Oil Pressure Gauge, inaccurate

[John Quilter]

After many years believing my oil pressure was low, even after a comprehensive engine overhaul 2 years ago, I read about this Quality Classic (UK located) replacement gauge kit that is mechanical not electrical. To test I rigged up a T fitting to compare the factory gauge with a known mechanical one. The readings were significantly different, the car gauge being on the low side and getting worse recently. Knowing the sending units are known to be problematic, not to mention expensive, I bought the Quality Classic mechanical gauge kit and fit it. Now the gauge finally reads correctly, about 60 PSI on cold start up, 50-55 PSI hot at 1500+ RPM and about 35 PSI at a 650 RPM hot idle. The kit comes with a nylon tube, an identical to stock gauge face and an installation fitting, Fitting the gauge is relatively easy and the original light socket fits the new gauge even though one is provided in the kit. The most difficult part of the installation is finding a suitable location for the hole in the engine bulkhead. I noted the location of the vacuum tube for the scuttle vent was visible in the engine bay and behind the folding center dash panel so I drilled a hole in the bulkhead at the same level as the vacuum tube and about 2 inches toward the heater box. The hole will have to be about 1/2 inch in diameter to get the fitting through. Using a section of vacuum tube split down the middle I was able to push the fitting and tube through the hole and through the hardura insulation on the inside behind the electrical wires. A grommet will be needed to plug the oversize hole. I was concerned that there would be enough nylon tube to permit the dash to fold down but this was not a problem and I just ensured there was some extra slack behind the dash. Photo shows my test device permitting both a mechanical gauge and factory electric gauge to operate simultaneously for testing. Finally, after many decades of ownership, I am now confident of the engine oil pressure.

[cass3958]

Very interesting as my gauge is up and down depending on which way the wind is blowing. Not sure if I would fit one but it might be nice to buy one just to compare the PSI between the two. Do you have a link or name of the place from where you bought the gauge please.

[Glyn Ruck]

I see the gauges have a different scale. Why Jaguar got rid of the 100psi gauge to stop people worrying about oil pressure.

[John Quilter]

Cass, You can contact Tim Goldthorp at Quality Classic tim@classicquality.co.uk. If you are just wanting to verify your car's gauge and and a known accurate other gauge you could probably buy a generic one, the tube and the fittings such as I showed in my photo for much less than the Quality Classic kit. If you were local, I'd gladly lend you my test gauge set up.

Glyn, The face of this gauge and scale is exactly the same as the factory gauge. I suspect Jaguar went with a 0-60 PSI scale because the oil pressure by pass valve is set at 60 PSI (at least I think so) so theoretically the pressure should never go over 60.

[Glyn Ruck]

Sorry the range looks different on this gauge below. Must be my eyesight. Jaguar dropped the 100psi gauge to get readings up closer to centre of the gauge. Oil pressure always looked pathetically low on the 100psi gauge and worried customers. It was driven by customer concern.

Capillary Gauge..PNG (745.39 KiB) Viewed 383 times

[cass3958]

I think that is just the test gauge and the one he is using is the one in the box which goes to 60 psi.