If it jumps to 2bar when you move the key to II before you start the engine the sender is going bad, if it just twitches a bit it's OK. Most will twitch a bit when they first get power but it should still stay in the red down very close to 0.

It should stay at 0 'till the engine is running and then raise in a smooth motion to a final reading which will depend on lots of factors including oil weight, engine condition and others, this is usually ~2.5-4 bar at idle based on the 4 240s I've owned and 5-6 gauge installs I did for friends. There will certainly be cars that run higher/lower out there however.

It then will (usually) go up a bit with rpm, I did have one car that stayed steady at 4 bar from idle to redline with only a bit of motion but it still came up smoothly from 0 when started.

I did have one sender that tested good with an OHM meter and when installed it had issues, it stayed at 0 'till the engine started but when it got oil pressure at idle it pegged hard and fast. The same symptom will occur if the wire going to the sender from the gauge is on the "WG" terminal instead of the "G" terminal. The "WG" terminal is for the idiot light and opens at ~7psi causing the gauge to peg.

Lots of ways for these to fail, hard to diagnose without seeing the situation first hand. Hope there is enough information here for you to tell.

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Dave Shannon
Durango, CO
'63 P-210
'67 1800s
'88-240
'01 Wrangler
'06 F250 Diesel 4X4
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