Synthetic oil for I-5s

[Robert Deutsch]

David, I'm just finishing up my mechanical engineering degree and I've
been talking to the profs at school lately about this.

First off, synthetic oil may not give you any cooler oil temps (the only
way it would be cooler is if the oil had higher conductive and
convective heat transfer coefficients - which would probably be
negligible - and then the limiting factor still remains the heat
transfer properties of the engine block, valve cover, and oil pan).

As far as changing from synthetic to dino oil, there is no compatibility
issues whatsoever. You can run a mixture of the two if you like. The
synthetic molecules all being perfectly uniform in size however, gives
you a better chance of leaks; whereas the dino oil has a range of
molecule types and sizes which can build "beaver dams" around areas of
potential leakage. If you suspect leaks, you should use the highest
viscosity synthetic oil you can find (ie: the higher the first number
the better - 10 from 10w30 for example). Watch out for oils like 5w50
synthetic. When cool it acts like 50 weight oil, but when up to running
temps it acts like 5 weight (really thin). Try to find 15w- or 20w-
synthetic oils for higher viscosity at high temperatures.

As Jim mentioned, if heat is seriously a problem, the only way to
properly deal with the heat is with an oil cooler. This is an additional
radiator that will remove the excess heat directly from the oil.

I personally just had to go back to dino oil as I couldn't find
synthetic thick enough and my valve stem seals are starting to fail. I
went back to 20w50 multi-grade and it has resulted in less blue smoke.

Rob Deutsch
'90 CQ20v 200k
'01 Beetle Turbo Sport 20k




> From: David ?duandcc_forums at cox.net?
> To: quattro at audifans.com
> Subject: Synthetic oil for I-5s
> Date: Tue, 19 Aug 2003 9:13:53 -0400
>
> I've been running 20W50 dino oil in my CGT and doing MMO treatments before =
> oil changes. I was thinking of switching to synthetic for it's cleaning pro=
> perties and to help keep oil temps down (in high speed/agressive driving on=
>  the highway my oil temp goes as high as 150*C, cruising is around 130*C an=
> d in town around 90-100*C). I realize there is a chance that the synthetic =
> will clean out the engine so well that it will begin to leak or burn oil. M=
> y plan was to switch to synthetic for 6 months or so to clean it out then s=
> witch back if it leaks or consumes oil. So, what are your thoughts on this?=
>  What weight is appropriate for I5s? Is it available in 20W50? Do I even ne=
> ed it that thick with synthetic?
>
> Dave
> 2002 Jetta 1.8T (hers)
> 1993 RX-7 R1 (weekend play toy, soon to be for sale)
> 1987 CGT Special Build 2.3
> in SE Virginia