Doug Hillary

Hi,
Steve - yes effectively M1 T&SUV 5w-40 is the same thing in a non commercial package!

There is no 10w-30 oil that is Porcshe Approved & Listed. This is with good reason as the 150C viscosity is not durable enough for use in our cars!

Incidently I pay $10.50 per litre for Delvac 1 5w-40 here in OZ and I am a Commercial user!

Best of luck, enjoy

m21sniper

"Dave, you can buy Mobil T&SUV at Walmart for $21 for 5 quarts. It's the same stuff in a different package for less money."

Is it synthetic?

And if i may ask, what's 'better' about 5w40 vs 15w50?

I already get about 150+psi of oil pressure at startup, and it pegs well over 100psi at WOT even at full operating temperature.

I'm ALL FOR treating my shark to a better diet, so please explain exactly what advantadge the 5w40 you reccomend holds.

Thanx.

John Veninger

But that's only $7.50 in real dollars

Still expensive. The US really does get "cheap" products made from oil compared to other nations.

John Veninger

What are you using to measure the pressure??

Always drive your 928 "easy" until it warms up. That doesn't mean let it idle real long to warm ir up!

m21sniper

I just installed a triple cluster of VDO 'pilot' mechanical gages.

Oil pressure(0-100psi, pins at about 150psi i guess), water temp(100-280 F), volts(10-18v).

I used a 79 style center console face piece with the round clock hole and drilled two 2" holes on either side of it(i deleted the ugly digital clock).

Came out FANTASTIC, and looks completely OEM.

I'd post pix, but my digicam took a crap the other night. As soon as i get a new one i'll definitely post pix, it makes the interior look much, much sportier IMO.

John Veninger

My accusump gauge shows around 125, cold and idle. Will run up to 135 at 2K. I wait until warm before any real driving on the track.
100 psi, hot and at idle seems on the high side. May want to check the gauge or switch to the 5w-40.
The bypass is factory set at 8bar.

m21sniper

My coolant only runs at 160F fully warmed up on a hot day, hence the extra oil pressure once hot.

I'm sure the gage is accurate(though not to a 'laboratory level'), the whole reason behind going with the extra hassle of mechanicals is to ensure their readings are not affected by the electrical system.

I asked Wally about this via PM earlier today and he told me that running thicker oil than 40w can increase oil pressure beyond the 8 bars, and i do run 15w-50.

FlyingDog

Yes, Group 4 full synthetic. I have two 5-quart bottles of 15W50 that I'm thinking of exchanging for the 5W40. Right now I have synthetic (Group 3) Shell Rotella T 5W40 in the engine. Doug said that the synthetic Rotella T is good oil and is only about $13/gallon at Walmart.

Doug Hillary

Hi,
m21sniper - firstly, all 5w-40 and 15w-50 viscosity oils are not the same!
So for a simple answer, we will assume you mean M1 T&SUV 5w-40 and M1 15w-50
Better is a subjective word - I hope that this briefly explains some of the possible reasons why Porsche recommend the less viscous oil in its engines

1 - The 928's oil pump is a "constant displacement" type (same as most engines). They therefore deliver the same volume of oil per revolution regardless of viscosity or temperature - it is where it goes within the lubrication system once through the pump that matters most

2 - The OP you mention is part of the viscosity issue - high OP does not mean good oil flow especially with cold oil. High OP places the lubrication system into by-pass - diverting significant oil volume directly back to the pump/pan. As well the oil filter handles a lessor than normal volume of oil as it goes into "differential" by-pass when the oil is too viscous to pass through the filtering media. This happens until the oil is above around 60C - maybe higher at higher (say 2500>) engine revs - depending on viscosity!

NOTE 1:
At oil temp of 60C;
M1 15w-50 has a viscosity of 56cSt
M1 T&SUV 5w-40 has a viscosity of 46cSt
M1 0w-40 (Porsche factory fill) has a viscosity of 40cSt
The differences are quite significant

3 - The operation of the valve train's bucket actuators/lash adjusters depends on oil viscosity. Their operation depends on good oil flow and the rapid build/release of oil within the unit - correct viscosity and linear flow characteristics are very important

4 - The time oil remains in the ring pack area is quite critical - it can take up to three minutes or more for oil to enter/exit this area. Thin oil is suspect for wear in this area in some engines, thick oil acts the same way by increasing localised heat build up. Most German Manufacturers have settled on a 0w-40/5w-40 as the best compromise

5 - More viscous oil than is needed actually increases engine bearing wear (more or less depending on use). This is due to the fact that the oil "wedge" in journal bearings operates at self generating pressures way above what an engine's oil pump can deliver. The biggest issue here is oil flow not pressure - the less viscous oil flows better and assists the replenishment of lubricant and cooling
The ideal High Temperature High Shear (HTHS) viscosity in a Porsche appears to be 3.6cSt or above - that is what they demand in their Approval protocols. Around 4cSt is about right for a 928 IMHO - higher than this introduces the prospect of power loss

6 - A 928 engine in reasonable/good condition should show "hot" (after 30 minutes running - oil temperature above 80C) OP of 1.5-3bar at idle and about 4bar at 2-2500rpm. The factory states 5bar at 5000rpm (variously). Oil that shows 5bar at a "hot" idle is probably far too viscous!

7 - As engines age the oil pump's intake screen becomes less efficient due to deposit build up. More viscous oils can restrict flow in these circumstances and many engines of all makes are now failing due to this

NOTE 2:
The above comments are NOT exhaustive and apply to a 928 used as Porsche intended it to be used - racing requires other more specific considerations of course! In a long distance race applications for instance Castrol's R 10w-60 would HAVE to be a prime consideration

The choice of oil and its characteristics is a personal of course. Mobil's M1 15w-50 whilst not technically Porsche Approved (the 5w-50 version is) has probably the best flow characteristics of all such oils. It is a widely used product with a formidable reputation.
With a 928 engine it would be a bold owner who chose to leave the Porsche recommendations "envelope" considering the potential for crank oiling issues

Sorry for the long answer!

John - I wish for real dollars here!! Out trucking Industry is presently in Blockade mode here due to the soaring fuel prices

Matt - yes, Rotella T 5w-40 is a great product at the price

Regards

m21sniper

So in other words you do not reccomend mobil 1 15w50 full synthetic for use in 928s?

I used to use the 5w50 Mobil 1 in my Buick T-type turbo, but i can't find it locally anymore.

And am i correct in interpreting that you reccomend M1 T&SUV 5w-40 for my 928S?

I want to use the best stuff i can, because i do drive the car very, very hard at times.

Thanx very much for the detailed explanations.

Doug Hillary

Hi,
m21 - yes I suggest that you use the 5w-40 viscosity that the factory recommends and filled all 928s with from MY92 onwards. M1 T&SUV 5w-40 is what ExxonMobil in NA recommends for 928s (effectively what I use) but there are other brands such as Shell's Rotells T and etc that are great products too

Regards

BC

That 10-60 Doug - What is the HTHS? Seems very thick. Possibly something someone pushing the power envelope for the 928 engine may want to look into? I have discussed the higher power oil needs of these engines with you before. Your comments are always appreciated.

I'm at 6100 miles now on some T&S 5w40 in my wife's MDX. I was going to get a blackstone or Amsoil test shortly to see how its doing.

I was planning on breaking in my 78 motor (and the 89 motor as well) with straight Penzoil 30wt. I believe we have discussed this as well. The engine will require quite a bit of tuning, so there may be some unsual issues such as too much fuel or lots of reving early on in the engines life - so I wanted to get your opinion on that as well.

m21sniper

Thanx again Doug.

Mobil 1 Truck & SUV 5w40 full synthetic WILL be going into my shark ASAP(i just changed it 3 months ago too, damn!).

Doug Hillary

Hi Brendan,
yes a SAE30 oil will certainly not hurt the break-in process which no doubt will not be "too soft". A diesel rated mixed fleet SAE30 C?/S? or 15w-40 HDEO would work too. I recenty had to run a truck under full load on the dyno for about one hour to seat new technology hard chrome rings that according to MTU-Detroit Diesel may take up to 150k miles to seal! Even though it was started on a mineral oil and had run out to 5000kms without oil use I was concerned as the vehicle is on metro short haul use

Castrol's R (RS?) 10w-60 is ideal in some engines used in long distance racing where overfuelling may cause fuel dilution and a lowering of the virgin oil's HTHS viscosity of around 5.4cSt. Yes, the HTHS vis of this oil makes it too high for our cars in normal use. This oil originally started out as a Castor bean (ester) based lubricant in the 1970s - in use it had that beautiful aroma. Ahhhhhhhhhhhhhh..........!

Blackstone Labs do a great job and have a plethora of Universal Averages across all oil Brands and engine types

Regards

JimBob951

Damn!! I just put $40 worth of M1 15w-50 three days ago!! (and it was the new 12k mile kind too!!)

Jim

87 928S4 a/t
87 951