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what's inside that oil pressure switch?

 
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Old 02 Dec 2017, 12:26 pm
RickinPA's Avatar
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Default what's inside that oil pressure switch?

I dissected a bad oil pressure switch to see what made it tick, here's the results.



The oil pressure switch is an assembly of parts, held together where the machined base is crimped over an insulating backshell to hold the guts together. I used a lathe to cut off the crimp, releasing the guts.

The rubber seal is a diecut piece that seals the machined base to a diaphragm.

The diaphragm appears to be made of Kapton (polyimide), a tough, high temperature resistant plastic film.

Behind the diaphragm is a short-stroke piston. It generally supports the diaphragm and only allows it to move a short distance, ~.040" (1mm).

All the above is captured by a ground contact. The ground contact is in electrical connection with the (grounded) machined base.

Mounted on the short-stroke piston is a metal washer that serves as a moving contact.

A spring is captured between the moving contact and the connector contact in the insulating backshell.

In Operation:

With no oil pressure, the spring presses the moving contact against the ground contact and the oil pressure light on the instrument cluster is lit.

When oil pressure develops, the diaphragm (working through the short-stroke piston) moves the moving contact away from the ground contact, and the oil pressure light goes out.

In Failure:

Oil leaks past the rubber seal and fills the cavity inside the insulated backshell. If the cavity is filled 100% with leaked oil, the diaphragm can't move beacuse the oil is non-compressible. That causes the contacts to stay closed and the oil pressure light to remain lit. It's kind of a fail-safe, you get an oil warning light when the pressure switch fails. The oil eventually leaks out of the backshell, making a mess on the engine beneath the oil pressure switch.

Installation Tip:

Oil pressure switches usually have a sealant, like Teflon tape, applied. The sealant leaves residue in the threaded hole in the engine block. It's not something you'd want floating around in the engine oil pressure galley.



Take a small diameter brush (make sure it has no loose bristles). Insert the brush into the oil pressure hole on the engine block. Press it against the side of the hole and orbit it in an unscrewing (counterclockwise) motion. You'll be surprised how much gunk comes out. I had to do mine more that a half dozen times before I got all the bits and pieces of Teflon tape out of the hole.
Attached Images
File Type: jpg oil pressure switch 4 with notes reduced.jpg (88.7 KB, 44 views)
File Type: jpg brush reduced.jpg (65.6 KB, 39 views)
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Old 04 Dec 2017, 01:46 pm
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Default Re: what's inside that oil pressure switch?

Great Job Rick
I wonder if it's possible to T-off the switch port so you could mount an analog sensor and get a true oil pressure reading while keeping the functionality of the on/off switch (probably required for the ECU to work). It looks like it's in the rear of the engine. Was it a pain to remove and is there room for more stuff?
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Old 04 Dec 2017, 03:02 pm
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Default Re: what's inside that oil pressure switch?

Quote:
Originally Posted by rsrocket1 View Post
Great Job Rick
I wonder if it's possible to T-off the switch port so you could mount an analog sensor and get a true oil pressure reading while keeping the functionality of the on/off switch (probably required for the ECU to work). It looks like it's in the rear of the engine. Was it a pain to remove and is there room for more stuff?
That switch was off a Neon, but the Cruiser uses the same switch. With the Neon access was from the top, fairly easy. I replaced the same switch on my Cruiser a couple of years ago. As I remember access was from underneath, it's on the back side of the engine towards the driver's side. I seem to remember I couldn't get a straight line-of-sight on the switch, but it wasn't too bad. If I remember correctly, the area around the switch was relatively clear. You need a special socket for the pressure switch.

There'd be no reason you couldn't T-off the port to have both the switch and a pressure gauge. I'd keep the pipe fittings short and stout, using a heavy wall pipe nipple (Schedule 80) if possible. You wouldn't want to have the weight of the switch on a length of pipe on a vibrating engine.
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