I was driving today and right before I got home the oil pressure light flicked on and I looked at the gauge was at zero. The light immediately went off, but the gauge is stayed at zero. By all accounts it’s still runs fine and the light stays off, but the gauge doesn’t move. Any leads on where I can start and if I can still drive it while I troubleshoot?

I checked the oil level and it was fine. It was hot here today, but I doubt that makes an issue.

 

Remove the wire from the oil pressure sending unit. With the key "on" touch the wire to ground. The oil gauge needle should right up to the max reading. If it does then you have a faulty sending unit. If not you have a problem with the gauge, wiring, or IP circuit board

The oil light uses its own switch; smaller, right next to the sending unit.

A low idle speed might cause the light to flicker a bit, especially if the oil is hot

Low pressure at idle speed is characteristic of the V12s; generally nothing to worry about. Oiling system problems are not common on the V12s

Cheers
DD

 

Oil is kind of important to motor longevity.

if it was my car, I would buy a small mechanical oil pressure gauge and temporarily install it to the port (may require a flex line, or some various fittings to make it visible) where the gauge oil sending unit resides and verify you do have pressure before driving it. But thats just me, i dislike motor removal, rebuild and reinstall.

Or test as mentioned above and buy and install a new sender if necessary, but i sure wouldn't just 'drive the car as usual" until the issue is resolved.

Doug

 

Thank you both for the replies. I went out this morning and everything was back to normal. I did identify where the sensitive unit and switch are, so if it happens again I will troubleshoot. I’m wondering if I should maybe switch to a heavier weight oil for the summer, I’m not sure if it’s possible but I was on a pretty spirited run beforehand and it was about 90f yesterday, I’m wondering if the oil thinned to the point it caused the issue.

 

That depends on what problem you’re trying to solve for. Are you trying to solve for oil pressure or for engine health? What the engine really needs is oil flow to the bearings. Oil flow is kinda hard to measure, whereas pressure is easy. So pressure serves as a substitute in the gauges.
The problem with relying on oil pressure is that the viscosity of the oil changes with temperature. As it warms it becomes less viscous and therefore easier to move. The flow rate stays the same, the pump is going to move the same amount of oil hot or cold, but the pressure of the oil decreases. Using thicker oil will result in a higher reading on the gauge, so if that’s what you’re concerned with then it will achieve that. But thicker oil is harder to move and it will take longer to get to the components that need it. It’s not something I would do in my car.

 

Thicker oil doesn't squish out of the bearings as easily, though.

Thats why multi visc oils were introduced, they flow at lower temps, but act like heavier oil at higher temps. There is synthetic rubber dissolved in the oil to give it the multi visc characteristics

There is tradeoff on all things. Some modern motors use 0-20 oil (helps gas mileage with tight bearing clearances), my Ferrari calls for 20-50 oil. A typical 1970s/1980s Chevy motor would use 10-30 or 10-40

Your motor probably calls for 15-50, 20-50, 15-40, or there about for summer time use; what oil do you have in it?.

Doug

 

Jaguar issued a few TSBs for oil pressure gauges. They even replaced the senders with SWITCHES in the late 1990s.(it's a Ford thing)

Read and understand the logic.

 

A lot of V12 owners prefer 20/50. And the Jaguar shop manual shows 20/50 as acceptable for higher temp areas.

There are arguments to be made that the engine doesn't really need (or benefit from) 20/50. But we all know how oil discussions go.

I used to use 20/50 in the summer and 10/40 in the winter. Now I use 10/40 year round. Can't say that my life has changed.... nor my oil pressure readings . Not, at least, in any way discernable by me.

Both my V12 Jags have shown very low readings on the gauge at idle, hot. Over the decades many others have reported the same. Pretty sure that this is well covered in Kirby's book.

Installing a temporary gauge for an independent reading certainly can't hurt.

If you're running 10/30 or 10/40 you might try 20/50 and see what happens.

Cheers
DD

 

sad to say, I forgot what I put in at the end of last season. I’m pretty confident it was 20w/50. I know I based it on recommendations I saw in the forum and also the graph in the back of my owners manual.

I’m due for an oil change and bought the filter a few days ago, so if there’s a different rec instead of 20-50 I’m all ears.

ive been driving today with no issues. I just freaked a little when I pulled into my driveway yesterday and the light flicked on and I didn’t register pressure.