1997 Ford Taurus oil pressure light comes on only when rpm's drop below 700. Have change the oil pressure switch but still happens.

First off,when did you last change the oil? Did you change the filter?
Sounds like an oil pressure drop,or a serious engine problem.
If the oil could stand changing,go with a heavier viscosity,like 10W30 or 10W40 if necessary.
ALWAYS change the filter when the oil is changed. don-ohio (:^)

this means a mechanical gauge test is required to check actual pressure warm idling if low below 20 psi then the oil pressure pump relief is stuck open or engine bearing are worn

If you want to know what it means, the warning light tells the driver the engine oil pressure is below 10psi.
You could be low on oil in the crankcase, it could be a faulty pressure switch, or something may have happened to the oil pump.

Oil light pops on at low rpm because at a low rpm, your engine is not running fast enough to maintain full pressure. this is because either you have an oil leak, or defective oil pressure switch.

Before you dig too deep into your purse check the oil pressure switch itself.

I have an oil pressure gauge that reads in analog, 0 to 150? something like that, any way, it moves like a tachometer, idle down around 10, revs up to 55, 60 when taking off and then settles down at 35 while cruising, I notice a change with heavier oil. Also, I know it will read 55 lbs pressure with 1 qt of oil in there, I tried it. So the pressure gauge has nothing to do with amount of oil in engine. As long as it is full, It should be ok, as long as it is reading pressure, but if the pressure drops off, shut it down and find out what happened, If it loses all the oil, the temp light should come on long before the oil light.

Measure your oil at normal operating temp, without the engine running of course. This will give you a more accurate reading once the oil has circulated in the system.

The system works like this:

• With the ignition on, the oil pressure indicator light on the dash should come on and flash. Once the engine is started, the light should go out and stay out as long as the engine is running.
• If the oil pressure drops below approximately 0.3 bar or 5 psi when the engine is running below 2000 rpm, the light will flash.
• If the oil pressure drops below approximately 1.8 bar or 27 psi when the engine is running above 2000 rpm for more than 3 seconds, the indicator light will flash and the buzzer will sound.

If either this two warnings occur:

• The engine should be switched off immediately and the oil level should be checked.
  

The check gauges light is normal because at 400 rpm it isn't running fast enough to build sufficient oil pressure. I am guessing maybe a vaccum leak???

Hello mb4494: My name is Roger and I will help you. If by changing the oil pressure sending unit the problem did not change. I would perform a oil pressure test. This is done by removing the oil pressure sensor and inserting a oil pressure gauge. This can be done by yourself or by a repair shop. This needs to be done on a cold engine. Start the engine and observe the oil pressure cold.as the engine warms up observe the pressure. The pressure will drop off as the engine warms up.Should the oil pressure drop below 10 to 12 PSI. then you have internal engine trouble. More then likely a bearing problem. Try dropping the truck into gear and see what the pressure drops off to. Again if the pressure drops below 10 to 12 PSI. you have a problem. I would also check to make sure you have the correct oil switch. a truck with a oil light uses a oil pressure switch. with a gauge you would use a oil pressure sending unit. Sorry for the long reply but want to make sure you check the pressure correctly. Please rate the quality of the answer as this is how we know the answer was correct. Thank You for using Fix Ya. Roger

how low does the oil pressure drop?? is it below 40?