Oil light on for no apparent reason on 1956 Thunderbird
 

I took my 1956 Tbird for a spin and noticed the oil light was on. No oil leaking on garage floor. Oil level is good. Car seemed to run just fine, temperature was good.


Background: This engine has very low miles since it was remanufactured. I replaced the oil sending unit last year when previous one was pouring out oil. I ordered a new one (since they are cheap and easy to replace) but wanted to ask what else could make the light come on?

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

Check with quality gauge!

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

No necessarily low oil pressure. I would suggest pulling a valve cover and look at the oil coming out on the rocker arms and overflow tubes and the amount of oil in the valley of the head. . If this is ok, then most likely the sender is bad.


If you ran the engine for some time after the light came on, then most likely the sender. Engines do not last long with bad oil pressure. But do the checks first to make sure.


I have had senders go bad and did the checks noted above to see if I could pinpoint the cause .


Checking pressure with a mechanical gauge is a good idea.


It is always a scary moment when you see that light go on when out driving.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

If an engine oil pressure light displays (for any supposed reason), you stop the car.

Just because the engine has been rebuilt, there is a possibility of a failure or poor assembly.

You have to determine proper oil pressure at that moment and diagnose from that point.

A FYB is tough but it ain't that tough.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

As mentioned, the sensor switch could be defective. There's a fair chance it was made off-shore.

The Oil light is triggered when the sensor (or the White/red wire to it) is electrically grounded. So if anywhere between the back of the Oil light socket and along the wire to the oil sensor, that wire is accidentally grounded... the Oil light will turn on. It could have gotten stuck to a hot exhaust pipe???

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

Unplug the wire to the sender. If the light goes out, it’s probably the sender, which is really just a switch. Replace. If it doesn’t go out, start tracing the wire back to the bulb, looking for where it’s grounded.

While you’re replacing the sensor, you can put a T fitting in, and have a place to connect the oil pressure tube for a manual gauge. Lots of gauges come with a plastic tube. Buy copper, but put some strain relief coils between the sender and the firewall.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

... hmmpf ...

Pull a rocker cover off ... pull the sender wire ...

Where is that OWNERS MANUAL?

OH! Here it is ...


Yeah, that is what I would do, remove a rocker cover or two and pull the wire ...

How much does a new engine cost these days anyways ... :rolleyes:

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

I was mechanic for 30-years. I have a bunch of spare mechanical Stewart Warner gauges I can screw in place of the sending unit and verify the oil pressure. "Most" of the time it's just a bad sending unit.

I had '57 T-Bird my mom bought new and then my grandfathers ended up with it. When he died, I ended up with it, all original, original paint. nice-nice car. Stupid me I sold it and it went into a private museum. I just didn't have the room at the time to keep it. Eventually I built a 2500 sf garage and now it's full of old Fords.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

Thanks for all the suggestions. I bought an inexpensive oil pressure test kit on Amazon and performed a test. It appears like I had 40-60 psi. The strange thing is the gauge did not hold the reading after I turned off the car. Since it had a pressure release button like a compression gauge I figured this was not normal. The gauge was kind of bouncing between 40 and 60 so I’m guessing the fittings on the test kit may have been leaking but I still thought the gauge should have locked in on the highest value until I pressed the release button.

I assume by seeing the gauge jump to 40 right away that I’m OK and just need to replace the sender?

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

... hmmph ...

Never heard of an oil pressure gauge having a pressure release. It showed zero at engine shut-off, it is normal.

Correct.

It is much better to be safe that sorry, or in new terminology, FAFO.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

Question. Are you saying it was bouncing between 40-60 at constant speed? Or was that from idle to higher rpm?

I also have never seen an oil gauge with a pressure relief.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

Maybe I made a bad assumption, but here is a picture with what I thought was the release button circled. It’s obvious that this was the first time I tested the oil pressure.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

That is not a pressure gauge, it is a manometer -

https://www.thomasnet.com/articles/i...how-they-work/

You need a quality pressure gauge. Below is a selection of cheap and not so cheap -

https://www.amazon.com/oil-pressure-...ressure+tester

You have the correct WORKSHOP MANUAL for the BIRD?

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

The one I bought was the third one in the list and looked similar to many of the ones in the list. Here is the description:

Mechanical Oil Pressure Gauge Kit - 0-140 PSI Oil Pressure Tester for Car and Truck Engine Diagnostics, Accurate Oil Pressure Gauge and Tester Kit.

The pictures attached are the kit I bought, the second kit in the list, and a picture of the tool in the second kit that looks identical, also with the pressure release valve. Almost all in the list have the pressure release valve except for the very expensive kits. I don’t know why the picture of the gauge I posted earlier said it had a manometer tube as the other kit photos did not have that description on the similar photo. Was it an error in the text on the photo? Was it just referring to the tube (hose) and not the actual gauge? The actual gauge in many of the kits I just reviewed look identical.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

... whew ...

What I see is a COMBINATION GAUGE, fluid pressure and manometer (inner gauge).

I understand the release valve as it would be a nice feature during certain diagnostic procedure(s). I have just never seen one on an automotive gauge.

When you started the car @ idle, exactly what did the gauge read? Was it a constant final reading or did the reading deviate? If that release valve was operational, it would have held the highest reading.

You need to understand that when you buy OFF-SHORE JUNK, results may vary greatly. Try it again and keep @ idle. Get exact reading. If the reading jumps, you may have a bad pump, relief valve or defective tester gauge.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

I have it all sorted out now. It showed 40 psi at idle. The gauge worked much better after it warmed up. I had a little trouble attaching the wire to the sending unit because I forgot you don’t just slide the clip straight on but start the end of the sender unit at the back of the clip closest to the wire and slide it on from there. The oil light on dash now works as it should.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

So it was a loose connection @ the switch all along?

It is still important to verify correct pressure when coming across a problem like this.

So possibly the pressure was @60# on initial start and once warmed @40#?

She's healthy.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

No, it was the sender. The wire was tight on the old sensor. I just had a problem getting the wire on the new one.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

OK ...

Was the replacement switch any different in design (@ connection) than the one removed?

Just trying to figure it out.

Glad to hear you got it solved.

Re: Oil light on for no apparent reason on 1956 Thunderbird
 

I imagine the new sender may have had a slightly thicker terminal but the main problem was I forgot how to connect the wire clip. I first tried to just slide it on but after searching for how was reminded you start the end of the terminal into the back (closest to the wire) of the connector and slide to the end of the connector.

The sending unit I bought this time was way better than the prior one that I believe I purchased from one of the Tbird specialty suppliers. I bought it from Rock Auto that had 3 to choose from, each a little more expensive (still under $10). The best one had a description of:

Standard Blue Streak delivers heavy-duty improvements not featured in the original, making it the perfect match for any technician who commands the very highest quality.

Features & Benefits:
- Mica-filled and brass plated polyester body resists heat, moisture and chemical corrosion
- Dual diaphragm provides extra assurance against leaks or bursting
- Teflon coated threads ensure the perfect seal and make installation a snap

The quality was very evident.

When I redid the oil pressure test all went well. It showed 40 psi (or slightly more) at idle, especially after the engine warmed up and idled smoothly.