yeaaahhh another summertime oil debate ! (LOL)

I'm looking for some advice here. What experience is there with these 3 flavors of fully synthetic oils:
10w60 (like Castrol) - racing oil, reasonable for when engine is cold, thickest at high temps, shear resistant, better wear protection and best pressure when hot?

5w50 (like Mobil 1, Valvoline) - racing oil, good wear protection when cold, also very good at  high temps, good shear resistance ......

0w40 (like Castrol, Mobil 1, Valvoline, Shell) - good generic purpose oil, good wear protection, thinner for cold starts and lubrication when cold, better for fuel economy, but less thick when hot which may/will cause less oil pressure.

I'm under impression that oil flow is a lot more important for heat transfer and wear protection than oil pressure up until the point where pressure loss causes too little flow or lack of oil in critical places. I presume this point is 1 Bar at 600 rpm. Is that right?

How about 5w40? What is best in a 928s4/gt/gts??
1988 928s4 cherry red
The Netherlands

Hey Theo,
I use Mobil 1 15W50 synthetic in my shark, as I don't run the car in cold weather. So far no complaints, as I have good oil pressure during hot track days. To the best of my recollection, I get about 2 bar (maybe a tiny bit more) at 600rpm when hot. At 3000rpm, I'm reading 5 bar. At higher rpms, the needle goes a touch above 5.

I used 5W40 synthetic for one season, and oil pressure would dip below 2 bar at 600rpm on warmer days (25C and above). That really concerned me, so I switched to 15W50. Takes just a touch longer to warm up.

Paul Gotter


Don't like Mobil 1 at all. Leaks through new gaskets and more head noise after long periods of inactivity than others.

RE: oil: 20-50 is best for all around everything other than winter, I have tried all synth brands at this point, all better protection than dyno juice. If you don't drive your car hard at all you can get away with slightly lighter oil but why would anyone want to do that?
When was the last time we had the great oil debate?

I thought it was the right time for a summer oil debate, but I did put in a few new parameters this time. ;-)

Seriously: 20w50 and 15w50 are the ones heard. Eric likes all Mobil 1 oils (maybe Eric owns Exxon-Mobil stock shares).

Seems thick to me but it is true:
this is what the cars are made for initially. Others claim 0w40 as adequate juice for a 928. I would be interested in experience with 0w40 and 5w50.

I run 15w40 at the moment. 2 bar at 600rpm when hot. 5bar at 3000 rpm when hot.

Hi Theo: My car is very happy with Castrol Syntech 5W-50, but it is strictly a street car. 2-3 bar when hot at idle.
Theo, you should also know that I previously used 20W-50 mineral oil (Castrol) in my car. I live in the northern USA (Wisconsin), and my car goes into winter storage December-March. But the mornings can be cold (25 or 30 F) in April and November. The engine sounds better since I changed to 5W-50 synthetic oil -- less metallic noise -- when cold or hot. But I am not an oil expert.
Bill Schmaal 87 S4 A/T


0w40 Mobil 1 guinea pig.
2 to 2.5 bar at idle. By 2200 revs she's at 5 bar.
Can't run her too hard in this heat till I fix the fragged alternator belt.
But mine's too often driven to get to develop valve clatter noise from prolonged drain-down.


At 12:26 +0100 06.28.06, Theo Jenniskens wrote:
>... I'm looking for some advice here. ...


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This is an interesting contribution to the idea to use thicker oil and thus prevent cam lobe and bearing wear: