I read so much stuff on the internet about Synthetic Oils that is simply not true so I felt it was time to tell the truth rather than accept the myth.

So in future when you see someone state any of these, please do me a favour and point them at this thread!

Synthetic motor oils damage seals:

Complete Nonsense! Any oil seals made after 1975 or thereabouts will be entirely compatible with any type of synthetic engine oil. (The same goes for synthetic gear oils and transmission oil seals.) It must be understood that everything associated with lubrication is thoroughly tested. The major oil manufacturers do not make oils that attack seals; seal manufacturers ensure that their products function correctly with modern lubricants.

Synthetic oils are too thin:

It is true that the best synthetic blends can be low viscosity (0w-20 for example), but they do not have to be! It is also true that the latest engines are designed to run on thin oil, which improves power output and fuel consumption. Even so, thicker synthetic based grades (10w-50, 15w-50, 20w-50etc) are available for air-cooled motors, older engines, or severe high temperature conditions. These grades can also benefit rebuilt classic engines dating back to the 1940s.

Synthetics mean higher oil usage:

The complete opposite of the truth. Oil consumption in well-maintained modern engines is mainly down to the oil evaporating at high temperatures. Synthetic base oils (specially the PAO and ester types) are very resistant to evaporation loss even in low viscosity blends, so oil consumption is minimised. Obviously, engines with worn valve guides, defective seals and worn piston rings will use oil regardless, so there is no point in using expensive synthetics as an

thanks oilman, more useful info

Hi Simon

Have to agree with the above. I used Mobil 1 since before it was called Mobil 1 in all sorts of engines to high mileage. Without exception, on strip down, the insides are free from wear, retain excellent compression ratios and use virtually no oil between services. As for sludge, the Mobil 1 leaves the internals of the engine with a very slight brown discolouration that wipes off with a finger, where other non synthetics would leave a black sludge or glaze residue. Hydrualic lifters pump out free running as opposed to the gel that a non synthetic will produce.

However, for all the evangelising, there are IMO a couple instances where a highly detergent synthetic can cause problems. For oil seals that have lived a long life fed on dodgy cheapo stuff, you can get a layer of glaze or deposit migrating along the shaft and into the seal area. Now when you run a high detergency oil in these situations, it can wash out the glaze leaving a seal with excessive clearences running on a clean shaft. perhaps this is where the "bad for oil seals" myth originates?

Also, again for old engines with deposits of cack around the oil system, a high detergency oil may lead to the break up of deposits in large chunks. If one of these chunks wedges itself into an oilway at a critical point, damage could result.

Chris

PS Used Mobil 1 in a pan heated up to around 150 degrees is an excellent way to clean engine parts without recourse to agressive chemicals or abrasion.

PPS If you had a Fabia vRS, what would be your favourite oil for it?