Thin oil for Porsches.....live 'n learn

Pennzoil motor oil
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Bill888

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I've been restoring aircooled Porsches for over 40 years and have always used 20-50 or straight 30 or 40w in the older 356 cars. I've kept away from the new thin oils because these oils worked for me over the years - and I therefore had no need to experiment with the newer viscosities. However, reading the April edition of Excellence Magazine (Porsche) there was an interesting response to a Boxster owner concerned about using the Porsche specified 0-40 oil. The response by Bruce Anderson, a longtime Porsche expert highly respected in the community, was that certain systems rely on a specific viscosity oil for purposes other than lubrication. The Vario-Cam system is one (the others mentioned were engine cooling and the hyd. lifters.) He cited a Porsche technician who spent hours trying to diagnose a poor- running car. Turned out to be a higher viscosity oil causing the problem in the Vario-Cam system!
While I won't be putting 0-40 in my old Porsche just yet, I'm realizing that what's good for "older" Porsches doesn't really apply to the requirements of the newer ones.
Bill.
 
Well, the oil is very different visc at different temps. Hard to imagine that only at a certian temp/visc the engine would function properly.
 
Air cooled engines very much need a 50wt oil to run properly... and yes, vario-cam does work based on oil pressure as one of the variables so oil viscosity is extremely important in more technological engines.
 
I agree, air cooled and water cooled are different beasts - both in terms of temperatures and manufacturing tolerances.

If I had an air cooled, I'd run a good 40 or a 50.

When I had a water cooled 968 with Variocam, I ran Mobil 1 15W50 until the very last OCI before I sold it where I switched to Mobil 1 0W40. Variocam worked fine with both, but I liked the feel of 0W40 better. The 15W50 was very "heavy" feeling. After learning about Mobil 1 0W40 shear issues here, I'd probably run some other 5W40 or 15W40 that wouldn't shear if I still had the car today.
 
IMHO there shall always be fundamental differences between water-cooled and air-cooled engines:

-in water-cooled engines, water jackets take care of at least 75% of the waste heat from combustion process, leaving the remaining 25% into metal thermal conduction, lubrication system carrying the heat away (cylinder wall, underneath side of the piston crown, etc.)

-in air-cooled engine, 10% of the heat is to be "wick" away by thermal conduction; the remaining heat is to be approximately split 1/2 and 1/2 by air cooling (cooling fins on cylinder heads) and lubricating oil.

With the exception of early british cars (which I don't have enough experience/understanding all along), most air-cooled engines started their life with single weight 30 or 40wt oil (citing air-cooled VW around early 50s) and when shear-stability of multi-vis oil came into pictures in the 60s and early 70s, builders and operators been up in wt to 40s, 50s respectively.

Now, with lots of shear-stable multi-vis oul available OTC, I simply cannot see the reason to stick/stay on with 50Wt oil in air-cooled engines, and I'm willing to lower it down to 5W40, 0W40, 0W30(winter time, full sync, operated below -30C ambient) if I were you.

Just my thoughts of this subject. Had an old funky 1300 VW in the past.
 
The SAE Automotive Handbook clearly states that oil viscosity has no effects on variable cam systems. This makes sense as oil viscosity varies a thousand fold depending on the oil temperature. Two cS difference at 100 C temperature is irrelevant. I would not think that the person who said it does matter - well their knowledge level is suspect.


aehaas
 
Quote:

The SAE Automotive Handbook clearly states that oil viscosity has no effects on variable cam systems.

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With all due respect to the SAE, I think I'll take the word of the engineers who design the engines on this one. Chrysler specifically states that 5w20 is required for the MDS of the Hemi to function properly. I would not be surprised if Porsche has the same vis requirements for their engines.
 
With respect to variable cam systems, I have personal experience with system malfunction attributed to a heavier-than-specified oil. This was on a 98 Ford ZX2 Duratech engine. Switching back from 20W-50 to 10w30 made the problem disappear immediately.
 
I have a garage full of toys. One is a '89 Porsche 911. Based on all I've read I'm sticking with conventional 20w50 oil in the 911. I've read the LN Engineering story and agree with him.

Now in all of my other cars which are much newer and all that. I'm using synthetics in the rating and weights called for.
 
The most current TSB from Porsche has many approved oils listed....There is only 1 that is a 50 weight, Mobil 1 5w50. I havachieved the least wear in my 911's using either Rotella/Delo 15w40 in the street cars or Redline 10w40 in the race cars. Using a 50 weight did not decrease wear, in fact in the race cars it increased my oil temps.
 
Please people, teach me. A 40 wt. oil has a viscosity of 3,000 at 10 F, 14 at 200 F and 3 at 300 F. What is the correct viscosity for the cam actualtor to operate properly, just give me the number. I am not that bright, explain this to me.

aehaas
 
Quote:

Please people, teach me. A 40 wt. oil has a viscosity of 3,000 at 10 F, 14 at 200 F and 3 at 300 F. What is the correct viscosity for the cam actualtor to operate properly, just give me the number. I am not that bright, explain this to me.

aehaas

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For the sake of argument, let's say that Chrysler's MDS in order to operate properly needs a vis of between 4.0 and 10.0 when the engine coolant has reached a temp of at least 185F and the oil temp has reached a temp of at least 150F. Let's say it's designed that way. Let's further say that the MDS won't operate at all until the coolant is at least 185F. The operating range of 4.0 to 10.0 assures the MDS will function properly using 5w20 at oil temps from roughly 150F to 250F, which would cover about 99% of all driving conditions the average driver will encounter. Now let's throw some 0w40 oil in there. Will the MDS function properly on this oil? Yes, but only at oil temps above 250F which the average driver is likely to see only 1% of the time.

NB the above numbers are for illustration purposes only and are not meant to be accurate. But I do believe they reflect what is actually going on with variable valve timing and cylinder shutoff systems that require certain oil flow and pressure parameters to operate properly.
 
some of the porsche, praticularly the 914 has a thermostatic oil cooler flapper that worked on engine temparture. when the engine warmed up it opened the duct to the oil cooler to let air pass through. this car also had a oil pressure related oil cooler valve. if there was too much pressure the engine wouldnt let oil flow into the oil cooler. i dont know why it was like this but i guess the factory thought that they could mearsure engine engine temparture by oil pressure. when the car warmed up the oil pressure dropped and the oil cooler started working.

what you got was in certain instances people overheat the engines running thick oil. the oil pressure of the thick oils never got low enough to let oil flow through the cooler.
i cam remember a guy with a fresh tight 914 motor running a straight 70 weight and his motor got so hot is was smoking. i guess that guy learned his lesson about using overly thick oils.
the sad part is that guy was me.
 
Quote:

968 is a fat car.

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Erm, I don't know how to respond to that.
dunno.gif


I do know that the 968 makes a heckuva lot of heat that's removed by all possible manners. It's a 3.0L *4* cylinder with 11.0:1 compression that requires 93 AKI fuel. It made a lot of heat, especially at high revs. It used forged pistons and rods and had a piston-cooling oil jet system. The oil was cooled by a thermostat-controlled ducted air/oil cooler in front of the front/right wheel.

Everyone recommended I stick with a 50 weight and once it was up to temperature it was fine. Mobil 1 0w40 (in early 2000s it became recommended by Porsche for all cars) resulted in a more "normal" feeling engine response, better throttle response etc... when anything but HOT. Mobil 1 15W50 stayed crystal clear through an OCI - no other grade of Mobil 1 in any other car I've had was able to do that. Yeah, yeah, colour means nothing but that's an interesting observation.
 
Quote:

The SAE Automotive Handbook clearly states that oil viscosity has no effects on variable cam systems. This makes sense as oil viscosity varies a thousand fold depending on the oil temperature. Two cS difference at 100 C temperature is irrelevant. I would not think that the person who said it does matter - well their knowledge level is suspect.


aehaas

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The problem isn't at operating temperature, it is in cold weather at startup. This happened to BMW in the early 90s when they introduced the M50 engine which used variable valve time driven by oil pressure. Owners in cold climates would complain the car missed horribly when starting. Turned out it was from dealers using 20w-50 (which they shouldn't have been even for non-vanos engines). By going to a 5w30 during winter, this fixed the problem.
 
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