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Oil pressure for synthetic oils

Hi all,

i have an 1985 Euro 930. I have been using Pensoil 20w50 (yellow bottle) since the previous
owner and mechanic swears by it. Recently had an oil change and my current mechanic suggested to try the Redline Synthetic 10w60. He has heard great things about it so we tried it out.

One thing I noticed is that the oil pressure seems to read a bit lower than before, especially when the engine is warmed up.
With the new oil, Druck Press reading
COLD:
1000 rpm = 2
2000 rpm = 3
3000+ rpm = 4-4.5
HOT:
1000 rpm = 1
2000 rprm = 2
3000 rpm = 3
4000+ rpm = 3.5
5000+ rpm = 4

I am pretty sure with the Pensoil it was reading 5 when 5000+ rpm.

I have done some reading and people say that synthetic is so much more "fluid" and higher
viscosity that you normally get lower oil pressure readings.

So my question is, what is more important, oil pressure or lubrication viscosity?

Some people even went back to regular oils.

My engine has 130,000 miles, but the previous owner actually had an engine rebuilt at 120,000 miles so the engine is relatively fresh in top end (new pistons, valves, etc).

What do you recommend? Should I go back to Pensoil 20w50?

thanks!
Old 02-04-2014, 01:09 PM
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I can't really give you an answer regarding pressure 'v' lubrication viscosity, etc, but one additional point to consider is an oil's flash point . . . I can't quote numbers from memory, but synthetics are documented to have much higher flashpoints than non, or partial, synthetics and are thus much less likely to coke in the turbo bearing cartridge after shutdown.
Old 02-04-2014, 01:30 PM
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Pressure(as in oil) is really a measure of flow, or rate of flow past a 2-dimensional point.

What your seeing at start-up and when running is the synthetic flows a bit better than the regular oil, however the modern syn's may not have the zinc/phos required for the earlier engines.

I run half syn/half regular(fully compatible to mix) of 20W-50 Castrol/5W-50 Castrol syn to get the perks of both oils, and never run anything but a factory oil filter.

I imagine in Vancouver you don't see the heat like So Cal or the Mid-West, so that's to a turbo's advantage.
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Old 02-05-2014, 11:05 AM
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10W60 is a poor choice for your Porsche. The 10W part indicates the viscosity index under winter test conditions (-20C). The 60 indicates the viscosity index under warm conditions (100 C). The larger the viscosity index number, the thicker, or more viscous the oil is.

The 10W part is OK, but I don't think it gets that cold where you are, so 20W would be OK also. The 60 weight at 100C is a problem. That weight is not recommended by Porsche for your engine. It is too viscous, which reduces the effectiveness of the piston cooling jets. It's not like it is going to blow up or anything (Porsches are designed to take a lot of punishment), but it is outside of the "normal" range. Under extreme conditions it may even start to open the oil pressure bypass valve, which is not good.

I think for your climate, 10W-50 or 20W-50 would be good. The oil pressures that you noted are fine, but I am concerned about the lower oil pressure at 5000 rpm, as that could indicate that the bypass valve is starting to open.

I would encourage you to use a synthetic, as it will prolong the life of your turbo, and help keep your piston oil cooling jets clear.
Old 02-06-2014, 06:19 PM
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Oil pressure and proper oil for 930

Hi guys, thanks for the responses! Much appreciated!

@Tilicum Turbo: the Redline Oil is well recommended by my mechanic and it's enriched with Zinc which is why I would like to use it, but the 10w60 viscosity rating and the oil pressure is what's making me think otherwise.

@Speedy Squirrel: thanks for your explanation. So does that mean that the 60 in 10w60 would be thick oil even when the engine is warm/hot? I am still not quite understanding that when hot the pressure would go down if the 60 oil is thicker than 50 oil... my limited understanding of oil pressure physics would be that I'd want a thicker oil so that it would keep higher pressure. Your explanation of the bypass valve: does it kick in when the engine thinks the oil is too thick so it tries to make the engine "flow" better?? Is it bad when the bypass valve kicks in at 5000+ rpm?

So should I try to get the Redline 20w50 synthetic or is there a better brand you would recommend? Mobil 1 seems to be quite popular in these forums.
I am thinking perhaps I should go back to Pensoil 20w50 for a few months and see if the oil
pressure goes back up.. At least I would have a baseline to work with...

Forgive me, I am a newbie to Porsche engine mechanics...
Old 02-07-2014, 01:47 PM
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I switched to Mobil 1 over 20 years ago after experiencing low oil pressure with valvoline Dino oil following some really spirited driving. Mobil 1 might not be the most expensive but it sure seems to work.
Old 02-07-2014, 08:08 PM
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I would never ever put Pennzoil in my car. Maybe the lawnmower.....
Old 02-07-2014, 08:15 PM
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I run Castrol in my lawnmower... Just kidding. That gets Mobil 1 also.
Old 02-07-2014, 08:37 PM
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Why change a good thing....I would never use a synthetic oil in my 930....NEVER...
Old 02-08-2014, 04:21 AM
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Penzoil: no good?!

@Tippy: I had Castrol GTX 20w50 before the Redline since I switch my mechanic (he retired
and moved) and I found oil pressure dropped - not significant but noticeable esp when idling at 800 rpm, sometimes DRUCK goes below 1. But at high revs the DRUCK does go to 5. With Penzoil
I always seem to get the proper oil pressure...

Is Penzoil not a good choice? My first mechanic swears by it.. I guess each mechanic has their own favourites. Someone else on another thread says to stay away from Brad Penn Oil as well...
Old 02-08-2014, 07:46 AM
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I would only use Pennzoil if I was low on oil and that was the only thing available. Feel the same about Castrol too.
Old 02-08-2014, 08:34 AM
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Quote:
Originally Posted by wgwollet View Post
Why change a good thing....I would never use a synthetic oil in my 930....NEVER...
Care to explain why?
Old 02-08-2014, 08:40 AM
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Quote:
Originally Posted by solarispete View Post
Hi guys, thanks for the responses! Much appreciated!

@Speedy Squirrel: thanks for your explanation. So does that mean that the 60 in 10w60 would be thick oil even when the engine is warm/hot? I am still not quite understanding that when hot the pressure would go down if the 60 oil is thicker than 50 oil... my limited understanding of oil pressure physics would be that I'd want a thicker oil so that it would keep higher pressure. Your explanation of the bypass valve: does it kick in when the engine thinks the oil is too thick so it tries to make the engine "flow" better?? Is it bad when the bypass valve kicks in at 5000+ rpm?

Yes, it does. The 60 means that it will be like a 60 weight oil at 100C oil temperature.
The heavier weight oil does raise the oil pressure.

You are correct, the bypass valve kicks in when the oil pressure is above about 5.4 bar. It is not considered good to have the pressure relief valve open at high RPM.

With a properly chosen oil, it should not be necessary either. I think 20W-50 is fine. When you switched to synthetic oil you also changed the weight, which may explain the differences in pressure that you observed. If you get a synthetic oil of the same weight as the Penzoil you were previously using (20W-50), the pressures will probably be the same (you have to be very careful to get the engine AND oil temperatures the same to make a good comparison).
Old 02-09-2014, 08:17 AM
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more clarification

@speedy_squirrel:

as per what you said,
"Yes, it does. The 60 means that it will be like a 60 weight oil at 100C oil temperature.
The heavier weight oil does raise the oil pressure. "

This is what I don't understand, assuming your logic above, I would expect 10w60 would be
higher oil pressure than 20w50. But instead, I am getting LOWER oil pressure when
car is warmed up (after 10 minutes of driving). And it's not a gradual oil pressure of
5 dropping to 4. I don't see 5 at all with 10w60 Redline Synthetic.

The oil sender/sensor was replaced when I first bought the car in 2010, so I don't suspect
it's faulty...

Thanks.
Old 02-10-2014, 08:38 AM
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Oil viscosity - 10/60 is always going to be thinner than 20/50, regardless of temperature, and thus, you will see less pressure on your oil pressure gauge. The multi-grade oils do not "thicken" with heat (I can't imagine that is what Speedy was trying to say, because it isn't so, and I know that he is an extremely knowledgeable guy) - all "thin" from their starting viscosity, but multi-grades with higher "2nd" numbers thin at a slower rate.
Old 02-10-2014, 09:11 AM
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