I can't speak for the Porsche, but I've heard the same claims made about Honda's variable valve timing system--i.e. that the system requires a certain viscosity to work correctly. But that simply isn't true. It's true that the valve timing is actuated hydraulically, but the position of the cam is determined by a cam position sensor. So the sensor closes the loop, not oil pressure. It has to work that way because of the huge swings in viscosity as oil warms and cools, as AEHaas correctly points out.
Thin oil for Porsches.....live 'n learn
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My 2001 Porsche originally came with 15w50 M1. This oil reportedly caused some ticking problems when very cold, so porsche changed the reccomendation to a thinner oil. I believe the noise came from the variable valve LIFT mechanism more then the cam timing mechanism.
Well, I knew that, but without the gestures and crooked ballcap it was hard to tell.
Of course, we both meant "phat".
Maybe he means: "phat"???
On a serious note, I also don't believe the 'needs a certain viscosity' to work right thing since (as was pointed out) visocity is temperature dependent there are huge fluctuations in viscosity with operating temperatures and seasons.
On a side note....if air cooling is so dependent on oil for cooling, shouldn't one be using 0-10 in these engines?
Funny on the BMW quote too...guess the VANOS isn't working in Europe (or the rest of the world) since they're not using a 5-30.......
On a serious note, I also don't believe the 'needs a certain viscosity' to work right thing since (as was pointed out) visocity is temperature dependent there are huge fluctuations in viscosity with operating temperatures and seasons.
On a side note....if air cooling is so dependent on oil for cooling, shouldn't one be using 0-10 in these engines?
Funny on the BMW quote too...guess the VANOS isn't working in Europe (or the rest of the world) since they're not using a 5-30.......
Air cooled engines are dependent on oil for cooling, but from my understanding there are lots of temperature variations throughout the engine. These variations are much greater than when the block is filled with coolant helping to even things out a bit. For that reason, I've read (in Porsche technical magazines) that clearances are larger than water cooled engines. The super-hot spots combined with the possibility of great tolerances leads to thicker oils in air cooled engines - particularly the high performance (ie. Porsche - not original Beetle
variety. Not to mention the "designed" usage of these engines - racing at WOT.
Apparently on the 944/968 cars, high temperature idle oil pressure would drop so low when 30 weights were used that they'd be
In the early and late driving seasons, sometimes the temperatures would be around freezing. Once I remember having to start the 968 only to move it out of the way of my parents' car when we were visiting for the weekend (I always hate short starts like that). The oil pressure continued to be pegged for a couple of seconds after shutting off the engine, then slowly fell to 0 over an additional 5 seconds. TOO THICK
Not sure what 'flexible' part of the oil system the pressure was retained in - hoses? filter and housing? I've always wanted to show a video of that to the folks yacking about 15W40 "pour points" of -X C and how we shouldn't worry about it. My story was about -2C I believe. That's another reason I switched to M1 0W40 at the end.
Apparently on the 944/968 cars, high temperature idle oil pressure would drop so low when 30 weights were used that they'd be
In the early and late driving seasons, sometimes the temperatures would be around freezing. Once I remember having to start the 968 only to move it out of the way of my parents' car when we were visiting for the weekend (I always hate short starts like that). The oil pressure continued to be pegged for a couple of seconds after shutting off the engine, then slowly fell to 0 over an additional 5 seconds. TOO THICK
"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."
It is quite possible that for a given variable cam system some oils might be too thick when cold or too thin when hot. Yes the engineers design for a range of viscosities, but there are going to be upper and lower limits to that range.
The idea that someone (SAE) could unilaterally declare that viscosity doesn't matter to variable valve timing systems is just silly. A straight 40 weight oil might easily be too thick at 10 F for some variable valve timing systems to operate correctly. Heck, some hydraulic lifters would be chattering like a sewing circle under those conditions.
It is quite possible that for a given variable cam system some oils might be too thick when cold or too thin when hot. Yes the engineers design for a range of viscosities, but there are going to be upper and lower limits to that range.
The idea that someone (SAE) could unilaterally declare that viscosity doesn't matter to variable valve timing systems is just silly. A straight 40 weight oil might easily be too thick at 10 F for some variable valve timing systems to operate correctly. Heck, some hydraulic lifters would be chattering like a sewing circle under those conditions.
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