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#21 Re: Oil pressure gauge

Posted: Sat Mar 28, 2020 4:14 pm
by jagwit
Today I cleaned my one workbench.... and found a Smiths 80psi oil pressure gauge. I suspect I bought this from a boot sale when I was rebuilding the E-type for a friend. Measured it up using my variable voltage power supply:

The needle did not move freely, but tapping the gauge with a pencil would cause the needle to find its natural position.
Jag oil pressure gauge values.jpg
Jag oil pressure gauge values.jpg (28.34 KiB) Viewed 736 times

#22 Re: Oil pressure gauge

Posted: Thu Jun 25, 2020 1:42 pm
by lowact
With confidence buoyed by the fading of memories of past failures I have embarked on the next great challenge, accurate oil pressure indication. Now I know that the consensus of the enlightened is to ditch the electric gauge in favour of a mechanical one, to the extent that SNGB now stock them as upgrades, but where is the challenge in that? This of course is the gauge in question, OEM Jaguar part number C33118:
Connected a variable resistance and measured the calibration, ohms versus indicated psi, the blue line in the graph below. Was a bit disconcerted by the nonlinearity, till I found this topic where Phil has measured similar (= orange line), so I guess that’s how it is.

Jaguar part number of the sender for this gauge is C31177. According to Smiths Instruments UK website ( ... ransducers ) this is a PTR1811-10, which is what SNGB send when you buy a C31177.

Trouble is it never worked properly, was almost all the time pinned off the end of the scale except, when steaming hot and idling, it might drop down as far as 60 psi. And now it has died.

Smiths agent in Aus is Howard Instruments. Howard is a nice bloke, I send him pic’s of my gauge and my characterization data and he sends me pic’s of his test bench showing his recommended sender, PTR1001-10EC, making an old Smiths gauge read close to 100 psi correctly.
Until my persistence that this might not actually be proof of anything became irritating, then all he would send me was an invoice.

PTR1001-10EC sender duly arrived, hooked it up to the air compressor and measured its characteristic, the yellow line on the graph below. To read this graph, example as per the red arrows: Oil pressure, when it is 47ish psi, will cause the sender (yellow line) to have resistance of 180 ohms which will cause my oil gauge (blue line) to indicate about 13 psi. Not so good.
MLBS3V12 wrote:
Thu Feb 20, 2020 5:57 pm
Hi all, I've a question on the oil pressure sensor. I do use the one from the XJS V12 engine on my E Type. At idle pressure read on the gauge is close from 20 lbs only. I suspect that the sender must be changed for an E Type one. Thank you for your remarks.
Michel, I’ve never had an e-type oil pressure gauge that worked correctly. But from what I’ve read, 20 psig when warm at idle is what it should be, can anyone confirm this?
And Michel, please can you advise, what is the part number of your oil pressure sender?

#23 Re: Oil pressure gauge

Posted: Thu Jun 25, 2020 2:42 pm
by MarekH
So if you hook up two of these yellow line gauges in parallel, then it'll halve their total resistance. Plot the new yellow line on the graph and you'll see it is now a reasonable match to the blue and red lines.

For example, at 30psi, the old yellow 240ohms now reads 120ohms; at 50psi the old yellow 165ohms now reads 82ohms; at 15psi, the old 290ohms now reads 145ohms, etc

There is little need to consider anything above 75psi in any great detail, as the pressure relief valve will cap the value.

kind regards

#24 Re: Oil pressure gauge

Posted: Thu Jun 25, 2020 2:56 pm
by MarekH
You can of course reach the same point by starting from the opposite end.

The sender has twice the amount of resistance wire that it needs for the gauge, so you could make the parallel argument (adjustment) at the gauge end instead - drive two gauges, one of which is left hidden. That way, the proportion of voltage drop between gauge and sender is brought back the required equilibrium again.

kind regards

#25 Re: Oil pressure gauge

Posted: Fri Jun 26, 2020 2:40 am
by Nialls Shortbear
Dear Mr. Simon,

I don't know if you sorted out your problem with the sender unit after all the responses.

We had the same thing with the senders going full scale when faulty, and also the same thing with them being positioned in that most ludicrous spot down by the exhaust. Later models they moved the small manifold to the top as mentioned. You might consider this most crisp upgrade from Rob Beere in Coventry which we fitted twice now as it moves the gauge sender and switch location to the later convenient position using some nice stainless braided hoses instead of those tiny oil feeds that lubricate the cam shafts (for me the weakest part of v12 design, why couldn't this have been internal?) You can block the old ports with 1/8" NPT plugs ... #Camfeed12

(picture added)
ali bongo.jpg
ali bongo.jpg (199.82 KiB) Viewed 565 times
Then, if you want to go to a mechanical gauge like everyone recommends, you dont have to mess around behind that nasty old LHS exhaust crawling around and stuff. On the block that they send, there is spare port so you can also add an Oil Temperature Sender!!!! Wayhay!!!! We like adding gauges, feeling that the V12 ought to have at least 10.


#26 Re: Oil pressure gauge

Posted: Wed Aug 19, 2020 7:20 pm
by 73ET
I had a sensor fail. Purchased a new one from SNG. This read 90PSI cold. Purchased a mechanical gauge - reads 55-60PSI at 3000RPM and 20-25PSI at idle.

#27 Re: Oil pressure gauge

Posted: Thu Aug 20, 2020 3:46 am
by lowact
90 psi when cold, does that mean ignition on but engine not running? What is the part number?

I was delaying reply to this post. My sender and gauge are still with Roger Howard of Howard Instruments, Caerbont Aus agent. Melb stage 4 restrictions have locked them out of their premises. Last report Roger was finding it was the age of the gauge was the problem, needed to be recalibrated. This seems plausible, explains the unexpected non-linearity of the gauge characteristic, compared to the new sensors linear characteristic.

When I finally get my electric oil pressure indication working properly, i'd prefer the sender in its original position, tucked up under the exhaust manifold, since I won't ever need to accessed again :lol: and because i don't want it restricting access to my HE spark plugs (and placement of 12 ignition coils).

Except that the later arrangement (sender on top) uses a larger diameter feed pipe, not sure if this is to stop pressure pulses to the gauge of if it was to improve oil flow to the cam-shafts, below is comparison:

I see that Rob Beere (thx NS) also has braided hoses for cam shaft oil supply without the sender. Does anyone know if inadequate oil supply to the cam shafts was ever an acknowledged problem? I am senstive to the probability that I might be the first person to upgrade to HE while retaining the original cam-shaft oil supply pipes ...