Oil Pressure Gauge Gremlins

Took the LM out today - all seemed fine and I even commented to my son that the temperature and oil pressure were indicating OK (if that means anything given the 'known' inaccuracy of these gauges!), then after a spell stuck in heavy traffic and roadworks (Lincoln - hopeless on a weekday!), I noticed that the oil pressure gauge needle had dropped to the top of the left hand orange bar. It has never done this before, so I was a little concerned but just had to keep going as I was caught in the traffic.

Anyway, although the temperature crept up little in the queues, the fans kicked in and kept it OK, and everything seemed to be fine. Once on the clear road to home the gauge still did not register but the car behaved normally. There's nothing to see - no leaks, no unusual noises either, and the oil pressure warning light has not shown once. Any ideas on where I should start? Could this be the pump relief valve stuck open - and how do I check that? The oil is pretty clean; changed only a short while ago together with a new filter and relatively few miles travelled since.

When I switch the ignition on, the oil pressure gauge 'activates', in that the needle rises to the right hand side of the orange line, but it doesn't even flicker when the engine is started. I would welcome a few pointers or ideas from anyone who has experienced the same issue - many thanks.

Paul T

How far from 'normal' is it reading ? First suspect would be sender but if it is twitching on ignition then usually it works .Only way to really know is to get a mechanical gauge and get a direct feed .

Hi Lee,

As we drove out this morning it was reading about centre gauge when warmed up at about 40 - 50 mph. Much higher on start up. I never saw it drop as such, I just noticed no movement when blipping the throttle, whereas it has always responded instantly hitherto. As I said, on switching on the ignition the needle moves, but it doesn't respond on engine start up. Maybe the sender has packed up, but perhaps I will have to get my self an oil pressure tester and as you suggest check the pressure directly. Are there any other symptoms I would notice if the pressure is down?

Paul

If it has gone tits up it wont be long before the warning light flickers but I'd not panic just yet and check the sender .No leaks ,no knocking ? I'd swap out the sender/mech test .If pressure has really gone then you can't do much about it anyway

Thanks Lee.

I've checked sender contacts - seem OK but if it is the sender then I will replace that. Mine has the large (about 1.5 - 2 inch diameter) cylinder with the smaller branched sender at right angles to it (one connector on each) - I guess Renault still supply them?

As for the pressure test, is it a standard tester that I could get from a motor factor? Or do I have to go to Renault?

When you say 'if there's no pressure there's nothing you can do', I presume that would mean a replacement oil pump - would that be correct? Joy.....

Paul

What I mean is if no obvious big leaks then it's internal ,pump,shells ,so no quick fix .Could be shite in the sender ? I'd take it off and clean .
I have a mechanical gauge if you want to pop over .Not sure how far away you are ? Lincs not that far away but dare you drive it ?I could poss do a RATS mobile trip .

Hi Lee,

Thanks again. I'm actually close to Newark (Notts - but only just!). I'll give you a call for a chat soon if that's OK?

Anyway, you make a good point about the sender - not that I really understand what's inside them, but this morning I started the car and the gauge indicated the same as yesterday to begin with. I then held a brass rod against the sender (just under the soldered contact point) and tapped gently with a hammer. When I went back to look at the gauge it had moved to about 4 or 5 mm above the centre point of the scale. However, on switch off it dropped only to the central point. Now when I switch the ignition on the needle rises to just below the centre! So something is sticking somewhere, and further gentle tapping has not yielded any change.

What should I clean the sender with - petrol, or any solvent such as thinners etc?

Cheers,

Paul

P.S. I did contact Renault to query viability/price of the sender, but although the part still appears in the UK Renault listings, it seems that it is a 'discontinued' part. Should be fairly generic - where might be best to acquire one from?

Paul, Follow the wire back from the oil pressure sensor to a connector .... according to the manual .... next to item 362 in your other post, mounted on the wheel arch. Might be worth checking and cleaning contacts of that connector. As the pressure switch is a variable resistive component, any lack of good contact in that connector will give you incorrect readings.

DSC_0434b.jpg

Thanks John, and Lee for all your advice thus far. Problem not resolved yet, but here is what I have done so far:

I took the original sender out and cleaned it as best I could - I have no idea what is inside an oil pressure gauge sender though! On re-installation nothing has changed. The gauge doesn't flicker with the sender disconnected, but once connected the needle goes to over the half way point where it seems to stay whatever the engine is doing. Of course it only moved to this position once I had tapped the sender just over a week ago. Tapping the sender doesn't made any difference now.

I ordered a new sender, listed for the D502, from Mecaparts and it came really quickly. Trouble is that it doesn't have the extended neck and oil 'port' to feed the oil pressure switch. Looks like the thread size is correct, so the sender will probably fit to the block connection OK, but unless I can attach the oil pressure switch to another 'port' on the block I'll just have a red light on permanently!



What would you suggest?

I haven't checked the oil pressure with a gauge yet as I don't yet have one, but the engine still behaves, and sounds absolutely normal, so I am pretty sure the sender is dicky. I have also chased the connections back as you suggested John, but everything seems clean and totally corrosion free - the car has done just 24K miles and I suspect has been fairly pampered for most of its life. In fact I'm finding clean metal to metal contact surfaces as I track down the earth points too.

Paul T

Paul, any chance the senders spigot (the extended piece) can be unbolted from the old sensor and transferred to the new one having unbolted the short one. It certainly looks as if you can remove it from the old sensor, but I can't see if it can be removed from the new one ?????

I ordered a new sender, listed for the D502, from Mecaparts and it came really quickly. Trouble is that it doesn't have the extended neck and oil 'port' to feed the oil pressure switch.

The sensor you ordered from Mecaparts, was the part number MP1 251, as the picture that accompany's that part number is for the correct design with the extended spigot.

Just for reference, I have just put a meter between the sensors connector and earth without the engine running, and I get a reading of 57 ohms (wiring still connected)

- I have no idea what is inside an oil pressure gauge sender though!

Just a quick aside on this. Inside the sensor there is a cavity bordered by the outside "dome" with the connector, and internally, a metal diaphragm. The cavity is filled with carbon particles which are resistive. Because they are particles the whole cavity can be compressed, and when you compress carbon particles the overhaul effect is that the resistance across the whole will drop as the area of contact between the particles is increased due to the pressure being applied, in this case, by the oil pressure against the diaphragm.
As the oil pressure increases so the resistance reduces ..... now attach that to a meter with a voltage attached to the other end of the meter, and you have an oil gauge.
Now I will leave you to work out why, after you "tapped" it with your brass rod, the reading on the gauge went up .... and stayed up.

John

You learn something everyday.
Thanks for that John. Was whined ring myself what was inside the cylinder.

Dave

The new sender you have is for the early turbo car that has only one sender

The new sender you have is for the early turbo car that has only one sender

Actually not, the early type sender had two contacts, the one I have pictured, that Mecaparts list for the later cars (including the D502) has just the one contact - hence my question about how to make it fit with the oil pressure switch sender.

Paul T

The sensor you ordered from Mecaparts, was the part number MP1 251, as the picture that accompany's that part number is for the correct design with the extended spigot.

Just for reference, I have just put a meter between the sensors connector and earth without the engine running, and I get a reading of 57 ohms (wiring still connected)

Now I will leave you to work out why, after you "tapped" it with your brass rod, the reading on the gauge went up .... and stayed up.

Thanks John,

I understand the sensor explanation, but unless there is a faulty diaphragm in my sensor I can't see why tapping it should have made any difference at all. Maybe that was just coincidence?

I agree in the Mecaparts diagram (which is effectively extracted from PR1132 anyway), the part they number as MP1251 is shown as the long neck sender, but their photograph is of what they sent to me. I'll have a look and see if the spigot on each will undo, but I didn't want to force anything and destroy either or both senders! Maybe someone out there knows definitively if this can be done? I've also emailed Mecaparts to ask how they expect the parts to fit in conjunction with the oil pressure switch; there has to be a solution........

I'll check the resistance too and see how it compares with your reading.

Paul

Paul,
Give Merlin motor sports a ring.
They have lots of adaptors to tee of etc for oil pressure and temp senders.
Not ideal but may solve your woes.
Dave