ROG100

The spec sheet from Porsche was compiled in 2004 long before some of the current legislation/marketing removed Zinc from current oils - so is the info still current???

the flyin' scotsman

Roger.........is Royal Purple synthetic?

When using mineral oil I'm a 20W50 guy also but I've running a variety of Synthetics over the years in the 928; Mobil 1, Castrol Syntec, Penzoil and without taking the engine apart don't notice much difference. Viscosity numbers I keep to around the same as the dino stuff theory being she doesn't get driven in 'cold' weather but does during the 'hot'.

Bill Ball

This is a murderous subject. Use whatever makes you happy.

IcemanG17

This is a good point.....it all depends on how you drive the car and the weather where you live.... If you live somewhere very hot & do ORR.....then 5-40 is not a good choice.... If you live somewhere fairly cold and just cruise around....5-40 should be fine....

IMNSHO.... I used mobil one 15-50...then switched to Amsoil racing 20-50, since I occasionally do DE's and autocrosses

Bill Ball

Dou Hillary has made his very educated arguments for Delvac 5-40 regardless of high enviromental temperatures and funky idle OP readings. It's hard for some people to accept, including me. However, I don't think any of us can refute what he has said. None of us are petroleum engineers, so you either accept his advice or you don't.

Mike Frye

Bill and everyone,

I wasn't trying to rehash the oil vicsosity issue or brand here. All I was trying to bring up was that the 1.5 bar seemed low. I never see mine that low.

I guess my question should have been:

Is it normal to run 1.5 bar at idle? I don't know, all I know is what mine does and what (I think) I've read here. If 1.5 bar at idle is normal and acceptable then there's no issue. If that's low, then I think it bears scrutiny, since the consequences can be very bad.

I'm sorry if I wasn't clear in stating this earlier. I wasn't trying to say anything, rather suggesting that this seemed low.

ROG100

Royal Purple is readily available here in DFW and used by many of the local race guys (porsche cars). Its synthetic and comes highly recommended and I am going to use it because it meets ALL MY criteria for MY car.
Bill, I agree with you 100% but Delvac did not cut it for my car as the OP light comes on at Hot Idle. Never a problem before I switched from Mobil 1 15W 50 to Delvac. No matter how good Delvac is I cannot sit in traffic with my low OP light on - no way - it just makes me uncomfortable. Now that Mobil 1 has no Zinc in it for wear protection I do not want to go back down that avenue in the long term.

The key issue to me is I need an oli that works and since no one will tell me what to use I have to make a decision based on the information available to me. Even if someone would tell me what to use there are no guarantees.

ErnestSw

Let me see if I can add some information to the thread. Coming from a medical background I'll use blood pressure as an example.
Blood pressure is a measure of the resistance to flow of a blood, a relatively high viscosity fluid. The blood pressure is measured at a major artery ie. the brachial artery and would be slightly higher at the aorta. As the vessels narrow there's a progressive drop in pressure until you get to arteriolar pressure.
The anatomic analogy is between the brachial artery and the line from the oil pump and the arterioles and the smallest oil passages in the engine.
If you change from very viscous blood to very thin kerosene the amount of pressure at the heart required to maintain the same level of FLOW in the arterioles would be less. Likewise, when you reduce the viscosity of oil you can maintain the same amount of FLOW in the smallest oil passages and still have adequate lubrication.
That STILL doesn't answer the question as to why some cars show low oil pressures with Delvac and some don't. And why mine has and doesn't any more. Could it be that the springs take a "set" with the greater pressure of the higher viscosity oil and don't respond to the lower pressure accurately?
Changing the spring would be the only way to find out.

dr bob

There's a good point with the oil pressure vs viscosity index vs oil flow, BUT... There are multiple flow paths for the oil in the engine, and some of those MAY require more pressure than others to maintain the correct flow. Sometime around when the engine was designed, a hydraulics study was done where each path was analyzed for pressure and flow. OK, maybe not. Still, I'm of the (sometimes feeble) mind that if I can keep the pressure in the originally-recommended range, using an oil viscosity that is in the originally-recommended range, I'm likely to achieve flow in the originally-recommended range through all of the intended flow paths inside the engine.

So for me, the 15W-50 Mobil-1 seems to do the job just fine. YMMV, of course.

Bill Ball

I didn't mean to be accusing you of trying to stir up the hornets' nest. You don't need to. Just mentioning viscosity does that. 1.5 bar is fine at hot idle. Doug even went further than that when this was brought up, but I don't want to misquote him. I'll poke around for his comment and link them. Many people get nervous here with low OP on hot idle. Unless the warning light comes on, I can't see why. There is no idle pressure specification that I can find.

ROG100

Bill,
Thats my issue - both Jim M and I changed to Delvac at the same time and both went from good OP to not so good. I would be happy with 1.5bar - however 1bar and the OP light make my sphincter twitch little.
Not trying to stir anything at "oil" - live from DFW.
Roger

Bill Ball

AFAIK, the warning light is zero pressure [correction: Doug says the switches are typically 0.5-0.75 bar]. If I saw that, I would get excited too. The spec for oil pressure is at 4000 RPM, and I can find no spec for idle, but zero wouldn't seem too good. Anyway, I had that warning light come on after a very hot open road race as I pulled to a stop at idle. I was trying some Castrol Syntech 5-40 in place of my regular M1 15-50. As soon as I saw the warning light I killed the motor and waited 30 minutes until it cooled of considerably. After that it was fine, and the car seems none the worse for it. I decided not to use that oil for open road racing, even though I believe Doug argues that a transient flicker of teh warning light after a hot run is common and not significant. I'm looking for an oil with low cold viscosity to reduce time on bypass but with adequate high temp viscosity so the warning light doesn't come on, but that's just my layman's interpretation of what is good for the car. It seems just about any oil meets that stated OP spec at 4000 RPM. Many don't meet the HTHS spec.

Bill Ball

Of course, I forgot the necessary caveat - the OP meter and the OP warning are notoriously inaccurate.
https://rennlist.com/forums/showpost...85&postcount=4

Bill Ball

Here's some of Doug's comments about the hot idle OP and switching to lower viscosity oils.
https://rennlist.com/forums/showpost...2&postcount=45

ELJG

As a newbie (only had my shark for 1 year) I have read everything I could and sought all the advice, so I'm naturally confused! I have only ever had the low warning light on once and that was because the car was parked on a steep incline. I am not aware of any problems but recently I got to wondering: is it ok to have a pressure of 4 bar from 2000 rpms on? The idle is steady at between 2-3 bar. Obviously when hot. The car was previously serviced by an independent (used Magnatec) , but last oil change was done by Porsche dealer. They recommended and put in Mobil 1 15-50. Car is a 95 GTS.
My question: is 4 bar at 2000 rpm ok? Thank you for any info/advice.