Hot (9:30) oil pressure low

[jhg41977]

I rebuilt the engine in my 96 993 to stock spec over the winter. I have about 3k miles on it now. At 1k miles I did a leak down, 1%-1.5% across the board. Oil pressure at operating Rev is 4.5 bar, at idle 2bar. Oil analysis has been great, slightly elevated silicone levels in the first two samples (20 min at 2k and 500 mile) 1k mile was good. 2k mile was good.

Break in oil was Brad Penn 30w breakin oil. After that BP 20-50. Filters both changed at each oil change (20 min, 500,1000 amd 2000)

I got caught in traffic the other day, 25 min or so, ambient temp 65/70, humid, on and off drizzle. Oil temp went to about 9:30. At idle, pressure dropped to 1-.5 bar. A tap of the throttle and it immediately went to 3-4.5 bar depending on rpm amd duration. After getting through traffic temp and pressure quickly returned to normal.

All oil lines were cleaned by pulling a wad of Terry cloth through using a steel cable. This was done a dozen or so times, rinsing the rag in mineral spirits each time, changing for final two passes, blown with air when done, next day two more passes with a clean rag, blow with air. Wait awhile, blow again and then hook it up. Oil cooler and tank were sent to Pacific Oil cooler for clean and check. Thermostat housing was cleaned at home.


Prior to rebuild, I don't remember the temp getting that high from such a short traffic stall. I never remember seeing pressure that low.

Thoughts?

[bpu699]

Oil cooler fan working? Thermostat working?

[jhg41977]

Uncertain. How can I trigger the cooler fan? Temp sensor and pressure sensors are new.

[otto_kretschmer]

Originally Posted by jhg41977

Thoughts?

you're fine, and I wouldn't worry about it

I use Smokey Yunick's rule of 10 psi for every 1000 rpm

half a bar is about 7 psi, so if your're idleing at 900 rpm and the oil pressure is in the 1/2 to 1 bar range I'd ignore it and just enjoy the ride


25 minutes of bumper to bumper will definitally heat soak an air cooled engine

if you often run into traffic like this, I would run a good synthetic oil

[Walt Fricke]

I'd have real numbers put on my oil temperature gauge. Lots of speedometer and instrument shops can do this. What is 9:30 in F or C? Isn't there a little mark in on the edge of the gauge inner face which indicates 100C? Somewhere in that area?

As Otto said, 1 bar at idle would have many of us laughing all the way to the bank, so to speak. That's just fine. Back when, Porsche used 10 bar gauges. At idle with those under warm conditions you thought you had no oil pressure at all. So they changed to the 5 bar gauge to get more needle movement per bar.

You ought to be able to run 12V directly to your cooler fan to see if it is working. If wondering if the sensor is working, and you can't get the oil temps up to where you can, when stopped, hear the fan, you could pull the sensor and measure resistance cold, and then when dumped in a pan of boiling water. Should show an open, and then just about zero resistance when hot.