I bought my 71 with a swapped 460 in it, and lately I've been having difficulties with oil pressure where it would suddenly spike low.

So doing so I checked the oil naturally, but the previous owner had installed an after market short *** dipstick which he says apparently is made for the year 460. And it's reading on this real short stick, even so I added a quart just to see what would happen. Ran it for a little then...

I still was getting low pressure at times. Mainly when I was coming to a hault (I.e no gas). I pulled over for gas and she had taken abnormally long to crank over which concerned me, so maybe it really is low but the dipstick says otherwise??

I know she leaks a little it's just kinda hard to tell because I do have quite the power steering leak I need to take a look at lol (don't judge limited with time, resources and money.)

So basically my question is, what's going on here? Is it low oil, the gauge or pump?

 

Could be any of those, but it is very important to find out ASAP because low or no oil pressure is a motor killer.
Could also be the oil gauge sensor is bad or covered with 40 years of crud.
I would start there, clean it and if that makes no difference, then change it.
As for the dipstick issue, do some research and ascertain what your motor's oil capacity is with a new oil filter, then change the oil & filter putting in the correct amount and then you can check the accuracy of the dipstick.
If after those things you still get a very low reading, then it must be the gauge or the pump IMHO.

 

Are you using the stock OP gauge, or did you put in an aftermarket OP gauge? To check your stock gauge, ground the sender lead to see if the needle moves very far. If good, it should peg the needle. You might want to temporarily add an aftermarket gauge to see what your oil pressure actually is.

 

It's not uncommon for these trucks to read low oil pressure when at idle --especially for the low oil warning light to come on if you have an idiot light for the oil pressure, instead of an actual gauge. The low gauge reading (or warning light coming on, if it's an idiot light) could be legitimate --worn oil pump or excessive wear on crank bearings of the engine, etc.

On the other hand, the low readings may not be legitimate. It could simply be a matter that your instrument cluster ICVR (Instrument Cluster Voltage Regulator) is out of calibration. Other than taking the cluster loose to get to the ICVR, it's pretty simple to adjust.

This is the ICVR on the back of the instrument cluster and the adjustment screw that's on it.

The connections on your ICVR may be spade terminals instead of round, snap terminals but otherwise, the ICVR's configuration and function will be the same.


The ICVR adjustment requires two things: the fuel sending unit has to be working correctly and you have to have a full tank of gas. Turn the pulse adjustment screw until you reach the full reading of the fuel gauge. This will also bring up the voltage readings on your temperature gauge as well as the reading you get on your oil pressure gauge (or, if you have an idiot light on the oil pressure, it will most likely stop it from coming on and flickering when the engine is at idle).

This adjustement is for a stock instrument cluster with stock gauges or idiot lights.

 

Drain the oil, change oil and filter, put in 5 quarts and file a groove in the dipstick. Install a manual oil pressure gauge.

 

Wow, I never noticed the adjustment screw. What voltage should it be at 5.5V??