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