Oil Pressure Warning Light

[rennch]

Hi,

I've searched a bit, but haven't seen anything exactly like my issue here.

My oil warning light "faded" on yesterday, and I can't figure out why yet. All guages look right (Oil pressure, temp, level), I've just replaced the switch, and it still does it.

I start the car, then after about 15 seconds the oil warning light sloooooooooowly fades on then stays solid. My buddy thinks it's a short somewhere, but I'm not so sure. What else should I be looking for?

Thanks,

mike

[rennch]

nothing, huh?

[Kroggers]

Does it only come on at idle, and go off when you are driving? If so, then this is a known Porsche feature on the older cars. I had the same happen to me, and fixed it with the 'oil line restrictor' upgrade - http://www.dietersmotorsports.com/tech/2002/3-2002.htm

[SteveP]

Hey Mike,

What sort of oil pressure is showing on your gauge when the warning light comes on?

I'm running around 4-5 on the pressure (druck) gauge in my pcar ('86 3.2 Carrera) 15 seconds after starting from cold.

Steve

[rennch]

No...it comes on, and stays on, unfortunately. It's at about 20 at idle, then boosts up with the throttle pretty normally.

[SteveP]

Is this problem occurring when you start the engine from stone cold (ie. first start of the day), or when the engine is warm, as 20psi at idle on a cold start (when the engine oil has less viscosity - ie. is 'thicker') seems awful low to me

[rennch]

Well, I do have a couple of big oil leaks I have to track down. I am not sure if that has anything to do with it.

[rennch]

My plan today is to make a jumper from the oil pressure switch to the gauge and see if it's faulty wiring (which I hope and suspect) vs. an actual pressure issue. Keep you posted.

[2.7RACER]

Your oil light, of course, shouldn't come on with 20 psi at idle. The normal leaks have nothing to do with your pressure or the light, unless all the oil leaks out. Something, I'm confident, would get your attention.
Here's a simple test: Remove the connector from the oil pressure switch, then start the engine. The light should remain off. If it comes on, your buddy is correct, there is a problem with the wire.
The oil pressure switch is a switch, either on or off.
Check the switch with the motor off with an ohm-meter to ground. Should be no continuity. Nothing.
Now start the motor with the meter leads connected to the switch and the connector off. The meter should read continuity, close to zero ohms to ground.
If the meter reads some resistance that isn't close to zero the switch is bad.
It should only read on or off, nothing in between.
It is possible oil is leaking into the switch causing your problem.

[DW SD]

Originally posted by 2.7RACER

Here's a simple test: Remove the connector from the oil pressure switch, then start the engine. The light should remain off. If it comes on, your buddy is correct, there is a problem with the wire.
The oil pressure switch is a switch, either on or off.
Check the switch with the motor off with an ohm-meter to ground. Should be no continuity. Nothing.
Now start the motor with the meter leads connected to the switch and the connector off. The meter should read continuity, close to zero ohms to ground.
If the meter reads some resistance that isn't close to zero the switch is bad.
It should only read on or off, nothing in between.
It is possible oil is leaking into the switch causing your problem.

Doug's got a good method for testing, but I think his suggestion is opposite. The idiot light lights when there is continuity through the pressure switch. IE 0 ohms resistance (at low pressure). Conversely, above some threshold pressure, there is no continuity (infinite resistance) and the idiot light goes out.

So look for zero ohms when the engine is off and no continuity when it is running.

I just tested my low oil pressure sender the other day and hooked up a regulator while measuring continuity. It has zero ohms below 11 or 12 psi.

[2.7RACER]

DW SD,
Thanks for the catch. You are right. Continuity when the motor is off, open when running. I need a copy reader.

[IXLOR8]

Is the oil light bright on start up for several seconds, and dim while running?

[rennch]

ok...update. I pulled the wire from the switch, and had the same results. Car starts, then the warning light goes from dim to bright while it's running. I'm hoping (and assuming) that it means I *don't* have an oil pressure problem, and it's definitely a wiring issue. So, that means I have to start tracing the wire back to see what's going on, I suppose. Right?

[DW SD]

It is a wiring issue. This doesn't confirm you don't have a pressure problem, but it is a VERY good sign

I would believe that your wire to the low pressure switch is grounded between the idiot light and the back of the car. Look for the wire harness to be cut or pinched somewhere.

I think the low oil pressure sender simply grounds itself out when the pressure drops, which completes the circuit and lights the light.

SO......If your circuit finds another path to ground, the light will light, independent of the switch.

Doug

[rennch]

Doug et al, Thanks for the tips. I'll get under the car now and try to figure her out..

Thanks!

[rennch]

Ok...update again. I've done a few more troubleshooting things. I made a long "patch" wire and ran it from the pressure sender directly to the gauge, with the same results. This leads me to believe that it's not oil pressure related at ALL, but has something to do with a short in the e-brake light, which shares the same warning light in the 69. Since happened with and without that being connected, it points me in that direction. What say yous?

[rennch]

Man this is frustrating!

So...if I just turn the key on, without starting the engine, I get the same exact light. It fades on, then stays solid.

Based on the other stats, it still seems like an electrical issue to me. Maybe with the eBrake?

[DW SD]

Can you disconnect the wire from the ebrake light attached at the gauge?

OR is it tied in at some other point?
It is surprising that the light is shared with the oil pressure?
Weird!

Doug

[rennch]

Doug,

I haven't tried that yet. I had had enough today, so I put it away, frustrated. It just dawned on me that you've got that sweet RSR I was checking out last Oct. in SD. I was in town for the Steelers/Chargers game, and when I went to Qualcomm, there was a PCA event going on. I wish I had known, I would have tried for a co-drive. Nice car though!

[ruf-porsche]

Are you sure its the oil pressure light and not the alternator light?