High Oil Pressure But No Oil???

Car: 1972 Datsun 240z
Problem: High Oil Pressure

When i turn the car to the on position, the oil pressure gauge sweeps just below 90 psi (the top of my guage). It used to be even higher than that but recently came down a bit. What really confuses me is that I just drained every drop of oil from the motor. How is it reading that there is ANY oil pressure, let alone HIGH oil pressure?

And yes, the oil was blacker than black (also supposedly had Seafoam in it at one point to clean the motor).

Is it my oil pressure relief valve?
Any suggestions?

 

[obi_waynne]

I'd check for a blockage in the oil lines. Did you use an engine flush? If it is that bad then i'd run some flushing stuff through it and repeat the drain.

 

[PKnFR]

No flushing. What exactly is a "flushing" product i can use?
And how exactly would i go about checking the lines?

 

[PKnFR]

Just read an article that just told me flushing my motor may be very bad.
http://www.nbclosangeles.com/news/local-beat/flushservices.html

 

[obi_waynne]

It's different stuff to this. The flush i'm talking about you put in with the oil "egnine oil flush". Most good auto stores sell it. It's like a detergent that breaks down the oil and makes it run out of the engine it should help de clog the rest of the car.

 

[PKnFR]

Wouldnt that be the same as Seafoam? I know that was added to the old oil and caused carbon deposits to billow from the exhaust and coat the rear with carbon (such a pain to wash off).

 

[picassoonwheels]

Ok, so here’s my 2 bits’ worth:

Firstly I feel there is digression here.

The pressing issue at hand is the Oil Pressure Gauge, and not the engine flush, where whatever damage could be done is done already.

Hence lets look into that first and tackle the other hindrance later, if you please…………?

This said, I would like to state;

Along with what the motor gurus have to say here, you may even want to consider this.

It could be that the gauge has just shorted out, and bypassed the internal circuit and thus is showing the maximum pressure at all times.

After all if you have just turned on the switch but the engine is not rotating, where is that pressure coming from......?

The Oil Pressure Gauge works on a simple principle of displaying the pressure exerted on a membrane or a small piston which moves in and out, relative to the pressure exerted on it.

The moving in is relative to the amount of pressure exerted on the membrane/piston, while the moving out is relative to the back pressure exerted on it, created by either a spring,( could be a coil spring, or shaped like the spring you find in wind-up watches or clocks, a clock-spring), or a pocket of air (like in a barometer).

So now, if your meter reads maximum, even in the absence of any oil, the most logical suspect here, is this spring or membrane, because there is no back pressure being exerted here.

Hence it would serve you well, to mebbe put in a temporary oil gauge and see if the readings come back to normal.

And if they do, Voila! Change the Gauge and you ready to go.

Now as far as engine flushes go, I have the opinion that putting a foreign liquid in the engine oil jacket is similar to draining your blood out and filling the blood-stream with alcohol. It would give you a hell of a kick, initially, but imagine what would happen over any prolonged length of time.........

Also I have a phobia for running my engine dry.

Thus my method of oil change is;

So I usually do my morning chores in the car, keeping the engine running as far as possible. This usually thins down the oil to an acceptable level.

I then drain the oil, and replacing the filter, top up again.

This practically removes all the gunk possible in the oil jacket.

Now depending upon the condition of the oil that has been drained, if it is too dark or depleted, I filter it thru’ fine muslin cloth, add some fresh oil, of half the viscosity and top put it back into the engine, where I even go to the extent of overfilling, using the old filter of course.

I then procede to turn on the engine and let it idle for 5-7 minutes.

I then drain it out, and patiently wait for atleast 30 minutes, before I install the new filter and fill up with fresh oil.

Never had a break-down due to oil, if that is any comfort to you.
Hope this helps.

Cheers

 

[Massive]

we used Forte at the garage to flush the engine

 

[Richard1]

Definitely suspect the gauge or sender.

your filter through the cloth won't do anything but add fiber to the oil and probably dirt. The filter normally will take out about 50% of anything below 20 microns (a human hair is about 75 microns), and 99% of anything 40 microns (half of the diameter of the hair).

2 options if you want to clean... a solvent product that works slowly over 1000 miles or so, or a good CI-4 diesel formulation, for a cycle, of a thinner grade for a period where you won't exert much stress, fast acceleration, etc.

I once had to change an oil where the drain plug had an inch of crud. looked like a cork. I put CI-4 SAE 10W-30 in it and told the owner to come back as soon as it thickened up. that was 2 days. The next was 2 or 3 days, etc. after about 4 changes, we went to a 20W-50 that the engine needed (more for accumulated wear).