Oil Gage Issue

[97RangerPete]

Hello folks. New here. Hopefully someone can help me out with this one.
97 Ranger, 4.0 4x4, new to me. 150k mi
Been eliminating lights on my dash. Down to my check Gage light for the oil Gage.
Gage comes "on" when the key is inserted and vehicle powered on (engine not running yet) then drops as soon as the engine starts and does not register pressure.

I have replaced the switch and observed oil leak out of the tree with the switch removed (oil is getting to the switch). I have noticed the boot on the switch wire is a loose fit on the switch itself.

I have just changed the oil and filter (issue was present before) nothing off about the old oil that came out. I have driven the truck a hundred miles or so, no overheating, engine sounds fine, is being lubricated.

I will try to have someone monitor the gage while I am under the car fiddling the switch boot incase connectivity is causing the issue.

Thoughts?? Thanks and I appreciate it.

 

[RonD]

Welcome to TRS

Pull off the wire on the switch and use a jumper wire to Ground that wire
Turn on the key
Gauge should go up to 1/3-1/2, if so then wire and gauge are OK
If not then wire OR gauge has the problem

If wire and gauge work
Make sure Oil Switch has a good ground to the engine block, some people use "tape" on the threads and this means no GOOD ground
The switch Grounds the gauge when oil pressure is above 5psi(closed), and ungrounds it below 5psi(open)

 

[97RangerPete]

Welcome to TRS

Pull off the wire on the switch and use a jumper wire to Ground that wire
Turn on the key
Gauge should go up to 1/3-1/2, if so then wire and gauge are OK
If not then wire OR gauge has the problem

If wire and gauge work
Make sure Oil Switch has a good ground to the engine block, some people use "tape" on the threads and this means no GOOD ground
The switch Grounds the gauge when oil pressure is above 5psi(closed), and ungrounds it below 5psi(open)

Thanks Ron, good to be here and thank you for explaining that to me. Will test next time I'm at the truck. No tape on the threads, however, I remember seeing tape on the crusty tree to the actual engine block... Gave up trying to remove it for fear of damaging the block.

Suppose I can run a ground wire from the switch to a clean ground somewhere else.

 

[97RangerPete]

Well, the gauge registers when grounded with the engine on, so switch needs a better ground, will rig one up when I get a chance. Thanks Ron.

In other news, while poking around noticed that the "new" starter was hanging on by one bolt. P.O.'s mechanic must have "overlooked" the sheared off frozen upper bolt. So now I get to drill out the bolt... time to break out the beeswax.

 

[Dirtman]

I dunno if Ron mentioned this but its not a guage. Ford used a oil pressure switch (on or off) hooked to a guage. The guage simple reads halfway when switch is on. So there is no physical pressure information coming from the "sensor" it's really a switch. Just enough pressure to turn it on or not tells the guage to go to 1/2. So weird fluctuations are almost always ground issues not true oil pressure issues. Never ignore it, but realize it is what it is.

 

[racsan]

I had a similar issue a few years ago, my “oil pressure “ would fluctuate, turns out it was just alternator rpm causing a voltage change and thereby affecting the “guage”.

 

[97RangerPete]

Dirtman, yes I'm familiar with these switches, rigged one up one on my Norton Commando as a safety.
Been sidetracked with my starter issue. Pulled it off today, no way I'm getting the frozen, sheared stump of a bolt out of the top hole, ain't happening.
Drilled a new mount hole directly below the large mount hole for a new bolt. Will also explore JB welding a stud to the end of the broken bolt also... if clearance isn't an issue.

All of this rolling around on wet gravel in 35 degree weather.