Oil pressure light 56 Tbird

[RichW]

Just come back from a short journey and as I was waiting to pull into the garage, the oil pressure light flickered on. Went out when I pressed the throttle. Checked oil level before journey and it was fine. Faulty sender or pump maybe? How do I check?
Thanks

This page contains affiliate links for which I may be compensated. As an eBay Partner, and Amazon Associate I may be compensated if you make a purchase at no cost to you.

 

[Pink T-Bird]

The gold standard is to remove the sender for the dash light and put a high quality gauge on it for diagnosis. You likely need a lift for this to get access, so you may need to take it to a mechanic. I believe on these engines, when hot, should be >20 psig at idle, but as long as it was above 12 or so I'd just switch to a heavier oil or viscosity modifier to postpone the inevitable. Cold start will typically be >50 psig (cold engine and fast idle) in a healthy engine. The dash light typically comes on a <10 psig IIRC. Depending on what the test with a guage tells you, you will know how to proceed. Pray for a bad switch, it's the only cheap option.

 

[CSPIDY]

The oil pressure light is looking for a ground to put the light on.
you will want to check the wire from the light, to the switch located on the left side of the block near the oil filter for shorts to ground.
Not vey likely but possible
Also as Pink T has suggested an oil pressure gauge is prudent
I installed a tee to provide a gauge and keep the light as well.

 

[RichW]

The oil pressure light is looking for a ground to put the light on.
you will want to check the wire from the light, to the switch located on the left side of the block near the oil filter for shorts to ground.
Not vey likely but possible
Also as Pink T has suggested an oil pressure gauge is prudent
I installed a tee to provide a gauge and keep the light as well.

Ok many thanks CSPIDY

 

[RichW]

Ok many thanks CSPIDY

If it is low oil pressure on the gauge would you look to change the oil pump first?

 

[Pink T-Bird]

If it is low oil pressure on the gauge would you look to change the oil pump first?

It depends on what you find with the gauge. If the cold start pressure is low and decreased very little as the engine warms up then you may be lucky and it is the oil pump, for example a broken or collapsed relief valve spring. If it starts out reasonably high like 40+ psig at cold start/fast idle and drops to 10 - 12 at warm idle I'm afraid it's rebuild time. Somewhere there is a worn bearing(s). You may be able to postpone the inevitable for a few thousand miles by installing a high volume oil pump. You would be flowing more oil to keep the worn bearings awash in lubricant to keep the pressure up in the rest of the engine, but the only cure is bearing replacement. I got almost 3,000 more miles out of a 351C doing that, but in the end all I did was postpone the inevitable and increase the cost of the rebuild. About 10 years ago in a '59 full size w/292 engine with low pressure I decided to replace the oil pump to limp a long for a few thousand miles. While I had the oil pan off I pulled a couple main bearing caps and found them to be worn quite significantly. Replaced the main bearings and oil pump with the engine in the car, but that only gained a modest increase in oil pressure. Basically, by the time the mains are worn out the cam and rod bearings are likely in similar condition.
Sorry to be the bearer of bad news. Like I said initially - pray for it to be a bad switch!

 

[RichW]

That's great advice, the gauge lands on Thursday, so fingers crossed for a good result. Engine sounds nice and has plenty of power so I'm hoping for the switch. Thanks Pink TBird

 

[Pink T-Bird]

The other (low probability) cause could be a partially plugged oil pickup screen. This is on the tube that sucks the oil from the pan into the oil pump. I would expect it to look like a bad oil pump with the gauge test.

 

[doug7740]

If it is low oil pressure on the gauge would you look to change the oil pump first?

You have gotten some great advice from the people on this forum, so wait until you have the oil pressure gauge readings before you start talking about replacing the oil pump. Since you don’t have the actual oil pressure specifications, the following is from Roger Fuller, who is the 1955 Thunderbird Technical Editor for the Early Bird Magazine.


“The specs call for 45–50 lbs of pressure at 2,000 rpm with a hot engine. Some documentation I’ve read stated that the light does not come on until the pressure reaches 5-psi. However, when both the light and gauge are hooked up, my experience is that it will start to flicker at about 10-psi. Yes, it will go lower than 40-psi at hot idle. The lower the idle speed, the lower the pressure. Even hot summer days and hotter than normal running temperatures can thin out the oil. Anything that restricts the flow ends up in reduced pressure at the sending unit. It can happen from a blocked inlet screen in the oil pan or gummed up passageways within the engine. And yes, a weak or incorrectly repaired oil pump can cause the pressure to drop at idle as well.”


Check the obvious first:

• When was the last time you changed the oil and filter?
• Do you have sufficient oil in the engine and are you using the proper oil?
• Did this problem just start happening or did someone work on the car recently?

If it turns out that the oil pressure is below specs and the oil pump is the cause, instead of replacing the oil pump you might want to rebuild it instead.

https://www.Thunderbirdforum.com/engine-oil-pump-rebuild-procedures/

doug7740
1955 Thunderbird Blue

 

[RichW]

The other (low probability) cause could be a partially plugged oil pickup screen. This is on the tube that sucks the oil from the pan into the oil pump. I would expect it to look like a bad oil pump with the gauge test.

Thanks Pink TBird, I'll check that screen

 

[RichW]

You have gotten some great advice from the people on this forum, so wait until you have the oil pressure gauge readings before you start talking about replacing the oil pump. Since you don’t have the actual oil pressure specifications, the following is from Roger Fuller, who is the 1955 Thunderbird Technical Editor for the Early Bird Magazine.


“The specs call for 45–50 lbs of pressure at 2,000 rpm with a hot engine. Some documentation I’ve read stated that the light does not come on until the pressure reaches 5-psi. However, when both the light and gauge are hooked up, my experience is that it will start to flicker at about 10-psi. Yes, it will go lower than 40-psi at hot idle. The lower the idle speed, the lower the pressure. Even hot summer days and hotter than normal running temperatures can thin out the oil. Anything that restricts the flow ends up in reduced pressure at the sending unit. It can happen from a blocked inlet screen in the oil pan or gummed up passageways within the engine. And yes, a weak or incorrectly repaired oil pump can cause the pressure to drop at idle as well.”


Check the obvious first:

• When was the last time you changed the oil and filter?
• Do you have sufficient oil in the engine and are you using the proper oil?
• Did this problem just start happening or did someone work on the car recently?

If it turns out that the oil pressure is below specs and the oil pump is the cause, instead of replacing the oil pump you might want to rebuild it instead.

https://www.Thunderbirdforum.com/engine-oil-pump-rebuild-procedures/

doug7740
1955 Thunderbird Blue

Thanks Doug, those figures will be good to work with when the test kit arrives.

 

[RichW]

Thanks Doug, those figures will be good to work with when the test kit arrives.

Guys, ran the car with the gauge and it started at 60 and dropped to 45 after about 25mins. Strange thing is that the bulb was still flickering even though the sender was disconnected, bad earth?

 

[doug7740]

No it is not a bad ground, as CSPIDY said; "The oil pressure light is looking for a ground to put the light on, you will want to check the wire from the light to the switch for shorts to ground".

doug7740
1955 Thunderbird Blue

 

[RichW]

No it is not a bad ground, as CSPIDY said; "The oil pressure light is looking for a ground to put the light on, you will want to check the wire from the light to the switch for shorts to ground".

doug7740
1955 Thunderbird Blue

Ok will do, thanks Doug.

 

[jbk-721]

don't know if I'm even in the right place to ask a question, will see I am a street rod guy, I just purchased a 56 T-bird have corrected some of the problems however, the oil light does not light up when I turn the ignition on. It will light come on when I ground the sender wire. Everything I have has a gauge on it. What do you think SENDER ?

 

[doug7740]

Since when you ground the sending unit wire the warning light illuminates, that tells me that the warning light bulb and the wiring are okay. It sounds like you have a defective sending unit.

doug7740
1955 Thunderbird Blue

 

[jbk-721]

thank you Doug, I'm a street rod guy, my cars have analog gauges. new experience for me. sure I'll be back with more questions.