oil pressure gauge

[blueyacht]

"1976 Merc. I/O 165HP Inline 6 GM motor"

First time motor has ever stalled on me. Looked down at gauges and oil pressure was jacked up to 80. Temp was a little high at 180. Tried starting a couple times and would only run for about half a minute. Went home and a day later ran it again OOW. Ran fine, temp fine, but oil pressure temp stayed at 80, in fact, it will shoot directly to 80 just in the accessory position before starting up. Through process of elimination, I thought it was the gauge. .....now, new gauge, new sending unit, and tempory sending wire and same thing.....gotta be electrical but just cant figure it out. Please help.

 

[04fxdwgi]

Re: oil pressure gauge

"1976 Merc. I/O 165HP Inline 6 GM motor"

First time motor has ever stalled on me. Looked down at gauges and oil pressure was jacked up to 80. Temp was a little high at 180. Tried starting a couple times and would only run for about half a minute. Went home and a day later ran it again OOW. Ran fine, temp fine, but oil pressure temp stayed at 80, in fact, it will shoot directly to 80 just in the accessory position before starting up. Through process of elimination, I thought it was the gauge. .....now, new gauge, new sending unit, and tempory sending wire and same thing.....gotta be electrical but just cant figure it out. Please help.

Gauge shooting high is an indication of a short somewhere in the wiring to the sender. Disconnect the "S" (sender) wire on the gauge and see what happens. Should go to zero....

Teleflex states the following conditions at sender for gauge readings :

Zero pressure = 240 ohms
1/2 gauge reading = 103 ohms​

full gauge pressure = 33 ohms.


Sooooo... High pressure reading = low resistance (short to ground.) You can download the entire gauge troubleshooting guide from Telflex site.

 

[Silvertip]

Re: oil pressure gauge

Chances are the wire on the sender has become shorted to the engine block somewhere in the engine bay. Of course it could have also been shorted anywhere along the line from the engine to the gauge.

 

[blueyacht]

Re: oil pressure gauge

when I stated temorary sending wire, I was stating that I ran a new wire from the guage to the sending unit. not sure how there could still be a short. Im gonna explore the grounding issue....perhaps thats why it stalled to begin with

 

[04fxdwgi]

Re: oil pressure gauge



A bad ground (high resistance) would cause the gauge to read low. I'm going to have to ask the obvious here.. Are you sure you wired the back of the gauge correctly?

1. If the gauge is wired correctly AND
2. The wire from the gauge "S" terminal to the sender is not grounded AND
3. The sender is the right one (not the low oil pressure alarm sender, which will make what you are seeing happen)

Then it should work.

Disconnect the wire from the "S" terminal on the gauge and see it goes to zero. If it does, with the seperate wire running to the sender, then I suspect you have a bad sender OR the sender for the low oil pressure alarm installed instead of the sender for the gauge. The alarm sender has zero resistance when there is no oil pressure and will show the gauge pegged out to max with engine off. Perhaps you inadvertantly picked the wrong sender to wire to or the parts guy sold you the wrong sender or a bad one from the box. Stranger things have happened.

One quick check... With engine off, disconnect wire at sender. Put your ohm meter across the sender terminal and ground. Reading should be high, around 240 ohms or greater. If it reads zero (or near zero) sender is bad or wrong one.