Fully synthetic or Semi-synthetic oil?

wrote

I still have the

Yes, you can add synthetic to semi-synthetic oil. You could add mineral oil if you wanted. Semi-synthetic oil is exactly what it says- a blend of mineral and synthetic oil.

A bit like the lurid pus-yellow "Egg Shampoo" we used to see in the likes of Superdrug ?

I can think of a certain Anita Bollick (was it ?) who achieved a certain measure of fame by doing the same thing with industrial flavourings and colourings intead of eggs.

DG

From what I've read synthetic oil doesn't need changing so often due to less contaminants being produced so it would be more important to stick to the regular oil change periods if you use semi. For older cars (pre-1990?) synthetic is a no-no since it might destroy some oil seals. Not sure about the oil filter change being extended though!

David Wood (jdwøø snipped-for-privacy@hotmail.com) gurgled happily, sounding much like they were saying :

Crap.

More like a waste of money.

Just another myth about synthetic oils. Mike.

What is the point of them? I heard they hold together better at high temperatures, so good for turbos and racing cars, but for a normal motor, is there much benefit?

Nah, they're a complete waste of time. Manufacturers spec them for fun.

Depends on what car really, and how much you pay for the synthetic oil, and how long you intend to keep it.

The seals thing is that synthetics are generally thinner, so if the seals are a bit dodgy, it can leak past them. It won't damage them.

A wider temperature range (they're thinner when cold, but don't go over-thin when hot), more resistance to cooking and blocking up turbo oilways, better lubrication.

Bear in mind, lots of 'ordinary' motors have a turbo these days. Mine, for example.

Doki wrote

Useful, a well judged intelligent contribution from a ??? (only 8 years and you can get a licence too - you must be excited :-)

I was informed a few years ago by the best engineer I know that fully synthetic oil can be a *very* bad idea in a road going high pressure turbo engine (which I know the 147 isn't). His warranty actually states that if anyone uses fully synthetic oil in an engine he's rebuilt the warranty is null and void - end of story. Semi-synthetic is fine though, almost every road engine he rebuilt had orders to only run it on Shell Helix Plus or similar. As this guy used to build engines for F1 cars and offshore power boats and was involved in oil research with major oil companies I trust him when it comes to oils.

His "No fully synthetic oil" rule came about in the mid 90's when there were a shedload of Cosworths and M3s awaiting rebuilds due to bore wear at his garage. 90% of them had been run exclusively on Mobil 1 which according to the guy in question "piston rings can't deal with, so the bores glaze instead. Then the bores wear and you have to re-bore or re-sleeve the bloody things". Semi-synth doesn't cause anywhere near the same amount of glaze. Basically he was of the opinion that Mobil 1 was ok for some engines, but awful in high performance ones.

"Pete M" wrote in message news:eq4laa$7co$ snipped-for-privacy@registered.motzarella.org...

His point and rule is perfectly sensible and valid during the running-in process which sensibly should last for around 10,000 miles in a rebuilt engine. After that and assuming that oil consumption has stabilised fully, then further wear [because it is essential for wear to take place during running-in] may be stopped or minimised by switching to synthetic. I doubt that the old boy intended the 'no synthetic' policy to last further than the period needed to fully bed-in the new metal components.

Huw