oil pressure gauge problem

[RuralRoute C-30]

(Originally posted in the wrong forum)

So the '85' C-30 got front and rear seals replaced along with the oil pan gasket and timing chain(old one was loose) and cover, and now, the oil gauge reads as if the motor was on when its not. Even when the ignition is on it doesn't move. Coincidence or maybe a bad sending unit appeared? Was a ground I didn't notice get touched in the process?

No leaks around the sending unit.

Is there a way to test to see if it is the gauge or the sending unit? Dare I ground the wire from the sending unit and expect what, if anything to change? It is a one wire sending unit.

Beats me how one fix leads to another, and nothing near the sending unit was touched, but hey, it is an old truck and I am an old man which makes me quite familar with getting fixed in time for something else to break down!

Any suggestions is appreciated as "I do not know", bad sending unit, ground, gauge?.
Thanks,
Mark

[Restrorob]

Go ahead and ground the sending unit wire, The gauge should peg to the highest pressure when the key is turned on. If it does replace the sending unit. If it doesn't check fuses first then for power to the gauge, If you have power to the gauge check for continuity in the sending unit wire from the unit to the gauge. Could be a broken internal wire.

[RuralRoute C-30]

Thanks! What you said makes perfect sense. Now if I can apply it in the morning to isolate the problem.

Seriously, it helps a lot and glad to have a plan tomorrow on this topic. Just having to return to thinking mechanically after a few years away from 'old iron'.

It reminds me I have gotta buy that repair manual soon!

Appreciate the knowledge always,
Mark

[TheSleeper]

i had similiar issue and i finally took the gauge out, laid it on the battery, ran a hot and ground jumper, and then a jumper to sending unit, started truck, and found that the gauge and sending unit worked fine. sorta easy test for the sender and gauge if you have gauge out anyway. unfortunately i cant remember which posts were which off top of my head, i had a little diagram, which of course i probably tossed in the trash.

in my case, somehow i lost power to that socket only in the dashboard, as well as sending unit socket for oil pressure. i had to jumper a hot wire from the key on hot of my temp gauge below it, ground it, and run a new wire from sender to the other post on the gauge. I put it back in stock location and the oil pressure gauge has worked ever since.

[RuralRoute C-30]

Thanks for that advice. I did go out to my shop last night (beats watching television when I have a task on my mind) and discovered the fuses are all good and the wire to the switch has power when the key is on. Gauge is pegged to where it ordinarily would read at this time with no key on.

Plan to go to the local parts house this morning for the sender to go that route first.

Doing my best to not complicate the simple. A learning curve for me as that is one thing I am good at. Just getting to "know" this new "old" truck!

Always appreciate learning from those who "have been there, done that'.

Obviously I have bought into another "hobby"!

Mark

[RuralRoute C-30]

Well the trip to Autozone was educational. Apparently the oil sender this truck came with is for a 'light'. The 'gauge' sender, $19.99 at Autozone) will require some plumbing for clearance from the distributor.
Old vs. New:


Now remember, this is a 'new' used truck that already I've confirmed is not with the original motor. Yet I still recall looking at the gauge when I bought it and I swear the gauge moved...? Oh well, at this time I just want to make it right even if I am wrong and have an oem electrical oil gauge working. So should I just plan on plumbing what is supposed to be the correct oil sender for a 'gauge' and then see what happens? (parts stores didn't carry the plumbing parts but there is no way that gauge sender will fit without being raised a couple of inches and relocation away from the distributor)

I did go ahead and install a new $7 sender, the same as the one I pulled out, just to try it. Nothing changed.

Here it gets interesting as I decided to go ahead and pull the gauge cluster. Only two lights were working anyway and why not take a look at behind the gauges? This day was already going 'south'!

The pics tell the story of what I discovered:
Any input is welcome. Looks like one project has led into another and so it goes. Yet it is better to do this now than when I need this truck. Also this truck was known to have sat for at least 12 months until the guy I bought it from bought it from the original owner last August. (I've had it for a month)

I do notice a lot of corrosion behind the oil gauge as seen in the pictures.






Since I have gone this far I want to focus on both getting the oil gauge working properly as well as what is needed to clean this mess up. No point not to imo.

Question: Is the back half of this gauge cluster worth cleaning up with the corrosion around where the oil gauge is? Is it compromised with so much corrosion?

Any advice to clean this mess up? I figure while the dash is apart I can work on straightening out some of the wiring and sand and maybe spraybomb the sheetmetal behind the dash area.

Once again, appreciate the help. This just happens to be "one of those days" where one thing led into another.

Mark

[kikkegek]

interesting thread. I have an oil guage that moves to the 15psi as soon as I start the engine and then stays there all the time while revving from 700 - 3.000 rpm....so I need to check my guage and sender too....thanks for the advise at the beginning of this topic...