question about oil gauge

Eldorado · 11-01-2006, 02:39 PM

inspired to ask by this current thread, I've got a question about the oil gauge.

When i first start the car, it'll hover around 4bar... then as the car warms, down to about 2.5 bar... the warmer it gets, the lower the reading. after driving for a good 40 mins to an hour, It'll get to a point where at rest it'll read 1.25 bar, and maybe 1.5 - 1.75 bar while at highway speeds.

This obviously isn't right. It's been like this in the near 2 years that I've owned the car... it was like this for the 2 years the PO owned the car... and I even talked to the guy who owned the car before HIM, who owned it for i think 6 years... middle aged doctor near town here and he said it was always like that...

so we've got these readings which have been constant for coming up 10 years now..

what do you think? Oil pressure sender? bad gauge? me being paranoid?

this thing loses maybe half a quart of oil every 7000 or so KM... and oil always looks great when draining (as great as old used synthetic oil can look at least)... No temp problems... no power/driving problems......

what do you think?

rb101 · 11-01-2006, 03:19 PM

My oil pressure is 4.5-5 bar cold on start up idle, after its warmed well it can drop to 1-2 at idle. It is 5 bar anywhere past 2K rpm when fully warm. Well at least that's what mine does at 160K miles. I vote your pressure sender or gauge is going bad. You can always pop in a mechanical guage and verify your gauges and sender.

Rick

pozican · 11-01-2006, 03:39 PM

When my NA is warm it runs at idle at 3, and at 1.7k rpm or so it'll hold steady at 4....

In the turbo?
It's off the charts...

Slam · 11-01-2006, 04:06 PM

OPRV valve spring tired?

Mine hits 5 bar at cold startup and I get about 1 bar for every 1000 RPM while driving when the car's warmed up, and about 1.5 bar at idle warm. I'd worry if the gauge is reading 1 bar at warm idle and bouncing. You could plumb in a gauge and verify. The oil pressure gauges on these cars don't fail very often.

1.75 bar at highway speeds seems low. The 1 bar per 1000 RPM rule is a good yardstick. You should have around 3 bar at highway cruising speed (11o km/h) to be safe. Some guys figure much higher than that. What weight oil are you running?

Eldorado · 11-01-2006, 04:11 PM

10w30 synthetic..

maybe i'm off with my 1.75bar... I'll try your 1 bar per 1000rpm next time i'm out in the car.

how would i add in a new gauge to test the one in the dash?
how would i test the sender?

Slam · 11-01-2006, 04:29 PM

IIRC there's a point on the OPRV/cooler housing to plumb in a gauge. Bolt in threaded hole upstream of sending unit. I run 10/30 as well. Don't know how you would test the sender - I suppose by comparing the plumbed-in gauge to the dash one.

I haven't really made up my own mind about the oil pressure in my car yet. Our 924 turbo showed 1.5 bar at idle but the gauge bounced, then it bounced while coming off idle. Within two weeks the rod bearings had gone. I'm still kicking myself for not trusting the gauge and looking for an electrical problem instead.

My 944 reads a little low for my liking but the needle doesn't bounce the way the 931's did. When it does, I'm opening it up right away. In fact, I've got the bearings and oil pan gasket standing by. Just a little nervous about the job...

Razorback1980 · Razorback1980's Garage

With the oil being thicker at startup, one would expect the pressure to be higher. I think there is a specification in the manual on what the pressure should read but I can't remember what it was...I'll try and look that up.

Eldorado · 11-01-2006, 05:48 PM

wouldn't you know it... I should have RTFM :P
I forgot i had it saved on my computer...

"Engine oil pressure is shown in bars.
At 5.000 rpm, with the engine at normal operating temperature (approx. 90°C / 194°F), the pressure should be approx. 4 bar. A slight drop in oil pressure is normal under certain operating conditions such as prolonged highway driving in hot weather.
At idle speed, with the engine oil hot, the oil pressure can sink to 0.5 bar - this does not indicate any loss of engine performance.
However, if the oil pressure drops suddenly while you are driving, or if the warning light comes on, pull off the road, stop the engine and wait for it to cool down. Check the engine oil level. If the oil level is normal, contact the nearest dealer."

I love how it says "if the oil level is normal, contact the nearest dealer.."

I'd love to hear what the technical writers wanted to write for "If the oil level is NOT normal, ........"

Slam · 11-01-2006, 06:16 PM

Hehe...

You know, while I was playing with my oil cooler, I installed the 3-piece OPRV from the wreck's engine. It was an update on mine - mine is just a slug, basically. The wreck's valve was flanged slug. Both were bored out to take the spring, and the spring designs were slightly different. When I used the wreck's OPRV and spring, I had low oil pressure, and the warning light was on at idle. So I switched back and the pressure came back to where it was. Interesting how Porsche changed the design over time. My car didn't like the update...

Eldorado · 11-01-2006, 06:54 PM

actually simon, the manual also mentions that.. it says that it's normal for the light to come on at idle.. as long as it goes away when you accelerate.