Nigelplug,
It is interesting to hear that you believe that an oil pressure of 15 PSI in inadequate at NWT (Normal Working Temperature?) when at idle a 4.2L XK engine.
I am merely a hobbyist and not a trained professional mechanic and I am always interested in learning more. I know that Jaguar specified 40 PSI at 3,000 RPMS when at operating temperatures, and the low pressure warning light switch is supposed to open at about 3-5 PSI to turn off the light. If more than 15 PSI is needed at idle, why did Jaguar use a 3-5 PSI switch and not one for 15 PSI or more?
I am always interested in learning more about these wonderful cars. Why do you believe that 15 PSI is inadequate oil pressure at idle when the engine is warmed up?
Hi Paul
Because in reality that tells me there is too much clearance between either/ or both the crankshaft main and big end bearings. Unless the oil pump is very worn? A worn oil pump will always lose efficiency at higher temperatures.
Kurt,
Yes, the part you have circled is the oil pressure relief valve. I have disassembled, inspected, and reassembled a few of them but never found anything that I thought was wrong. Others will have to provide more details on adjustments as I have never done that.
Yes, the part you have circled is the pressure switch (C42200) that closes and turns on the low oil light on the dash when engine oil pressure gets below 3-5PSI.
The variable resistance oil pressure sender (C46272), that provides the signal to the oil pressure gauge on the dash is a small metal cylinder located above the oil filter on the right side of the block. The attached picture shows the current set up in my 1969 E-Type with the original sender circled in red and the new aftermarket sender circled in green with both installed with “T” adapter.
You will note that I have also installed a spin on adapter and a modern oil filter instead of the original metal canister type with the removable paper element.
**
The adjustment, if required, is using shims to increase spring tension, Paul…
I haven’t found any specs for relief pressure - rumour says around 65 psi? As far as I can see; the only relevant test is to rev the engine with cold oil - when the pressure rise stalls, the relief valve opens; relief pressure is reached…
But the main point is that the valve was installed to prevent excessive oil pressure at any time…
I remember 65 as well, and I‘d go shim after shim. Mine stays peaked at 40 and I don’t know whether that’s an actual value so a tee‘d in connection is a great idea.- I might look into it someday but it still takes me a few hours to get the valve out because I have an RHD.
Bottom line, if the oil pressure with thick cold oil won’t go up to 60, shimming the RV is a good first step before tearing everything apart or being in constant annoyment because pressure is low!
I maybe way off here, but always thought the oil pressure RELIEF valve was in the filter head? What’s shown in the pics here is a gauge sender unit not a relief valve?
Nigelplug,
You may have the pictures and posts confused. Kurt attached a picture of the engine of his S2 XJ6 to his post with the words “Relief Valve???” on it. I replied and confirmed that his picture did correctly identify the relief valve at the bottom of the filter head. Then in my post I attached a picture of the current setup in my 1969 E-Type FHC showing the aftermarket oil pressure sender installed redundantly with the original oil sender by use of a “T”. Does that clear things up?
**
Or indeed get a ‘second opinion’ with an external pressure gauge testing, David…
But you are right, of course; while the testing spec says minimum 40 psi at 3000 rp ms, it does not mean that more pressure is required at higher revs. The relief valve is there to prevent excessive pressure, which is harmful - if the valve relieves at too low pressure, the pressure may be too low for comfort at higher revs…
I would check the pressure relief valve to make sure it is seated properly. And check that the ball isn’t knicked, I had that in my ‘66 ‘S’ and every now and then the pressure would drop. Invariable on the return trip of a run
Following numerous frustrations with OP readings in my 420G with original motor (ie reads 0)
Installed a digital (can be teed or direct replace), about $40
It revealed SO many interesting things…including the motor needed replacement/overhaul
registered crank pressure at 4psi (old and new motor)
I fitted an idiot light, none had been there…extinguish at 5psi
digital gauge has a 10psi red light
cold start pressure 55-58psi in both motors
general running pressure (above ~2000rpm) ~38psi in old motor ~55psi in new motor
hot idle 30-40psi new motor…8-15psi old motor!! @~750rpm
I also noticed on the old motor, idle pressure plummeted on a steep slope!..level was not low
a mechanical gauge would give you nearly as good reading as this, but NOT instantaneous low pressure readings…the instantaneous digital pressure reading shows if OP is falling to a level that worn bearings are in play imo. I do not think a needle gauge will show that.
a mechanical gauge is more expensive, and difficult to fit, oil line under dash etc
I guess one lesson to learn is dont ignore a zero OP reading
