Faulty oil pressure gauge diagnosis

Hi all,
New to the forum and this my first post, so please be gentle with me....
First on the list of many repairs needing carried out on my new 3500s is a faulty oil pressure gauge.
The gauge was temperamental when I first got the car, then for the past couple of weeks seemed to be working quite reliably - although somewhat low oil pressure was giving me some cause for alarm.
Now just yesterday its stopped working entirely, which is irritating because today I've put in some fresh 20w50 and I was hoping to see if this had any improvement on the oil pressure.
I've tested resistance on the sender, and with the engine still warm it was at around 2.5ohms. The sender appears to be new and shiny looking. The connector is nice and tight on it.
I've tried shorting the connector to earth, but gauge doesn't move. With the ignition on, but engine not started, the oil pressure light is on. Once started the light goes off. I've pulled the instrument panel out to check the gauge is connected up and it is, all the wiring back there looks fine.
So I'm suspecting the gauge may be at fault but thought I would see if there were any seasoned P6 veterans on here who might be able to tell me for sure before I go buying a new one.
Thanks guys!
 
I've tried shorting the connector to earth, but gauge doesn't move.

If that's the case and the fuel gauge is working meaning the voltage stabilizer is working then the gauge or the wiring is faulty. Check you have 10V at the gauge with the ignition on. Then ground the pin which otherwise is connected to the sender. Could be the wire is damaged in the bay. If you still have nothing the indeed the gauge is dead.
 
Thanks for the reply mate,
Well on my way back from work today the gauge mysteriously started working again, so I think I must have a wiring fault. If it stops raining at all today I'll have a probe with the multimeter and check the wire from the sender.
On the plus side changing the oil seems to have made a noticeable improvement on oil pressure, I'm now getting around 15 at idle when warmed up, so that's a relief!
 
Hi ,I,m new on here so not sure if this is where I comment, but after trying to obtain a new oil gauge sender [1973 v8] and failing to locate one that replaces the Smiths PT1812 [ OE No] exactly I prized the top off one of my dud ones ,cleaned the spring contact to the copper pickup under the lid and tested it with 40psi air presure and a 12v test lamp, hey presto working fine and now back on the engine .If you try this yourself then the least shock to undo the crimped joint the better and when re peening it the same applies, I used industrial silcon between the two which,now set means a dirt and waterproof seal.
 
Last edited:
Hi all,
New to the forum and this my first post, so please be gentle with me....
First on the list of many repairs needing carried out on my new 3500s is a faulty oil pressure gauge.
The gauge was temperamental when I first got the car, then for the past couple of weeks seemed to be working quite reliably - although somewhat low oil pressure was giving me some cause for alarm.
Now just yesterday its stopped working entirely, which is irritating because today I've put in some fresh 20w50 and I was hoping to see if this had any improvement on the oil pressure.
I've tested resistance on the sender, and with the engine still warm it was at around 2.5ohms. The sender appears to be new and shiny looking. The connector is nice and tight on it.
I've tried shorting the connector to earth, but gauge doesn't move. With the ignition on, but engine not started, the oil pressure light is on. Once started the light goes off. I've pulled the instrument panel out to check the gauge is connected up and it is, all the wiring back there looks fine.
So I'm suspecting the gauge may be at fault but thought I would see if there were any seasoned P6 veterans on here who might be able to tell me for sure before I go buying a new one.
Thanks guys!
Hi, I expect you have already made sure the feed [12v+] contact on the gauge is live ,fed from the printed circuit,if so and you earth the other contact it should,as I,m sure you know, go all the way up.It sounds as though it may well be the gauge but this simple test will confirm,cheers Richard.
 
Thanks Richard, I'll be sure to try that the next time it stops working, as the gauge is now working again and has been for a couple of days (with no help from me I might add, it just pinged back on one morning). Surely must be a wiring fault
Whilst we're on the subject, what's likely to cause the needle to move very lazily up and down? If I'm cruising along at 60mph the needle will sit around 30, after stopping and idling it takes about 10 seconds to drop down to around 15, then the same when driving again. It just sort of floats around on there, is that likely to be the sender?
 
The instruments are driven by a hot wire on a bimetallic strip which takes a time to cool or heat and thus moves slowly . Its basically damped so the fuel gauge for instance is not bouncing around when cornering etc.
 
Ah okay, I thought it would move a bit faster with the revs. I seem to remember the pressure gauge on my old Scimitar moving up and down quite quickly when you revved it, but I seem to remember a lot of things sometimes
 
Back
Top