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Discussion Starter · #1 ·
currently using Mobil-1 5W-50. can i replace the oil and filter at 10K kms instead of 5K kms?! alternatively, must i use fully-synthetic oil for turbocharged engine?! was thinking of using Castrol Magnatec 10W-40 (semi-synthetic oil) and replace the oil and filter every 5K kms, this seems to be cheaper in the long run!! what do you think?!

Discussion Starter · #2 ·
This is a mucho discussed subject. Here's my 2 penneth.
Always use a full synthetic oil with a turbocharged car. The temperatures the turbo reach are much higher than a conventional non-forced induction engine. Normal mineral oils breakdown at much lower temperatures than syntheitc oils
leaving carbon deposits in vital oilways , such as the turbo oil feed, causing bearing starvation and turbo failure.

Next, is what weight/viscosity to use. I use 15W-50 Mobil1 for the protection it gives the engine at higher temperatures ( Castrol RS10W-60 is good one also ). Some use lower w numbers and or semi-synthetics,
because there is an argument that the hydraulic tappets suffer from use of the heavier oils.
As I understand it, the W number is related to the viscosity and how well the oil flows at low temperatures,
and the second number is how well the oil protects at high temperatures.
My reasoning is that it is better to have a top end rebuild than a bottom end one so I use the heavier oil.
Having said that, my e6 engine has covered 47k miles and although the tappets do rattle sometimes when cold,
I feel that my engine is in good shape, that is, it still pulls like an express train border|EQU| 0 align|EQU| absmiddle >

Some on here have tried Magnatec since it was recommended by Coordsport/Ralliart and have found it to give Tappet
rattle, others have had success.
Magnatec is significantly cheaper than Mobil1 or Castrol RS, but it is based on a different synthetic technology
it may be even semi-synthetic.

My recommendation (there are no kickbacks from Mobil for me [img] border|EQU| 0 align|EQU| absmiddle >) is Mobil1 Motorsport 15W-50

Discussion Starter · #3 ·
The slightly thicker synthetics (Mobil 1 15W-50 or Castrol RS 10W-60) will reduce the hydraulic tappet rattle. The thin stuff (0W or 5W) just drains back out of the tappets and leaves air pockets if the car is left standing for a while (esp. if on a sideways slope).

I have switched from Shell fully synthetic 5W to Castrol RS 10W and have noticed significant reduction in tappet rattle.

I'd rather run a slightly longer oil change interval than use anything other than fully synthetic. In an old copy of Car Design and Technology magazine there was an aircraft maintenance engineer who had run his Saab 900 Turbo over 60,000 miles on the same Mobil 1 oil with extra bypass filtration fitted. he used to test the oil in the lab at every oil change instead. The bypass filter keep it cleaner.
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