Oil Pressure Gauge Maxed

markagsmith5 · #1

I noticed yesterday that my oil pressure gauge was maxed out with the engine running.
I did a test and here is the timeline
0 sec - ignition on - oil light on, pressure gauge 0
1 sec - cranking engine - light off, gauge max
2 sec - engine running - light off, gauge max
7 sec - engine off - light off, gauge max
7 sec - ignition on - light off, gauge max
17 sec - light on, gauge max
19 sec - light on, gauge 0

My suspicion is the pressure sender. Appreciate any thoughts.

walfreyydo · #2

Swap the wires on the sender or check the wiring/connections. Usually when the gauge faults reading high, its an issue with the sender or the wiring/connections.

I just had this issue and discovered one of the wires was loose on mine. Reconnected and it started working properly again. I would not immediately replace the sender until youve eliminated wiring/connections as the culprit.

This area is also directly under the oil filter and often gets caked in oil and grime due to the inevitable oil spillage that always seems to happen on these cars and the horrible placement of the filter. That grime could also be causing an issue with getting a good connection on the sender connections.

dr bob · #3

What he said, plus a warning. Brass screw terminals on the VDO senders are extremely fragile. Voice of experience speaking... 'Servicing' the connections means carefully loosening, then cleaning, then carefully restoring the nuts on those studs. The definitive torque spec is "barely snug", no more than it takes to keep the wire from falling off. I let the lockwasher do the hard work here, and add just enough torque to start compressing them so they can do their jobs. Finger-tight with a nut driver, never a wrench. Don't put a driver on the nuts to 'snug them up' without loosening them first, or the first available movement will risk breaking the brass stud.

Have you done any work near that sender recently? Something that might have disturbed the connections and wires there recently? Original wiring has become stiff and even crispy with age and heat exposure. If you've used petro-based engine cleaners, or (gasp!) Brake Clean for casual degreasing, those leach the oil parts of the PVC wire insulation, causing the wire to age even faster. Anyway, stiff wires make it easy to disturb a sender connection just by bumping the wires even away from the sender a bit.

On my car, the stuck-up cousin to yours, those sender connections pass through an easy to access engine harness connector high in the engine bay. You can easily verify the integrity of the wiring and connections with a DMM from there. The sender on the 928 has two connections on it, so pretty easy to verify both from that engine harness connector with a meter. Guessing your car has a similar accessible connector.

The Good News is that the senders are pretty easily available. Get a genuine Bosch/VDO if you need to replace. Some of the aftermarket replacements have proven sketchy in both accuracy and lifespan.

Tom · #4

Watching that video, it looks more like the sender (or maybe the cluster) to me. Odds would say it's the sender, but there is a curious quirk I can't account for with confidence. As soon as the motor starts to build oil pressure, the gauge pegs. After the motor is off, as the pressure drops, the gauge stays pegged until there is virtually no pressure left (as indicated by the warning light coming on just before the gauge drops to zero). All that would point me toward the sender. The quirk is that the gauge is remaining pegged even as you cycle off the key. Notice how the volt and boost gauge drop to zero before turning the key back on. That's normal. What's not normal, is for the oil pressure gauge to remain pegged while the key is off like that. It should drop to zero with the key off, then jump up to whatever the pressure is at the moment you turn on the key, then fall to zero over time as the pressure drops to zero. Where is the gauge getting power to stay pegged? Is some capacitor remaining momentarily charged? Or is the cluster or gauge defective?

The good news is, no guessing needed. Easy to check. Remove the blue/white wire from the G terminal. That wire feeds to oil pressure gauge needle. The sender generates an increasing amount of resistance to ground as the oil pressure goes up (1, 2, 3, 4, and 5 Bar of oil pressure equals 29.6, 65.3, 98.9, 133.6, and 184.0 ohms to ground, respectively.) As a simple check of the gauge, connect the blue/white wire to a 100ohm resistor and ground the other side of the resistor. With the ignition on, that should give you about 3Bar on the gauge. If the gauge pegs to 5+ instead, then investigate the wiring to the cluster and the cluster/gauge itself. If the gauge reads about 3 with the resistor hooked up, then you've all but confirmed the sender is bad. If you want to confirm that, you can put a multimeter on the G terminal and check its resistance to ground when you start the motor. Chances are good you will see an open circuit or thousands of ohms.

That's not to say it couldn't be just a bad connection. That's possible too, but a little testing should tell the tale....

I keep an assortment of resistors handy for these types of things. 2W resistors seem safest here since I don't know the impedance of the gauge, but do know the circuit will have at least 100 ohms.

https://www.amazon.com/ALLECIN-2W-Metal ... 9hdGY&th=1

p.s., I edited the original post to remove the tags around the youtube link. URL tags prevent videos from embedding -- just post the youtube link as is and it will embed and play here on Carpokes.

icb · #5

I'd say the gauge staying pegged like that after power is removed is mechanical - the needle is sticking from being slammed up into the stop. See if it will drop down by gently thumping the dash above the cluster.

Tom · #6

icb wrote: Sat Jun 14, 2025 11:56 am I'd say the gauge staying pegged like that after power is removed is mechanical - the needle is sticking from being slammed up into the stop. See if it will drop down by gently thumping the dash above the cluster.

Good call. Definitely possible, although it drops to zero shortly after the warning light goes on. Would be interesting to know how long it says pegged if he just turned off the key and waited and/or if tapping on the cluster frees it up.

markagsmith5 · #7

Today I tested as per https://www.clarks-garage.com/shop-manu ... 19.htm#oil
I used a 1k Ohm variable potentiometer in parallel with a 220 Ohm resistor which gave readings on my DMM of 14.2 - 195.4 Ohms. The oil pressure gauge responded appropriately ie from 0 to a tad over 5.

markagsmith5 · #8

Tom wrote: Sat Jun 14, 2025 1:40 pm
icb wrote: Sat Jun 14, 2025 11:56 am I'd say the gauge staying pegged like that after power is removed is mechanical - the needle is sticking from being slammed up into the stop. See if it will drop down by gently thumping the dash above the cluster.
Good call. Definitely possible, although it drops to zero shortly after the warning light goes on. Would be interesting to know how long it says pegged if he just turned off the key and waited and/or if tapping on the cluster frees it up.

Tapping the cluster did make the gauge drop to 0.

Tom · #9

markagsmith5 wrote: Sun Jun 15, 2025 11:36 pm Today I tested as per https://www.clarks-garage.com/shop-manu ... 19.htm#oil
I used a 1k Ohm variable potentiometer in parallel with a 220 Ohm resistor which gave readings on my DMM of 14.2 - 195.4 Ohms. The oil pressure gauge responded appropriately ie from 0 to a tad over 5.

You could put a multimeter on the oil pressure sender to confirm 100% that it's the culprit, but based on that test and your symptoms, the sender is almost certainly bad...

markagsmith5 · #10

Put a multimeter on the G connection on the sender. It read around 10 Ohm with the engine and ignition off, then jumped to infinite resistance as soon as the engine started. Have ordered a new sender.
Thanks all for your help and advice.