Oil Sender Unit diagnosis

I have a 67 OTS Series I. The Oil sender is acting up (suprise suprise). My question is whether the needle should move when turning Key. It rises to around 30PSI. When I start the car it slowly rises to above 60 psi and remains there upon running. Seems like it should be at zero until car is running. At least that’s what my old TR6 used to do.

I recall using teflon tape on the threads to prevent oil leakage. Perhaps I have a faulty ground. The unit itself has a second spade. Is this to ground???

Before running the re-purchase of sender unit route, I though I’d test the waters.

Thanks in advance
Mark, San Rafael

If you mean, “moving the key,” and the engine is not running, no, that’s not correct.

Yep…I meant moving the key…

Any idea if this is a wiring problem, unit problem, or user problem.:slight_smile:

Do you have an aftermarket mechanical…teflon tape on the threads ?

its a reproduction of the original style that sends signal to the gauge.

It’s the sender, this kind of fault is always the sender. I had one sender that developed this fault very quickly. I have another that under reads, one that doesn’t read at all and one, just one of four, on the engine now, that is consistent and close enough to accurate for me to rely on.

It might be the regulator which adjusts the voltage to 10volts which supplies the oil and temp gauges. These were certainly fitted to cars with dynamos, not sure about alternators.

That regulator was also fitted to the 4.2’s.

Good morning,
The IVR ‘serves’ the fuel and temp gauges, the oil pressure gauge takes it’s current from the Battery lead on the IVR. JM2CW

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Wot LL says … and for those into the minutiae of these things, the original style of oil sending units has the voltage regulation built into the sensor, similar to the IVR vibrator in principle. So hooking that to the other IVR would end up in a series vibrational mess of harmonics.

So, I grabbed a random resistor from the local electronics store and rigged up a couple of clips and attached it to the sender unit. Instead of starting at roughly 35 PSI when I turn the key, it is now starting down around 15 psi. I’m not a EE so, all i know is the starting point is lower. Seems like an ok result to me. but… am I heading into disaster,if I start the car and run it to see if the guage gives reasonable.readings. Trial and error to get the proper resister…

I will check with a mechanical gauge later. Just wanting to know if I’m creating a problem. Im struggling with sending the usual supplier more money for a gauge that will actually work.

After having a laugh, thoughts appreciated…

San Rafael

Mark, SNG have just received a new set of OP senders from the UK? They sending me one for free because my previous one only lasted 11 months before it started showing erratic readings. They are warranted for 12 months. BTW this is my 4th sender in 4 years all from different vendors. At least SNG are honoring their warranty.


Ray better hurry up and fix this

No need. I’m going to get a new sender.

at the mercy of the suppliers

My S type does the same thing - starts at 20 with ignition only, rises to full scale 60 for most of the time on the run, occasionally erratic by floating down to 20 or so when cruising and wandering back up to 60 when it feels like it. I have ordered a replacement from Barratt’s and hope it gives me more confidence and an accurate reading. It’s occasions like this that one appreciates the old-fashioned analogue technology. Far more consistent and reliable.

Then there is the left tank gauge. It rises to 1/4 and stays there whether full or empty. (The right one doesn’t have tantrums.) No doubt the sender again. I’ve ordered one of those too.

By the way, I am a life-long member of the IHE Club. (= I Hate Electronics).

Does anyone have a photo of a disassembled OP sending unit ? I’m getting really curious about them…


I bet @Ray_Livingston does.

I’ll gladly tear mine apart for you

Best Mark

I don’t have any pictures, but it’s a very simple device. Oil pressure pushes on a plastic diaphragm. That diaphragm has a contact on it, which gets pushed up as oil pressure increases. That contact is grounded, and makes contact with another contact at one end of a heated bi-metal strip, the other end of which is connected to the gauge. This creates a PWM output signal - the gauge sees either a connection to ground, or an open circuit, with the signal changing state several times per second. Increasing oil pressure leads to increasing PWM value. So, at low oil pressures, the gauge is grounded for a short period, and open for a long period. At high oil pressure, it is exactly the opposite.

Ray L.

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PCBs are due to show up on Monday…

Ray L.