Charles Navarro

Good advice. But as far as being cheaper, the group 3 royal purple racing 21 for example is about 75% more per quart than M1.

DGaunt

Hey Doug,

Are you on the TDI list too, or are there two guys in Austrailia who are car nuts and own a heavy truck operation? Wait, I probably know the answer to that one: "Only Two?"

anyway, It might simplify my life too, to use Delvac1 in both cars. but I have one last question: I use the 20W50 oil to help maitain iol pressure especially at idle; a well documented flaw in the 2.7 911 engine. I have upgraded the pump (to SC) and the engine has only a few thousand miles on a rebuild, and with the cam restrictors installed will hold a good 20 PSI at 190 Deg. oil temp @ Idle.

Do you think I CAN run a 5W50 and maitain acceptable iol press. at hot idle?

Thanks for all the great info.

Doug Hillary

Hi Dave,
yes Dave I am on the VW TDI board and once worked for VW in New Zealand and in Denmark. My wife has a MY02 Golf - the TDI is only now being sold here as selling diesel cars here is like selling chocolate teapots!

The issue of pressure and flow is vexed

Oil pumps are constant displacement per engine rev and the pressure simply a measure of resistance. Sort of like pumping oil into a telescopic aerial I suppose as the internal friction increases pressure and changes flow characteristics but maintains volume (subject to nornmal losses en-route)

Most synthetic oils have very much better flow patterns than their mineral equivalents and even Mobil say to expect a pressure loss at low revs - flow (volume) is the same and the end result is a benefit in cooling alone

The insufficient oil pressure lamp trigger point of less than 1bar (about 0.75bar) tells the story and in most engine families about 1.5-2bar at idle is enough - remember that the flow is constant and the engine is not under load

Porsche's minimum oil pressure requirements are given like most German makers makers - the specified viscosity oil @ 80-100C at 4000rpm - is typical. The 928 needs 4bar (some 5bar) and so do most 911s I believe

The 5w-50 oil will be an excellent choice I expect as it is the "50" viscosity rating at 190F that determines the idle oil oil pressure. At 93C M1 5w-50 has a viscosity of 20cSt against its 100C viscosity of 17.3cSt - a typical 20w-50 oil's viscosity at 93C would be around 23cSt

Regards
Doug

DGaunt

Thanks again, Doug. Thought it was you...great to have access to knowledge such as yours.

One last question, if I may:

How would Mobil 1 and Delvac 1 compare in (can never remember the technical term) its ability to "stay were it's put" EG: when i store the 911 for 3-4 months (imminent now) which oil will stay on the internal engine parts longest, providing corrowions control and 1 st start protection?

TIA

Doug Hillary

Hi Dave,
of the two oils you mention (M1 and Delvac 1 5w-40) Delvac will be somewhat better at the "stay where it's put" task

Any mixed fleet HDEO will handle the "storage, idle engine" task better than a normal petrol engine oil will

There are specific storage formulated HDEO oils that are used in the Agricultural Industry, these have a Vapour Phase Inhibitor (VPI) additive. The VPI additive works by emitting a corrosion inhibiting vapour to passovate metal surfaces and protect exposed parts above the oil level. When using these oils it is best to use on the road for 200 miles or so before storage. They can then be used again for a week or so at the end of the storage period before putting your normal oil choice back in

There is a myth that synthetic oils do not stay put as well as their mineral cousins. If they both meet the same quality standards most synthetics will out perform a mineral oil in the task. HDEOs do it better!

Regards
Doug

84_Carrera

Doug, one thing I'd like to add is my own observations in working on Ford Taurus SHO V6 engines... I've personally found that Castrol GTX tends to "cling" to the overhead cam surfaces longer than M1 does. Now, the last time I pulled an M1 engine apart after longer sleep periods was about a year ago, perhaps their newer formula is better along those lines.

Notes from the field anyway.

Doug Hillary

Hi,
Fred - yes observations are always helpful. The M1 SuperSyn formulation is great but I cannot comment from the "cling" perspective

Lubricants use various chemical measures to cover the potential metal to metal risk and these additives range from those that "plate out" to simple polar attraction. The risks of scuffing etc caused by dry starts after short term storage when using a modern engine oil are cery remote indeed

I use 5w-40 synthetic oil because it has a very low pour point and excellent pumpability at start up. As well the synthetics with lighter low end grades (0w or 5w) overcome the differential pressure of the filtration media much sooner (at a lower temperature) and go off by pass sooner

Castrol here in OZ market a Group 3 semi-synthetic oil called Magnatec - it was once called GTX Magnetic. It claims "Unique Modular Attraction" (UMA) and has been the subject of a Legal defintion but advertising sure hits the edges of reality at times!

I hope this makes sense

Regards
Doug