Rockit

I've owned this car just over a year. I've noticed 2 different oil pressures with different oil weights that I would have thought I would get just the opposite outcomes. I'm not sure what to think of it.

I was running 0-40w sine I got the car. My oil pressure was always pined at 5 and never moved, cold or hot days idle or not. The oil temp always ran around the first line.

I recently switched to 10-60w, the engine is quieter but yesterday was first hot day. This is the first time the oil pressure dropped at idle to 2. The oil temp did for the first time go just above the first line to almost half. I was in slow stop and go driving...both the temp and oil pressure have never done that with 0-40 in hot weather.

There is nothing wrong with the car, once I stated to mover and drive it was normal...

I know about cars...I would think the thicker oil would run cooler and the oil pressure would be higher...I don't know what to make of this.

LexVan

Should not be running 0W40 in a 993 unless you live in the Arctic. Run a quality 15w50 or 20W50 instead.

vincer77

Still seems odd that you have less oil pressure than with 10w40. Sure you remember correctly.

Your current oil pressure behavior seems normal.

Drisump

As was said by Lex, no air cooled Porsche (even in the arctic) should be running 0 weight oil. Sounds like you have a problem with your pressure gauge because it should always display a different number depending on RPM....also, you should never be "pinned" at 5 bar. Cheers

Rockit

You guyz are no help so far

TMc993

Try this:

Oil pressure:

Oil pressure goes up and down with engine speed. So, readings on your oil pressure gauge should go up and down with engine speed.

Your statement that the oil pressure was "pined (sic) at 5" leads one to suspect that either your oil pressure sender or gauge or both were not functioning properly when you were using the 0-40 oil.

Your statement that with the 10-60 oil, the oil pressure gauge goes down to approximately 2 at idle and then is "normal" (I guess you mean close to 5) at driving speeds indicates that the oil pressure sender and gauge are now working properly.

Oil temperature:

In a 993, from cold start a properly functioning oil temperature gauge indicates rising oil temperature until the gauge hits approximately 9:00 o'clock, at which point the oil tank thermostat opens, sending cooler oil into the engine and causing the gauge to drop back between 7:00 and 8:00 o'clock. Depending on a number of factors that occur while driving, the oil temp may rise and fall, which should be indicated on the oil temp gauge. In warm weather it may rise closer to 9:00+ and in cold weather drop lower than 7:00.

The fact that your oil temperature "always ran around the first line" would indicate to me that your oil temp sensor/gauge circuit was also malfunctioning with the 0-40 oil.

What you are seeing now (Oil pressure rising and falling with RPM and oil temp rising to 9:00 before falling) is indicative that your oil pressure and oil temp circuits are now working properly.

So, it appears that those circuits didn't work properly at one time, but are now working as they should.

That's what I make of it....

OverBoosted28

I'm just curious of any lasting/permanent damage, from running the wrong (0w40) in the aircooled engine.....

Rockit

They may have caused a hole in my piston. I still don't know what snapped the crack shaft.

Raleigh993

Good explanation Terry.

Churchill

40 weight oil won't do damage so long as you're not running it for years on end. You want 50 weight oil, but a few thousand miles of 40 isn't going to hurt anything. It's just not ideal.

This sounds like a sensor or instrument problem, because it's simply not possible that your pressure was always 5 bar in reality. I wouldn't worry about it so long as you're getting normal readings with 50 weight oil.

cgfen

LOL
Instigator!

Steve Weiner-Rennsport Systems

Yes.

Accelerated wear on crankshaft thrust bearings and IS bearings for a start and those items are not inexpensive to replace.

Rockit

Thanks so much for taking the time to write this excellent explanation.

I'm not new to cars or bikes and I'm a very good mechanic. I'm just new the 911's and any quirks they might have.

My temp sensors and oil pressure gauge and switch are working perfectly and always have been, you can take that out of the equation.

That's why I posted this because the thinner weight held MUCH better oil pressure and that is usably not the case. With 0-40 I did get lifter noise while it was cold for a while. The oil temp always ran normal and even at idle the pressure read 5. The oil pressure did move slight and that's how I knew it was working.

Thought maybe someone else here may have noticed the same thing...guess not.

SwayBar

It's a little too convenient that both gauges malfunctioned at the same time. My take is this:

The lower viscosity oil will flow a greater volume of oil, and will do-so at a lower oil-friction point than the heavier weight oil. In other words, the oil itself is generating less heat due to shear.

Additionally, because of the higher volume of oil circulating thru the engine, the engine will run cooler as that higher volume of oil will wick-away more heat and expell it thru the cooler(s) per unit of time regardless of RPM, versus the heavier weight oil.

The only question is whether the oil pump can 'keep up' and maintain sufficient flow/pressure at higher RPMs. According to your observations, it looks like yes.

Rockit

Thanks...

With 0-40 it was always at 5bar hot as hell or cold at idle. Again oil temp was always at the 1/4 line, only draw back was lifter noise until the engine fully warmed up. When I had the car restored the shop said that was the right weight oil to use.

when Porsche came out with 10-60w now for the 993 air cooled I switched. That's when the oil pressure dropped to 1 to 2 bar at idle and in stop and go the oil temp reached almost half in the oil temp, still all safe but it did freak me out driving the car for almost a year and that never happing.

I've been working on cars and bikes for 40 years..I've never seen this or would have expected these kinds of results from heaver oil. Its a fact on my racing Triumph heavier oil raises the oil pressure at any rpm.

1 bar=14 psi
2 bar=29 psi
3 bar=43 psi
4 bar=58 psi
5 bar=72.5 psi