Oil type/changes

[kmh001]

Well there you go, you of never thought that. Well done Mal I think I might get a direct bat line to you for when I get confused talking to people with all these wonderful ideas....

Not having a go at you at all, more directed at the oodles of guys who have been indoctrinated into the 5000km myth. Main thing is I hope it's helpful.

[240MPS]

I'm aware of that, I read all of it yesterday and bought it back to life because of the 5000k myth because if mazda say 10,000k's it should be ok and it's only because I listen to people I get it done every 5000k's. So thanks, I will be re evaluating my spending.. And I also mention different oil types and to stay clear of Mobil 1 in the MPS which I used in my HSV's....???????

[kmh001]

That's a much more difficult question. I've used Mobil 1 a lot over the years and I've used it in the MPS but I use Castrol now, only because it's cheaper than Mobil 1 and I don't consider it be inferior.

I've seen a Mazda recommendation to avoid 5w-30 in cars that have problems with smoking, but I've never seen any evidence to justify specifically avoiding Mobil 1.

Is it just your mechanics opinion, or is there something more to it?

[240MPS]

Just the guys that work on the MPS Race Car, I just can't remember the reason now.

[shakespeare]

Thanks Mal, another good explaination.

One question, my wife has a DI turbo VW Jetta and most of her driving is short runs (15-30 mins) we take it on a good country run (800kms) approx twice a year. I also take it for an occasional spirited run, with the explaination that the motor needs a good run to make it last (but seriously I enjoy giving it a good squirt )

VW recommend 15,000km or 12 month service intervals, given the short runs should I be changing the oil at the half way point?
Thanks
Chris

[MattMPS3]

Really interesting info there Mal,
I think one of the key reasons there is such a vast difference between change intervals on the US & European markets is the oil that is specified in each respective country, I recall reading that the Mazdaspeeds in the US were specced to run on something like a 5w20 (due to emission or economy regulations?), where as we have a much broader spectrum to choose from, 10w40 being the more popular choice, this is possibly also why so many cars are blowing up over there, the oil is probably about as protective as dish soap towards the end of its cycle, throw 300whp on top of that and stuffs gonna break.

Out of curiosity, what are your thoughts on full (totally lab made) synthetic, vs a synthetic derived from a mineral base (i.e Royal Purple), I have heard some very mixed reviews on both and their respective applications in both turbo & NA applications.
Some believe the mineral based oils are better run in turbo engines as the additional heat and stresses break down the synthetic oils quicker, conversely the synthetics are better suited to race prepped high revving NA motors as they offer better protection in these scenarios, and I have also heard the complete opposite to these examples.

I am sceptical about the full 10k service life though, attached is a UOA on my Royal Purple after 8500 k's, its showing signs of breaking down and it is advised that this is a good change interval.
Can I get your thoughts on this particular test result, I know fuel dilition is up, we all know that is the bane of a DI engine.

[kmh001]

Frequent short runs could increase the quantity of soluble contamination in the oil. I've known people who found the oil level on their dipstick increased over time because they only used their car for short trips.

If you're worried about it just take it out for a squirt more often and boil the crap off while having fun.

It's true what you say about needing a good run, especially DI engines.

[Sabrelli]

How dirty does your oil get when u guys do your own changes.
Im at 5000km now and I checked my dipstick last nite any my oil is darkish tan color.

[kmh001]

Matt I think the analysis is fine. It's natural for the viscosity to increase as the oil ages, in fact it probably got near that value at the end of the boil-off phase around 2,500-3,000 km and the rate of increase tapered off after that.

It's a balancing act to manage increasing viscosity in old oil against the volatility and engine contamination of new oil. But given that we start with fairly thin high-quality synthetic I don't think we would be too likely to enter any danger zones at a modest 10,000km.

I guess it's possible there are issues with RP similar to those we read about in the gear oil analysis, but I wouldn't know anything about that.

As for the question of types of synthetic: I believe it's an issue of comparing polymer performance. At the molecular level, it's the curled-up and inter-twined polymers that physically separate the metal surfaces inside an engine. With exposure to heat and physical pressure the polymers eventually unravel and separate resulting in their failure to keep the metal surfaces separated. From what I've read, I would expect the man-made synthetic polymers to better withstand those stresses and therefore to last longer.

[mav2777]

I got a oil analysis done at the 10,000km interval (car had 50,000km on the clock) & it was all good. According to the report I could have extended it for my type of driving (90% freeway) but I am going to keep changing as per Mazda recommendations every 10,000km & I use Shell Helix Ultra 10W-40.