Engine Goofy Oil Pressure

Chad91gt

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Mar 2, 2017
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So my question is this . I have a1991 5.0. Has 106,000 no. Completely stock. My oil when cold and just started car is about middle of guage . Then as it warms up it goes down. Street driving is still pretty low. Around 1 to 2 notches above red. Then on freeway coasting is a lol highest and giving a little gas goes down a bit. Then when fully warm my needle sits on bottom on red or just above or below it on idle. Then bounces up a little bit then down . Was wondering if it is something internal. But thinking that the miles are low so maybe not. Or maybe it's a lol pressure sending unit. Any ideas?
 
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Elswick8400

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Apr 14, 2015
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Ive been here best bet i went to a store around here and bought a oil pressure test kit. Harbour freight dont know if u have one around u for ab $20. You need to hook up a mechanical gauge and check it. Its easy and best way to find out for sure. Stock gauges suck.
 

Chad91gt

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Mar 2, 2017
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So it seems pretty easy to replace the sender unit.. remove and replace? And does the oil pressure test kit simply hook up to the sender?
 

jrichker

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Another vote for replacing the the sender - less than $15 at any of the major auto parts stores.

Check to see it the sender is the problem - turn the ignition switch to Run, remove the wire from the sender and ground it to the engine block or battery ground. It should go to about 75% of full scale.
If it does not, then the problem is not likely to be the sender

If that does
 

Chad91gt

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Another vote for replacing the the sender - less than $15 at any of the major auto parts stores.

Check to see it the sender is the problem - turn the ignition switch to Run, remove the wire from the sender and ground it to the engine block or battery ground. It should go to about 75% of full scale.
If it does not, then the problem is not likely to be the sender

If that does
Is the sender unit and sensor the same thing? Where is it located
 

jrichker

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Is the sender unit and sensor the same thing? Where is it located
Yes.
It is down by the oil filter

5971586_bwd_s334_pri_larg.jpg


Advance Auto Parts
BWD Oil Pressure Gauge Switch
Product Application(s):
1989 Ford Mustang LX •With Gauge BWD Oil Pressure Gauge Switch
Part No. S334 1989 Ford Mustang LX •With Gauge $12.99
 

Chad91gt

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Awesome. Thanks for the help. I can just remove and replace right? Don't have to worry about draining the oil?
 

jrichker

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Just twist it out and shout; nothing else to do ...

Unless you are foolish enough to try and do it with the engine running :lol:
 

Chad91gt

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9/16" open end. There may be some limits on how far you can turn the wrench in single pass, but just keep at it.
Hey man. Thanks for the help. I installed the pressure gauge switch and that did the trick. Never went below second white line on gauge when fully warm.
 
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