Diesel Servicing

In message , SH writes

The Montego TD of 15 years ago had an oil change interval of 12k miles.

Synthetic oil was used 7 years ago and before.

Oil drain periods have increased partly due to higher quality engine oil but there are other factors. Older diesel engines were indirect injection and these tended to contaminate their oil quicker than the indirect injection which is predominant today.

True the Montego TD was a Perkins direct injection engine, known to be capable of 300k miles of service & that was with pre-synthetic oils & normal oil filters. It begs the question why one manufacturer allowed such extended service levels & others set such low service intervals?

In message , SH writes

Because the Perkins was the first DI engine fitted to a modern car and everyone else was using indirect injection which necessitated more frequent oil changes.

And to answer your next question, "why didn't everyone use DI engines"? Well there were technical problems with producing a small DI engine (HGV's had used them for some time). The Perkins was the first of its kind to be successful.

Paul Well aware of the fact that Perkins was the first successful small engine DI, but I understand DI engines run at a higher compression rate (forcing more contaminants past the rings?) so why is it that the IDI's produce more contaminants in the oil or is that due to a less clean burn in the IDI's.

Anyway, my real question is would the new improved synthetics allow for longer oil change periods?

Steve

In message , SH writes

You have got that the wrong way round. IDI's have a higher compression ratio than DI's. That's why IDI's contaminate their oil quicker.

Personally I think that synthetics are good for protection on high performance cars i.e. cars driven under race conditions, but I don't think they offer any major advantages over a good mineral oil in terms of longevity or durability. In fact one of the more knowledgeable former posters here who worked for Alfa Romeo claimed that Alfa had evidence that synthetic oils had a tendency to "burn off" their additive package quicker than mineral oils.

I have just bought a Citroen C5 and it's oil change is every 12,000 miles in contrast to my previous Xantia which was 6000mls. I checked out the Oil filters and although the same in dimensions the C5's is double the price, I suspect that the material used inside must be more efficient in retaining particles and perhaps the design is such that there is more of a surface area to capture the offending particles or surely it would choke?

I was under the impression that it's the fact that the DI produce a cleaner burn, i.e. no pre-swirl chamber, that the oil gets an easier time. CR are similar iirc.

I don't think that's quite it, (though I'm happy to be corrected). The theory goes that the additive pack tends to deteriorate/burn off at the same rate in mineral or synthetic oil. As the synthetic oils often exhibit better oil control there is less need to top up and so the additive pack is not replenished as often.

Well, it made sense at the time! ;-)

JH

In message , JH writes

That's not what it says in my old copy of "Automobile Engines" by Arthur Judge. It says "The pre combustion chamber engine as mentioned has been supplanted by the turbulent head and direct injection types, for it has the disadvantages of requiring a high compression ratio".

Also if you look here:-

you will see three versions of the same 7.3 litre engine and the DI version has the lower CR.

Most modern cars I've come across don't require any top up between oil changes. Whatever the reasons, it seems that using synthetics doesn't necessarily give longer protection.

When PSA (Citroen/Peugeot) went from IDI to DI (XUD9 TD to DW10 HDI) they kept the compression ratio high. This means that the HDI is more fuel efficient than the Turbo D.

You don't have to reduce compression ratio when moving from IDI to DI, if you do, it will tend to make an engine quieter but less fuel efficient.

-- James

But what about in the average car engine? :-)

I'm convinced that much of the reason for extended service intervals is how attractive it is to the vital fleet markets rather than because the designs can take it. Fleet vehicles are often swopped at 70-80k coincidentally when many of the bigger scheduled services start these days...

JH

In message , JH writes

Its a similar story. The example I gave was good because it showed the same engine with both IDI and DI systems.

In car engines the IDI's are typically around 23:1 while DI are around

19:1

produce more

compression

Not necessarily. Mineral oils used in direct injection engines are classed partly on their ability to last while handling a high contaminant load but still protecting the engine. API CH4 is the latest heavy duty rating and is closely related to ACEA E3 which is to all intents and purposes the same as MB228.3. Oils meeting these standards are second tier SHPD [super high performance diesel] oils generally known to be suitable for use up to 45000kms. The first tier E2 oils are known for 30000km suitability in direct injection engines and these would have been recomended for the Perkins/Rover engine. Many synthetic oils only meet E2 although more and more synthetic and mineral oils are rated for multifleet [petrol and diesel] use up to E3 SL standards.

The oils recommended for long drain use in diesel cars beyond 12000 miles need not be synthetic. For instance MB only need a multifleet to mb229.1 in both engine types up to 15000 miles, although my preference would be to use a synthetic oil to 229.3 spec even though the oil and driving style are dynamically monitored and the service interval altered accordingly.

Long drain intervals above 12000 miles are either dynamically monitored as above or they have an overiding caveat stating that it should be serviced at yearly intervals at the longest thereby ensuring that only very high annual milage cars ever hit the distance limit.

evidence

package

If that is the case then we can assume Alfa use high quality mineral oils [unlikely because they would contain even higher chemical load] or they have short change intervals and/or short engine life. Quite frankly the Alfa man's 'evidence' should be easily available unless it is so much boloney, which it surely is.

Huw

small engine

compression

They certainly dumped less soot into the oil than indirect engines. Soot loads have recently increased due to later injection timing and increased EGR to meet emission regs.

CR are

Not so. Typical Di CR is 16.5:1 where an IDI may be around 21:1.

evidence

The additive package does not deteriorate or burn off. Some of Its properties are used up in much the same way that washing up liquid loses its effectiveness as more dishes are cleaned. The detergent is still there, it has not gone away but it loses effectiveness as it becomes saturated with contaminants.

As the synthetic oils often exhibit better

Synthetic oil control at the ring/cylinder interface is no better than good mineral oils and an engine that consumes one will consume the other. There may be a difference between some brands even though they share the same paper specification and the only way to know which a particular engine prefers is by experience. The differences are generally minor though I have seen significant differences at longer drain intervals between E3 and E4 oils.

It is interesting perhaps to realise that ACEA E5 oil is inferior in almost every performance aspect to E4 and only equal in most respects to E3.

Huw

compression

quicker.

time. CR are

efficient.

Nonsense. Almost all the medium sector engines that have a specific fuel consumption of around 200g/kW/h have nearer 16:1 CR than the 21:1 typical of the same class of IDI engines.

Huw

time. CR are

corrected). The

doesn't

coincidentally when

So how many regularly serviced to the book engines do you see failed before 200,000 miles or five years or otherwise before the rest of the car is junk?

Huw

retaining

The cynical might assume that they wish to retain their margins despite seeing your car half as often. Not me.

Huw