Oil pressure warning light

[Chris A]

I started the car and oil light came on nice and bright then went off as it should. When I was a little way up the road I noticed it was flickering intermittently very faintly, hardly visible. Returned home carefully.

I would have expected that if there was a loss of pressure the light would be full brightness, ok so maybe not. I disconnected the wire at the sender end on the engine - the light still flickers and does seem to be engine speed sensitive. At tick over I can't see it but rev it a bit and it is just visible.

My logic was that there is a short somewhere, so quick inspection under the dashboard nothing immediately obvious. Next I put a piece of cloth around the end and the wire that connects to the sender. Same thing.

I suppose that my next step would be to rig up a cable to go direct from the sender to the bulb holder to see if this clears the problem.

Am I on the right track, or do you know something I've missed or my logic is wrong.

Worried of Normandy🙄

Time for my mug of tea

Thanks 

[NonMember]

While there are some electrical possibilities for this behaviour, most are very unlikely. It could, just about, be some capacitive or inductive coupling from a wire with high frequency high currents or voltage. The feed to the coil is just about the only option there. More likely is a partial short, where the loom has been rubbing on something. If the insulation has worn through, the oil light wire might be rattling and making very momentary contact with the bodywork.

Also worth considering whether the illumination you're seeing is actually from the oil light bulb. The inside of the instrument is not as well sealed as it could be.

[johny]

yes dont think this is an oil problem but obviously needs to be corrected before driving anywhere. As Rob says most likely a weak earth fault in the wire from the bulb to the pressure switch. If you disconnect it at the switch you should be able to measure system voltage to earth on the connector anything less means its shorting to earth somewhere...

[Chris A]

4 minutes ago, NonMember said:

Also worth considering whether the illumination you're seeing is actually from the oil light bulb. The inside of the instrument is not as well sealed as it could be.

Definitely from the bulb as it is visible with the car parked, bonnet up or down.

 

6 minutes ago, NonMember said:

More likely is a partial short, where the loom has been rubbing on something. If the insulation has worn through, the oil light wire might be rattling and making very momentary contact with the bodywork.

That's my favoured option, well rather that than failing oil pump 😱 Looks like a complete check of the wire from stabiliser to bulb, bulb holder to sensor and a dislocated back caused by having to look under the dash.

10 minutes ago, NonMember said:

It could, just about, be some capacitive or inductive coupling from a wire with high frequency high currents or voltage

Interesting, I have an electronic voltage stabiliser fitted very close to it, could this be causing some interference?

[Chris A]

4 minutes ago, johny said:

yes dont think this is an oil problem but obviously needs to be corrected before driving anywhere. As Rob says most likely a weak earth fault in the wire from the bulb to the pressure switch

I could just give the car a really good high speed thrash around the lanes - if the engine blows up then oil pressure problem, if not faulty earth. On second thoughts maybe not a good idea as you say. Yes sort it before it leaves the premises again!

[johny]

well as long as it comes on full brightness with engine stopped youre pretty safe. The worst thing is if it comes on full brightness when out driving because the earth fault has worsened you wont know where you are😰 

[Badwolf]

I had this problem a couple of years ago. It was suggested here that it could be the oil pressure release valve. Replaced it, no more problems. The hive mind will without doubt explain why.

[Chris A]

1 minute ago, Badwolf said:

It was suggested here that it could be the oil pressure release valve. Replaced it, no more problems.

OK, another possibility to look at after the wiring.

[Chris A]

6 minutes ago, Badwolf said:

I had this problem a couple of years ago. It was suggested here that it could be the oil pressure release valve. Replaced it, no more problems. The hive mind will without doubt explain why.

Just looked at the parts diagram. Did you replace the whole assembly or just the spring?

[Badwolf]

I have checked the responses on my restoration thread. The thought was that a small piece of swarf which I found when I took the PRV apart might have been holding the valve open and so causing lower than normal oil pressure. Worth whipping yours out for a look and a wipe over. Have a look here, part way down the pages...

https://forum.tssc.org.uk/topic/2623-back-to-the-plot-at-last-nose-to-tail-1972-spitfire-mkiv-restoration-upgrades/page/8/

And

https://forum.tssc.org.uk/topic/2623-back-to-the-plot-at-last-nose-to-tail-1972-spitfire-mkiv-restoration-upgrades/page/9/

[Badwolf]

7 minutes ago, Chris A said:

Just looked at the parts diagram. Did you replace the whole assembly or just the spring?

Chris - Previous  post should assist. Just the spring, piston and seal. Dead easy job, even for me. Guidance courtesy of Angelfire.

I think that I might have also fitted a new oil pressure sensor as well.

[johny]

But in this case its happening with the pressure switch disconnected so I know our cars are sneaky but if its an oil problem it really will be one for the books😁

[Chris A]

15 minutes ago, Badwolf said:

Chris - Previous  post should assist. Just the spring, piston and seal. Dead easy job, even for me. Guidance courtesy of Angelfire.

Just had a look at those posts, thanks. Oil would be due for a change this summer so I guess having to empty it isn't a waste. Tricky part is a drill bit 9/16", unless the closest metric will do 😁

 

2 minutes ago, johny said:

But in this case its happening with the pressure switch disconnected so I know our cars are sneaky but if its an oil problem it really will be one for the books😁

Exactly, I still think the most likely suspect is a fault in the wiring somewhere letting it earth.

I should be able to have a closer inspection in the next couple of days

[Badwolf]

I vaguely remember, when I removed the PRV very little oil came out.

[NonMember]

2 hours ago, Chris A said:

Interesting, I have an electronic voltage stabiliser fitted very close to it, could this be causing some interference?

No, there's not enough high current at high frequency for that. I actually can't think of anything that really fits the bill for the obscure inductive/capacitive coupling explanation. Look for damage to the loom. Sorry, in advance, about your back.

[Pete Lewis]

i would make sure you dont have the generator and oil warning bulbs in the wrong holders

short the LP wire to earth  ... which bulb illuminates 

if the wire to the LP switch is off the switch  its nothing to do with the engine lubrication

Pete

[Chris A]

57 minutes ago, Pete Lewis said:

i would make sure you dont have the generator and oil warning bulbs in the wrong holders

short the LP wire to earth  ... which bulb illuminates 

if the wire to the LP switch is off the switch  its nothing to do with the engine lubrication

Pete

No mix up with bulbs, they haven't been touched in ages.

I'm convinced it is nothing to do with the engine lubrication, my wallet gave a big sigh of relief!

[cliff.b]

"Looks like a complete check of the wire from stabiliser to bulb, bulb holder to sensor"

I don't think the supply voltage comes from the voltage stabilizer, believe it's 12v directly off the ignition switch to the bulb. If it were me, I would temporarily put a new piece of wire from the sensor to the bulb which should prove if the original is shorting or not. 

Or if you have a meter, disconnect that wire at both ends and check for any resistance to ground. There shouldn't be any.

[Chris A]

9 minutes ago, cliff.b said:

I don't think the supply voltage comes from the voltage stabilizer, believe it's 12v directly off the ignition switch to the bulb

Effectively that, the  diagram shows it on the input side of the stabiliser so yes 12v from ignition.

15 minutes ago, cliff.b said:

it were me, I would temporarily put a new piece of wire from the sensor to the bulb which should prove if the original is shorting or not. 

That's the same conclusion I have come to. I need to look at how I can link it in easily. The wire is soldered direct to the bulb holder which means I'll have to cut it and fit connectors. Although I have test cables I don't think I have a length of suitable cable in stock for a permanent replacement, visit to motor factor called for this week.

[cliff.b]

4 minutes ago, Chris A said:

Effectively that, the  diagram shows it on the input side of the stabiliser so yes 12v from ignition.

That's the same conclusion I have come to. I need to look at how I can link it in easily. The wire is soldered direct to the bulb holder which means I'll have to cut it and fit connectors. Although I have test cables I don't think I have a length of suitable cable in stock for a permanent replacement, visit to motor factor called for this week.

You could always wire a completely new circuit in temporarily. Take a new wire from any convenient 12v point, connect to any spare low wattage bulb & then to pressure switch. Hang bulb anywhere you can see it and go for a drive 👍

[Chris A]

53 minutes ago, cliff.b said:

You could always wire a completely new circuit in temporarily. Take a new wire from any convenient 12v point, connect to any spare low wattage bulb & then to pressure switch. Hang bulb anywhere you can see it and go for a drive 👍

Yes, but although I have spare bulbs no bulb holders 😒

[cliff.b]

21 minutes ago, Chris A said:

Yes, but although I have spare bulbs no bulb holders 😒

Soldering iron 🙂

[Peter Truman]

6 hours ago, Badwolf said:

have checked the responses on my restoration thread. The thought was that a small piece of swarf which I found when I took the PRV apart might have been holding the valve open

Early 70's at 5AM enroute from Stokesley to Teesside Airport for wife to fly to Belgrade my Mk2 Vitesse oil pressure dropped from its normal 70psi+ to 40psi I reasoned it still had oil so pushed on. Dropped wife off, checked there were no oil leaks so reasoned it must be the pressure relief valve so dismantled it, all looked OK, no damage, put a rag down to clean seat no debris put it all back together & fired her up and normal 70+ oil pressure and in 50 years never had a repeat & the engine has never been out, rebuilt, or had an issue. So what caused the valve to hold open I'll never know! I have subsequently checked the length of the spring and its within tolerences, I even fitted a slightly longer NOS one, but same 70+ oil pressure so reverted back to the original.

[Chris A]

9 hours ago, cliff.b said:

Soldering iron 🙂

Got one! Somewhere in the bottom of my 'tools I never use' box. Solder? I think there might be a bit there as well.

My first check will be to follow the route of the wire ( especially behind the dashboard in the mess there!) and loom to look for any obvious damage causing the short circuit. If the loom/wire is rubbing on something it could cause more trouble in the future so better  to be safe than sorry. Second step, make a completely new length of wire from the bulb holder to pressure sensor as I'm convinced it is along this section that there is a problem.

 

[cliff.b]

6 minutes ago, Chris A said:

Got one! Somewhere in the bottom of my 'tools I never use' box. Solder? I think there might be a bit there as well.

My first check will be to follow the route of the wire ( especially behind the dashboard in the mess there!) and loom to look for any obvious damage causing the short circuit. If the loom/wire is rubbing on something it could cause more trouble in the future so better  to be safe than sorry. Second step, make a completely new length of wire from the bulb holder to pressure sensor as I'm convinced it is along this section that there is a problem.

 

Sounds like a plan 👍