Oil pressure, and what the sources disagree about

Oil pressure is one of the few numbers a buyer can read from the driver's seat, so it gets asked about constantly. It is also one of the figures where published guidance disagrees, and this article sets out the disagreement rather than papering over it.

What the two guides say

Magneto's Jaguar E-type market guide says that at idle the pressure gauge on the straight six should read 40psi. E-Type UK's buying guide says oil pressures should be around 45 to 55psi at 2,500rpm. These are different measurements taken at different engine speeds. A healthy engine will naturally show a higher reading with the engine turning faster, so the two figures cannot be laid side by side and reconciled, and the archive has not found a Jaguar factory specification to settle the matter.

What falling pressure tends to indicate

Oil pressure is created by a pump pushing oil through clearances. As main and big-end bearings wear, those clearances grow, oil escapes more freely and pressure falls. Low pressure at hot idle, when the oil is thin and the pump is turning slowly, is where worn bearings show first. A weak pump, a stuck relief valve or a blocked pickup can produce the same symptom, which is why a low reading is a reason to investigate rather than a verdict on its own.

Why the hot idle reading matters most

A cold engine on thick oil will show a strong reading on almost anything, so a seller's gauge check on a cold start tells you little. Let the engine reach full temperature, let it idle, and read the gauge then. That is the figure to compare against the guidance above, and the figure to walk away from if it is clearly low with the engine fully warm.