On the way home last night I noticed I had low oil pressure on my 70 F-350. the needle was the whole way over to the left. The engine was not knocking or sounding like it was low on oil, however.

I wasn't too concerned because I had my instrument panel out to replace two light bulbs earlier in the day. I just checked my oil level and it is right on the mark.

So, is it possible I knocked off the sending wire at the back of the instrument panel or is my sending unit bad? Am I right to believe that if I am not low on oil my oil pressure should be good?

I can't say for certain that the gauge was showing oil pressure before last night. I was focused on the gauges last night since it was the first time I had all the dash lights working...

Advice please.

 

These motors will live with minimal oil pressure, but not for long.

I'm betting the gauge is okay, as it is wired through the plastic printed circuit on the back of the cluster. Only real connection is the plug that hooks everything up.

If the needles moves at all when you start it, then I would start with a new sending unit. Might be a good time to buy a cheapo mechanical gauge and do a quick install to see what it actually reads.

Oil pressure is made by two things: oil pump that produces the flow and the restriction in the bearings that create the pressure. If the bearing clearances(like the crank/rods) is worn the pressure will drop as you loose the restriction, thus loose pressure.

Typically it won't just go from OK to nothing unless something catastrophic happens. Say the oil pump locks up(and breaks the driveshaft from the distributor). It won't run long before it lets you know it is not getting any oil.

If you are getting even 10-20# of oil pressure, it will survive if driven easy at low rpm. My first truck(70 F100) with a 302 in it, it was whipped. The mechanical gauge took like 5 seconds to even get a reading of 5# on it when started. It ran that way for over a year.

 

I would check this out ASAP. My old oil pump never
moved the guage past the one quarter position and my new one moves it to the half way point. Low or no oil pressure is a motor killer.

 

The needle on the gauge does not move at all when I start the truck. The needle just sits the whole way to the left.

 

I would buy a cheap mechanical gauge and see what you actually have. Then based on those results, either get a new sending unit, keep the mechanical gauge , get A new oil pump, or all three...

 

I'd look for a bad connection , you said you were just behind dash changing bulbs , probably knocked a connection loose

 

If it was working before, then recheck connections. If not follow the advise from 351clevelandc4

 

Yes, as above, by all means resolve the situation. For $25 you can get a mechanical gauge with all the adapter fittings you need to get in the block.
If you don't want to spend the money, there is a Toothless Jake test for oil pressure that will only cost you the price of a quart of oil:

Crawl under, remove the oil filter, have wifey fire it and immediately shut ot off. Either oil will blow all over you or not. You will know if you have oil pressure.

Semper Fi

 

Thanks guys. I will not drive it until I solve the problem. First I will remove the cluster and check the connection. Then I will check the connection at the sending unit. If that doesn't solve it then I will buy a mechanical gauge.

I am new to these newer trucks.... Ha ha...... Where is the sending unit located on the engine block?

 

Couldn't you just ground out the connector at the sending unit to prove that wiring is good?

Once you ground out the connector the oil gauge should go High fairly rapidly.

 

the sending unit is a pill bottle sized item just above the oil filter housing with one wire on it.

 

+1 GROUND IT should max out the Gauge .

 

Newer?!?!? I consider my Ranger old-school, my F-100 is pre-historic.

 

Abe is still in the late 40s era haha. Bumps are high tech!

 

I'd put a Tee just below the oil sending unit to install a manual gauge.
Use some Teflon tape so it won't leak.
You may have to buy a few extra brass fittings to make the hook up.
Many brass fitting come with a gauge.
Orich