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Oil Pressure Switch for Fuel Cut-off

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gonzo

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Thinking of using an oil pressure switch to cut-off power to the fuel pump. To hook it all up I will need 3-way adaptor off the block with a 1/8 NPT female and two male fittings with appropriate thread to install into the block and attached the oil line for the OP gauge. To the existing oil line to block male adaptor appears to be 1/2 NFT or NPFT - fine thread or perhaps Whitworth. Does anyone know for sure what thread is used for AH 3000 oil line to block? Suggestions? Thanks
 
I don't have an answer to the fitting in the block thread size because I installed a pressure switch for my bright idiot light the easy way. I cut the line going to the gauge between the firewall and the gauge and installed a compression fitting T with a 1/8 npt male branch and an 1/8 npt female coupling for the pressure switch. One advantage is it's all accessible if the pressure switch fails - I used to have the tee and switch on the block but when a switch failed, I found out what nasty job it is to change a switch in that location in a fully assembled car, I made the move to under the dash.
Compression tee
 

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Perfect. That's an excellent solution that I'm going to copy for my purpose. I plan to use a Standard Part Oil Pressure Switch PS-064 with power cut-off between 7 and 11 psi. Thank you!
 
gonzo said:
Perfect. That's an excellent solution that I'm going to copy for my purpose. I plan to use a Standard Part Oil Pressure Switch PS-064 with power cut-off between 7 and 11 psi. Thank you!
Click to expand...
Be sure you have a bypass on the switch so you can fill the carbs and start the engine.
 
John Turney said:
Be sure you have a bypass on the switch so you can fill the carbs and start the engine.
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gonzo said:
Thinking of using an oil pressure switch to cut-off power to the fuel pump. To hook it all up I will need 3-way adaptor off the block with a 1/8 NPT female and two male fittings with appropriate thread to install into the block and attached the oil line for the OP gauge. To the existing oil line to block male adaptor appears to be 1/2 NFT or NPFT - fine thread or perhaps Whitworth. Does anyone know for sure what thread is used for AH 3000 oil line to block? Suggestions? Thanks
Click to expand...
Hi Gonzo--

I don't know how many seconds it would take for the engine to shut down after having first burned the fuel in the lines and bowls, but If your goal is to save the engine I don't think that would be immediate enough. Plus, as John points out, you're going to have to provide a method of bypassing the switch in order to refill the system in the event the engine does not start.

I'd opt for a simple red light big and bright enough to get your attention which is the setup I have in my 100 and both race cars.
 
As others have pointed out , waste of time as the engine will run until the fuel lines are dry etc . Here’s my dash set up with a large red LED off an OP switch mounted on my oil filter sandwich plate .
 

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Instead of trying to kill the fuel pump, you could tie it to the ignition; not that it doesn't come with its own set of problems...

If I were heck-bent on doing such a project, I'd use a time delay relay activated by the starter push button, to bypass the path across the pressure switch. After X-amount of time, the engine has started and closed the circuit via the pressure switch, and the path through the t/d relay has opened. A loss of oil pressure at this point would kill the engine.

Just to be on the safe side, I'd keep a (test) clip-lead or two in the car ;)
 
You could open circuit both the fuel pump wire and dizzy wire with an oil pressure switch.
That'd also prevent the engine firing up with zero oil pressure at the expense of a speedy start.
 
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