No, I didn't know and I think that's one of the best reasons for LPG use that I've ever heard.

It also says somthing that a 180K Honda 24v V6 would run another 36K with no need for a top up. I will admit to finding the 4 pot 2 litre in My XM a bit rough in comaprison, and have started to wonder about the size of the Honda engine/gearbox assembly vs the Douvrin V6 and gearbox...... Ok the Honda is a little smaller at 2.7 litres, but it will go on and on and on and on......... and the starter motor is real easy to get at!. But we can all dream!

Stewart

This post has been edited by Zaphod on February 11, 2007 02:18 pm

As somebody has already mentioned, fleet companies often pick their vehicles based on pence per mile costs, by stretching service intervals, costs to a fleet company, or company car user, over a 3 year period will be reduced. The manufacturers do not care how long their cars last once the warranty period has expired.

Oil - even the best oil - loses viscosity after just 3 or 4 thousand miles, the long-chain molecules which "thicken" the oil get chopped up. A “new” problem that arises by stretching service intervals is chemical stability; Oil goes acidic causing internal corrosion, particles that have made it past the oil filter need to be suspended in the oil, rather than allowing them to sink and form sludge. Oil must also be thin enough to decrease fuel consumption as well as allow the use of inferior quality batteries/starter motors, thinner oils need anti-foaming agents. Oil filters have got “worse” intentionally, they are there to manage the particle sizes allowed to float around in the oil, rather than filter them all out, this is because having too good a filter and stretching the service interval will just mean a blocked filter.

Add all these, often conflicting, requirements together, and the oil becomes 80% oil 20% chemical wizardry. The latter part of the oil make-up offers no lubricative properties - they are a means to an end.

In other words, we are being conned. The potential life of the used engine is being compromised to make motoring cheaper for the new car buyer. As Peter suggests above, you are better off buying cheap oil then changing it (plus filter) regularly – doing so will double or treble the longevity of your engine; Buy decent branded oil filters, generally, Volvo ones are of a very high quality, if anyone can source a Volvo-branded filter that fits their car – they’re on to a winner! Yes I know Volvo is part of the Ford Empire – they do have different spec filters – trust me on that!

That said – if you are going to abuse service intervals you MUST use decent modern oil, the simpler cheaper oil will not cope with the chemical stresses asked of it over an extended service interval.

Steve.

I believe that the longer service interval is dependent on using semi, or better still, fully synthetic oil of lower cold viscosity than previous. This lower viscosity reduces cold start wear and the synthetic oils are much more resistant to degradation. Gas turbine manufacturers cottoned on to this 45 years ago.

An oddity that I discovered is that the ES9J4 V6 fitted to my XM has oil change intervals of 12,500 miles, the same engine (you know what I mean) in my previous 406 had oil change intervals at 20,000 miles. What's that all about? Looks like another example of adjusting for the fleet market.

Before my last oil change, at 62,400 miles, the oil was pale straw in colour, little changed from new. Now at 69,900 mile the new oil looks much darker.

My gut feeling is that the new service intervals are fine provided there is minimal local work, in other words that the oil gets hot enough to boil off the contaminants. That's why my car only comes out of the garage for 30 mile plus trips, otherwise we use my wife's ZX which is serviced according to Peter's principles.

Derek

I'd just like to add my oil changing stratergy to the list........


I pop in a can of flush, drive 10 miles, cool off, drive 10 miles home, drain oil out and dispose of. (and get brownie points for taking wife shopping!)

I then fill with cheapest oil I can find, any old universal crap thats cheap.

I use it one day then drain it, pour it in the fuiel tank, and refil.

repeat 3 more times.


End of week change oil+diesel filter and fill your nice clean engine with quality oil.

dont put the original drained oil in as the flush fluid can be acidic to the fuel pump, and thats costly.

It costs no more to do that than a standard change of oil, as all the extra oil you bought has reduced your diesel bill.............

Remember to have a fair amount of diesel in the tank, as pure oil is hard to suck through the filters.