The 'E' Type Forum

I've run out of functioning original oil pressure senders.

I bought one recently (C15474*/1) from one of the usuals after being assured that it would work with a S1 E type.

It doesn't, of course. It takes forever to come up to pressure and only reads about 20psi with a known test pressure of 40psi. It looks identical to the unit in my XJS.

Has anyone found a source of senders that actually work?

Andrew, could this help?
https://www.smiths-instruments.co.uk/se ... ransducers

Geoff

Thanks. I'll follow that up with them.

Ha, welcome Andrew, to the line-up of losers.
This web page pretty much nails it.
http://www.projectetype.com/index.php/t ... -test.html

Re Geoff’s Caerbont chart, for Jaguar:
Pre V12 = 60 psi = C15474 use PTR1801-06
Early V12 = 80 psi = C31177 use PTR1811-10
Later V12 = 100 psi = C46272 use PTR1801-10 or PTR1001-10EC (the latter is more linear)

You have a 60 psi gauge however you can get satisfactory results with a different range sender, for example the above recommends a 100 psi sender for an 80 psi gauge. If you are desperate, it is possible to tweek the two screws on the back of the gauge, you do need to dismantle to figure out the non-intuitiveness, but it does mean there are more options than the above. Tweek too far and the needle falls off its pivot, don’t despair, can be recovered ...


Note some of the Carebont senders are defined as having “euro winding”, these will cause yr gauge to display incorrectly. Basically there are two standards, the American marine standard uses zero .. full scale = 240 .. 33 ohms, the European marine std is zero .. full scale = 10 .. 180 ohms, i.e. euro is virtually inverse to the American std that Jaguar oil pressure gauges depend on.
https://fariabeede.com/site_manuals/IS0 ... %20rows%20

The trouble with trial and error is that each sender is the best part of $100 so experimenting can get expensive ...


The old Smith gauges are part of the problem, they are non-linear. Most modern senders have a quite linear response so the best you can achieve, with a new sender and an old Smiths gauge, can be with significant mid range inaccuracy. The local Caerbont agent tried to reduce this by printing up a different face for my gauge, but not good enough even after squishing the critical low pressure end of the scale too much for my liking ...


The last Caerbont PTR1811-10 that i purchased couldn’t detect any pressure below 25 psi. SNGB advised, “this is a known issue, here is your money back, you can keep the sender”. After unsuccessfully trialling all potential Caerbont senders I tried a VDO sender, this worked well enough. P/N 360-801, one of the very few 240-33ohm VDO senders:


Only problem, VDO senders are taller and, with the thread adapter (85 mm high, 45 mm dia.), couldn’t be installed where I want it to be, in the original hot spot down on the back left side of the V12 block. So if you want to give this sender a whirl, PM me an address and I’ll stick it in the mail.

My sol’n is to try latest tech, I’m using a Bosch 0261230340 pressure & temp sensor, via ecu I/O that will be calibrated so gauge displays exactly what the sensor detects or, channelling my inner zaphod Beeblebrox, whatever maintains my cool ...

I note Caerbont still manufacture the Jaguar style of Smiths 60 psi pressure gauge. I wonder how accurate a matching new gauge and sender would be? If the above doesn’t work, something I might look into. Or the mechanism from a cheap-as-chips ¼ sweep VDO gauge, retrofitted upsidedown into a smiths casing. It’s on my bucket list, accurate Jaguar electric oil pressure indication before I die ...

lowact wrote: ↑

Sat Jan 22, 2022 4:07 am

Ha, welcome Andrew, to the line-up of losers.
This web page pretty much nails it.
http://www.projectetype.com/index.php/t ... -test.html

LOL.

That's my website :-)

The problem is that the original Smiths gauge is just a heavily damped ammeter, and the sender doesn't work by variable resistance at all.

It has a sprung bimetallic strip in it, and the strip acts a switch. It is closed more the higher the pressure, thus delivering more (average) amps to the gauge, so the needle goes up.

Clever but totally daft.

It is possible to alter the guage reading by simply fitting a resistor in parallel to the guage input.....so connect beteeen i/p and earth.....depending on the resistor value you can alter the amount of curren that ill flow tbrough the guage....typically the sender/guage will under read so more current through the guage makes the guage read higher.............start with 150ohm its simple to do........just connect at back of guage.....Steve .....ps becaus your setting up a parallel resistor cct the higher value resistor you use the more current will flow through the guage thus giving a higher reading

I did that for the temp sender - tried loads (even a matched set of sender & gauge from caebont) but could only get a realistic reading with a resistor in line.

A resistor in line....i presume you mean in series with the guage will reduce the current and make the guage read lower......the resistor needs to be in parallel in the circuit the make the guage read higher.....Steve

Yes, in series to reduce the reading by 10 degrees.

abowie wrote: ↑

Sat Jan 22, 2022 6:28 am

The problem is that the original Smiths gauge is just a heavily damped ammeter, and the sender doesn't work by variable resistance at all. It has a sprung bimetallic strip in it,

Not what you bought? C15474’s are now PTR type, PTR1801-06? Never were originally of course.
Fyi my goto reference for Smiths senders, recommended:

https://www.triumphclub.co.nz/wp-conten ... _2_2v0.pdf

E-type wiring diags have the electrical connection to the oil pressure gauge from the input (= unregulated) side of the instrument voltage regulator. This verifying that e-type design was for bi-metallic type of oil pressure senders, Smiths “PT” type. Now there are only resistive types available (e.g. Smiths “PTR”), so the oil pressure gauge electrical connection should be from the output (regulated) side of the IVR. Same for earlier cars I guess ...
Here is PT (left) and PTR (right) mechanisms. Apparently you can pop the sender tops off and on, I use angle grinder and araldite.


My understanding, apart from the regulated versus unregulated voltage issue the two types are notionally interchangeable, they both vary resistance according to pressure. The resistance range, zero..full scale = 240..33 ohms, is applicable to both types (its the design std). That resistor in the PT sender is in parallel with the bimetallic, dictates the full-scale minimum, is 31.5 ohms.

Imo only notionally interchangeable because, and this is my fundamental issue, there is different linearity. With PTR’s the resistance versus pressure characteristic is pretty much a straight line. With PT type it is curved. I need curved because the characteristic for my gauge (indicated pressure vs sender resistance) is curved, I guess for the same reason that the PT sender characteristic is curved, it uses a bimetallic. The bimetallic in the gauge is physically very similar to the bimetallic in the PT sender so the curves would be similar so the gauge indication would have been reasonably accurate at all pressures. With bimetallic senders now NA, we are reduced to trying to match linear senders with non-linear gauges. Smiths website says “we manufacture pressure transducers to the original designs” – ha!

Adding a resistor, imo not a solution, best this can do is to move and reduce the very narrow range within which the gauge is then accurate. You have to decide, where do you want it to be accurate, to help u make an engine off decision? There’s an idiot light for that. In Andrew’s case, I suspect a resistor in parallel to the gauge wouldn’t make any difference, would need to be in parallel with the sender, i.e. from the sender side of the gauge to a convenient earth (assuming the objective is accurate indication at 40 psi and generic OEM gauge and PTR sender characteristics).

So many options:
Find a matching bimetallic sender (dream on),
Repair yr old sender (angle grinder & araldite),
Make do with one of the available senders – don’t limit yourself to Smiths, tweek the gauge, calibrate it and play with resistors.
Buy a new classic style electric gauge and sender from Smiths – only if its a linear gauge and the guaranteed accuracy is written in gold leaf.
Buy any other brand of ¼ sweep pressure gauge and matching sender, mount the guts of the gauge upside down behind yr Smiths dial,
Translate (map) yr sender resistances via a suitable black box – is what I am doing,
Fit a mechanical gauge like everyone else.

I've read all of this, and the linked stuff from Triumph NZ, but I can't honestly say that I can understand how a non PT sender can work accurately with a gauge that is essentially an ammeter.

I can see that people have managed to jury rig a non PT sender so that it will read an acceptable single number on the stock gauge, but surely this is just a random event rather than a linear and reliable expression of the actual oil pressure.

I've opened a couple of old senders that I still have, and they are pretty easy to calibrate to a known pressure.

I think that the "grinder/araldite" technique is going to have to do until someone makes a clever modern electrical interface.

Hi Andrew.......fitting a resistor as i described in a post above is just altering the calibration resistance (saves you opening the sender to change the calibration resistor inside it)..... ...it dosnt fix the guage at one poing but is a way of calibrating you guage/sender to a known oil pressure that you would have had to test previously with a wet guage.........these sender/guage units are not ment to be acurate measureing devices purely indication of pressure......Steve