Lotus Elan

Oil Pressure Sender

PostPost by: billwill » Fri May 01, 2020 12:53 am

"resistor , mechanical adjustment " That's pretty much the broad definition of a potentiometer. They are not all nice round twiddly knob thingys.

A resistor with a sliding contact is a potentiometer as far as I am concerned.

Are you sure it is a bimetallic strip? That doesn't make sense, as such strips are temperature sensitive, not pressure sensitive. And those gears in there look rather similar to the gears that drive the pointer in a typical bourden pressure gauge.


LATER

https://www.howacarworks.com/accessorie ... uage-works

Ah, this page says the pressure pushes a diaphragm rather than a bourden tube, so I wasn't quite right, though why the lotus one uses gears in there is strange, I would think that reduces reliability.
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PostPost by: john.p.clegg » Fri May 01, 2020 5:02 am

Bill
Sorry mate but , there is no bourdon tube , resistor adjustment, sliding contact or potentiometer , it is a set resistor , the mechanical adjustment screw ( gears ) you can see adjusts the tension on the bi-metallic strip , which is heated by the wire wrapped round it , the contacts of which vibrate , just as the 10v instrument regulator...

John ;-)
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PostPost by: billwill » Fri May 01, 2020 12:45 pm

john.p.clegg wrote:Bill
Sorry mate but , there is no bourdon tube , resistor adjustment, sliding contact or potentiometer , it is a set resistor , the mechanical adjustment screw ( gears ) you can see adjusts the tension on the bi-metallic strip , which is heated by the wire wrapped round it , the contacts of which vibrate , just as the 10v instrument regulator...

John ;-)


Aye, I had sort of worked that out after staring long & hard at the photo last night., (after posting my message above). It uses a diaphragm and then the bi-metalic strip stuff is effectively a pulse width modulation of the pressure.

My basic thought though is still true: that is far too complicated & introduces unreliability. The bi metallic strip & heater would be temperature sensitive, so not a good thing to hang on a hot engine casing and also rather slow, so the dashboard pressure gauge will only show an average pressure and would take a second or so (guess) to show oil pressure failure.
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PostPost by: john.p.clegg » Fri May 01, 2020 2:17 pm

.. and it has been known to cause problems if the oil gauge is fed of the 10V supply for harmonics to develop , making the display totally unstable...

John ;-)
Last edited by john.p.clegg on Fri May 01, 2020 4:09 pm, edited 1 time in total.
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PostPost by: mikealdren » Fri May 01, 2020 2:19 pm

billwill wrote:When I heard that Plus 2s use an electrical pressure indication, I somehow naturally assumed that Lotus had done it for improved reliability.


My late (130/5) car had a mechanical gauge and the earlier (+2S) car had an electrical gauge. I suspect that the reason may have been reliability - with Lotus it was usually cost but I suspect the later setup may have been more expensive?
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PostPost by: Hawksfield » Sat May 02, 2020 9:10 am

Hi
I cut the can open on mine around 25 years ago cleaned the contacts and all is well today.
This was after trying to find a replace ment without success
I had problem with the terminal so fitted a lead wire and sealed with araldite, cannot remember why I had a problem with it maybe it was how I opened the can.
Anyway it's that long ago and still working I had forgotten all about it.
Give it a go Andy
Good luck
Regards

John

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PostPost by: Andy Hamblin » Sat May 02, 2020 10:09 am

Hawksfield wrote:Hi
I cut the can open on mine around 25 years ago cleaned the contacts and all is well today.
This was after trying to find a replace ment without success
I had problem with the terminal so fitted a lead wire and sealed with araldite, cannot remember why I had a problem with it maybe it was how I opened the can.
Anyway it's that long ago and still working I had forgotten all about it.
Give it a go Andy
Good luck


I think I will, thanks for the encouragement. Someone else has had a go before me and made a very messy job of closing it back up. There might not be enough good metal to re-crimp it, so may have to improvise with an new cover.
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PostPost by: JoeMan78 » Sat May 16, 2020 3:38 pm

Right, after a little bit of fiddling, delicately with a diamond file, wire wool and Stanley blades I got the old sender working again!
It does however read 5-10psi higher than it used to, but springs to life and gives a nice steady reading.
I also bought a gauge from ASAP supplies rated 60psi with 1/8npt thread which worked with the gauge albeit too a little extra wiring to get it operational.
Pretty easy fix Andy... give it a go!
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PostPost by: alanr » Sat May 16, 2020 3:59 pm

Well done getting it going again! :D
Curious to know what you resealed the sender back together with?

Alan.
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PostPost by: JoeMan78 » Sat May 16, 2020 4:06 pm

Hi Andy,
I used Araldite repair metal for good, clamped the unit together and used a small sausage of the stuff to create a bead around the can.
Seems strong enough, and because it sets brittle I should be able to chip it off if it needs any more repairs!
I would take a picture but it’s back on the car again and I’ve lit the bbq!
Best regards,

Joe
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PostPost by: Andy Hamblin » Sat May 16, 2020 4:52 pm

JoeMan78 wrote:Right, after a little bit of fiddling, delicately with a diamond file, wire wool and Stanley blades I got the old sender working again!
It does however read 5-10psi higher than it used to, but springs to life and gives a nice steady reading.
I also bought a gauge from ASAP supplies rated 60psi with 1/8npt thread which worked with the gauge albeit too a little extra wiring to get it operational.
Pretty easy fix Andy... give it a go!


Well done Joe, I will give it a go!
Cheers,
Andy
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PostPost by: Andy Hamblin » Sat May 16, 2020 4:57 pm

Also Joe - could you give details or a link of what you got from ASP supplies, as a backup?
Cheers,
Andy
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PostPost by: JoeMan78 » Sun May 17, 2020 3:57 pm

Hi Andy,
Its a Kus Unit - 5 BAR and will require you to run a wire from the ground terminal to another point on the engine block.

https://www.asap-supplies.com/gauges/se ... eu-npt-1-8

This unit gives continuity at rest and provides resistance with increasing pressure - the opposite to the original unit. Therefore the gauge will work in the opposite direction (low pressure reads high), but it did record 40psi on the gauge while running and responded well at tick-over and speed.

For £22 I thought it worth a try and allowed me to continue to use the car while I ran the repairs.

Best Regards,

Joe.
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PostPost by: Andy Hamblin » Sun May 17, 2020 5:29 pm

Cheers Joe.
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PostPost by: Andy Hamblin » Fri May 22, 2020 9:46 pm

I took the cue from Joe and opened the sender up, cleaned everything and sealed it back together with Araldite. It was full of crud because a previous repair had been made and it had not been closed up very well.

All seems well, it responds very quickly and displays the pressure at what seems like an acceptable level. I can't comment on accuracy because I don't know how much pressure the engine produces; the sender didn't work at all when I got the car.

Thanks to everyone who helped/commented.
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