The Negotiator said:

Why would they recommend an amount of time which would damage the engine?

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The truth is that the engine is always wearing, it's just that there's a balancing act for the manufacturer between giving a short enough service interval that engines don't break prematurely, and a long enough service interval that people are happy.
Even if you change the oil every 100 miles, there will still be engine wear. Likewise even if you don't change the oil for 50k miles, the engine won't break as a direct result of the oil. The service interval is just an arbitrary distance given by the manufacturer. I remember a few years back when Vauxhall had 12k mile service intervals, they changed it overnight to 18k intervals. This wasn't suddenly because the engines became 50% more reliable or hard-wearing, it was because they wanted to sell more cars, and that's an easy way to make them more attractive, particularly to fleet managers.
H

It was also probably due to testing showing that it was fine for it to have such large intervals. It's not in a company's interest to give a service interval that is too long. Especially for fleet cars. Why? Well Ford for example sell thousands and thousands of fleet cars, if they said 18k but 12k was better and the engines all failed at 100k instead of 150k and certain fleets were high mileaged fleets, that fleet wouldn't go back to Ford again would they, regardless of intervals.

It is my opinion that for a reason interval you could go longer than 18k but that's a better safe than sorry figure for certain engines.

When I watched Discovery a while ago they had a program on car testing and they had computer simulations for that, which actually drove the car on a rolling road for a lot of miles in different temperatures, speeds, winds etc.

They actually had a machine to open and close the doors, push an artificial "butt" onto a seat to check wear (obviously not on the Ulysse judging by the number of seat bases they have changed).

I am not saying oil changes aren't good, but for the money and the benfit you get, I can't see it is worth changing it more often on a modern car if you use quality oils. And apart from that, I am lazy and would have to pay the garage to do it.

By the way we got the Punto Sporting last week for my sister in law, it is a great car. A July 2002 one with 40K miles, air con, bright yellow, new Pirelli tyres, full Fiat hostory, new brakes etc really good condition (no scratches at all) for £4,700.00 with a extended warranty after the Fiat one runs out in a couple of months. Not a bad price for a garage car I suppose.

RobW said:

BTW 5w/40 full syntetic on offer at halfords for £15

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is that real synthetic or a hydro cracked mineral oil labled synthetic?

the endurance testing is done to assure reliablity - and to be as representative of real life as possible, i used to be a relaibility engineer at a diesel engine manufacturer

we were under pressure to extend the change interval but the test engine failed the test, we used to send samples off for analysis to see how much contamination was in the oil - so a lot of thought does go into the recommended intervals

some really black stuff was still fine, particles not the prob, its the combustion by products acids etc that are held in suspension that break down the oil

basically - use the best oil u can afford and stick to the schedules

dave said:

are but the recomended would be for normal driving, not 140 mph on motorway (i wont menshion no names, but its a girl )

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I've seen "a girl" driving at 130 mph on the motorway in the middle of the day!
Doing 150 along a straight dual carriageway at 4am is one thing (Naming no names ) but in the middle of the day...
Anyway, returning to testing, real-life testing is a part of manufacturer's testing cycles, as well as extreme tests. I read an article on it a while back about Ford's testing procedures. These include the "RAC test", where an engine is started and just idled continuously, and the "Boy-racer test", where the engine is started from cold and taken to peak revs repeatedly.
All these tests are done to find out what it takes to wear and break an engine, but you can't set a figure on what is ok and what isn't, so the service interval given is in reality just an indication. It's just that if you haven't stuck to the advice, your warranty won't be honoured.
I believe Nissan test their engines by driving everywhere at 40 mph, complete with pipe and flat cap
H

dave said:

is that real synthetic or a hydro cracked mineral oil labled synthetic?

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label says

formulated to the same protection and performance standards as the leading brands

for maximum engine protection under extreme loadin or enthusiastic driving. also suitable for use in the latest turbo diesel engines

....blah blah meets Porschand BMW spec

smells like coconuts too - just like motul stuff i used to use

so, duno, yea probably!

The Negotiator said:

It is my opinion that for a reason interval you could go longer than 18k but that's a better safe than sorry figure for certain engines.

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There are so many factors involved that I wouldn't want to generalise. On turbo cars don't forget that the oil also feeds the turbo, which wears as fast as, if not faster than the engines. Some cars also use a fair amount of oil anyway, turbo'd coops can use up to a litre per 1000 miles (as stated in the handbook), so not only do you use 5 litres at every oil change, you can use 5 litres in between every oil change to. I reckon that in 18 months of running my coop, I've spent around £250-300 on oil.
Didn't the Mitsubishi Evo used to have a 4500 mile service interval?
H

I think one of the evos does, possilbly lower, and it was re; oil use.

I am not talking about performance cars as I simply don't know

The service intervals on modern cars seem far too long. My mum's Citroen C5 has a service interval of 20,000 miles, its got 6000 to go until the next one is due, but I checked the oil the other day, not only had it used a litre of oil, but the oil on the dipstick was filthy. Thank feck its under warranty...

The main reason for extended servicing intervals is down to better quality oils and better tolerances on the machined engine parts.

I am in the same business that RobW was in and get involved with engine teardowns after reliability testing. I can assure you that servicing intervals are not a best guess or extended just to sell a car, it's because this is what the engine will take without any premature wear.

Rob - where you in Peterborough, Birmingham, Daventry or Darlington?

Here's some food for thought regarding performing earlier oil changes than recommended. When the engine is started up after the oil and filter change, how long is it running with low or no oil pressure as the system fills up the filter etc? Are you actually doing more damage in reality?

RS Pilot said:

...it's because this is what the engine will take without any premature wear.

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What is premature? Define it.

RS Pilot said:

Here's some food for thought regarding performing earlier oil changes than recommended. When the engine is started up after the oil and filter change, how long is it running with low or no oil pressure as the system fills up the filter etc? Are you actually doing more damage in reality?

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Depends if you disconnect the coilpacks and turn over the engine till the pressure rises first. When the engine is stopped large amounts of the oil drain back in to the sump anyway. It's only the filter itself that needs re-priming after a change I'd think. So you are damaging your engine when you start it... just like when you run it.
H

I guess premature is probably around 10 years and about 120-150,000miles now, because after that the car isn't worth a lot now and that is how long a lot of people expect a car to last without much work. Probably why a lot of warranties won't go past 10 years or 100,000 miles.

After an oil change you need to prime the whole system because it all comes via the filter, but sythetic oil sticks to engine parts anyway so unless you flush it during an oil change there will be some left while pressure comes up.

I would guess winter starts are the biggest killer. That's why a large number of people in Skandinavia have engine pre-heaters.