[Piers]

Originally Posted by The X Men

This is a quote from an European oil forum. I have read about this in a few other articles. New synthetic oil take a while to set in, changing your oil too often can cause more than good.

"The Problem
5000 km change intervals are harmful to your engine and our DI engines are even more vulnerable to the type of damage done by over servicing than PFI engines.

Why does the problem exist?
It's a cultural thing that arose in the US and was driven by marketing and profit making. The consequent myths and consumer expectations are now entrenched. The cultural gap is now so broad than in the US a car may have an 8000km OCI, while the same model, from the same production line, might have a 20,000 km OCI when sold in Europe where people aren't affected by the myths.

Why it's OK to follow the manufacturers service interval
All synthetic oils are capable of exceeding the manufacturers recommended OCI by at least 50% or more. It's incorrect to suggest the oil could break down or succumb to sludge any earlier.

People using oil analysis reports to justify over servicing aren't reading them correctly. None of the reports that I've seen on DISI engines have shown oil that has reached condemning limits in terms of insolubles and oxidation. As for the solubles, if they are excessive, you need to drive the car further, not change the oil.

The references to carbon contamination are also incorrect. People naturally assume that black oil is unhealthy, when the opposite is true. The colour of the oil is an indication of how well it's doing its job. The darker the better (up to a point not exceeding the manufacturers OCI).

If you had a problem with contamination (not that you do, but if you did) the solution is to change the oil filter, not the oil.

Why is it harmful to change the oil too frequently?

In a word; volatility. Oil volatility is at its greatest in the first 3000km after an oil change. After that the volatility reduces and the oil stabilises.

Volatility is particularly bad for a DI engine because all of the lost fractions exit via the PCV system. Much of it goes out through the rocker cover vent, into the intake, through the turbo compressor and intercooler, then puddles in the bottom of the inlet manifold where it combines with the stuff coming through the PCV valve to coat the inlet valves and combustion chambers in gunk.

That black soot you see in your exhaust pipes, don’t assume it’s all caused by rich mixture. Excessive oil changing will contribute more soot.

The presence of oil in the intake also lowers the octane rating of your fuel leading to detonation.

The NOACK volatility test quantifies the extent of oil evaporation. The test standard - ASTM D5800 - 08 Standard Test Method for Evaporation Loss of Lubricating Oils by the Noack Method – also hints at another kind of danger associated with frequent oil changes where it states “Procedure C, using the Selby-Noack apparatus, also permits collection of the volatile oil vapors for determination of their physical and chemical properties. Elemental analysis of the collected volatiles may be helpful in identifying components such as phosphorous, which has been linked to premature degradation of the emission system catalyst.”

A lot of phosphorous is lost in the initial boil-off phase of new oil and it’s likely to be harming oxygen sensors and cats.

Engine manufacturers understand the problem and it would be easy for them to identify the type of damage done by over servicing and potentially result in a warranty claim denial.

Summary
By changing your oil at 5000km, you are subjecting your engine to oil that is almost always in the initial boil-off phase. It's contaminating and filling your engine with gunk. Contrary to popular and uninformed opinion, oil that is 10,000 km old is not likely to be harmful, and would certainly be less harmful than fresh oil.

I've never changed my oil more frequently than the specified 10,000 km OCI and my engine is in perfect condition after 106,000 km with no problems with contamination, gunk or soot.

When my warranty expires I would have no qualms running my oil out to 12,500 or even 15,000 km providing an oil analysis indicates that insolubles and oxidation are not excessive. And I'm sure my engine will thank me for it by remaining in peak uncontaminated condition."

That will put the cat amongst the pidgeons for some of the responses on this thread then