OIL PRESSURE gauge

[Greg]

I have always been a fan of 69 and 70 Shelbys but I never seemed to find "the one" until recently.  I purchased a really nice 70 that is a good car and it checked out (as far as not having a reported checkered past) by Vincent.   

The car was restored by in the 90's and the engine has about 1500 miles on it since it was rebuilt.  I took it out for about a 200 mile journey and it ran great.  There is however a concerning issue (Maybe) as I am driving the car.  When I start out, the oil pressure reads about 50psi on the gauge (original gauges).  I know the gauge is powered by a sending unit which are known for their inaccuracies but it is stable at idle and starting out.  After about 10 miles running at about 2800 RPM the oil pressure guage starts to go berserk.  It goes from 50 to 20 to 0 and bounces like crazy but when I decelerate it goes back to 50 and stays steady till I accelerate again.  The gauge finally goes to 0 and when I decelerate again it goes back to 50.   

First, I don't know anything about the engine (other than it is original to the car) as I didn't build it but it runs great with no weird noises, smoke etc... therefore I am thinking there are two possible scenarios.

1)  The sending unit diaphragm is weak and under a prolonged state it starts to fail.
2)  Someone put a high pressure oil pump in it and it is draining the pan causing the jittering needle under load (but that doesn't explain the positive 50 psi under deceleration

I am new to the 69/70's so I before I start my treasure hunt I figured I would see if anyone else has traveled this path.

Thank you in advance for your help!
Greg

 

[Bob Gaines]

I have always been a fan of 69 and 70 Shelbys but I never seemed to find "the one" until recently.  I purchased a really nice 70 that is a good car and it checked out (as far as not having a reported checkered past) by Vincent.   

The car was restored by in the 90's and the engine has about 1500 miles on it since it was rebuilt.  I took it out for about a 200 mile journey and it ran great.  There is however a concerning issue (Maybe) as I am driving the car.  When I start out, the oil pressure reads about 50psi on the gauge (original gauges).  I know the gauge is powered by a sending unit which are known for their inaccuracies but it is stable at idle and starting out.  After about 10 miles running at about 2800 RPM the oil pressure guage starts to go berserk.  It goes from 50 to 20 to 0 and bounces like crazy but when I decelerate it goes back to 50 and stays steady till I accelerate again.  The gauge finally goes to 0 and when I decelerate again it goes back to 50.   

First, I don't know anything about the engine (other than it is original to the car) as I didn't build it but it runs great with no weird noises, smoke etc... therefore I am thinking there are two possible scenarios.

1)  The sending unit diaphragm is weak and under a prolonged state it starts to fail.
2)  Someone put a high pressure oil pump in it and it is draining the pan causing the jittering needle under load (but that doesn't explain the positive 50 psi under deceleration

I am new to the 69/70's so I before I start my treasure hunt I figured I would see if anyone else has traveled this path.

Thank you in advance for your help!
Greg

It could be the sender. FYI it uses the Ford bell shaped sender and not the the can shaped SW one. It could be in the engine gauge feed harness. Sometimes they get brittle or damaged and you have a intermittent problem that may manifest itself with engine movement /vibration because the wire is broken inside the insulation.  The 69/70 oil pressure gauge itself is well known for going bad. 

[Greg]

Thank you Bob, the sender is the bell shape one, I haven't pulled it to see if it is a Ford part or not. I will probably run a secondary aftermarket direct pressure feed gauge just to make sure everything in fine as I chase the "jitter" :-). 

This is the first 428 SCJ car I have had and I will say, I am very impressed with the power especially with the drag pack 3:91 gears.  She pulls very hard, I'm very blessed to be able to be a caretaker of it.

[Bob Gaines]

Thank you Bob, the sender is the bell shape one, I haven't pulled it to see if it is a Ford part or not. I will probably run a secondary aftermarket direct pressure feed gauge just to make sure everything in fine as I chase the "jitter" :-). 

This is the first 428 SCJ car I have had and I will say, I am very impressed with the power especially with the drag pack 3:91 gears.  She pulls very hard, I'm very blessed to be able to be a caretaker of it.

The bell senders after market or otherwise will all work .Some will better then others. It is the more reliable item of the other 2 issues I mentioned. The assemblyline sender will have FOMOCO in block letters inside a rectangle.

[Shelbypat]

If the aftermarket reading is not better, I woul'd install a T behind sending unit and tape a mecanical gage on the windshield to compare on roadtest. 

Patrick

[Shelbypat]

And make sure the engine has a good ground.

Patrick

[Greg]

Thanks for everyones help.  It was the sending unit, the gauge is constant now and running great.