i put a 1999 ford explore 5.0 motor in my 1992 mustang. It had good oil pressure at first but now it is at 10 psi at 2k rpm and at idle it is 5psi so what could be wrong

 

Mechanical gauge?

 

yes it is mechanical gauge reading

 

Sounds like someone put Lucas in to thicken the oil and get the pressure up for the sale. Now the viscosity is breaking down and the pressure is dropping. Best guess is a dead pump, but could be crank bearings as well. I'd call the seller of the engine.

 

i put a new oil pump in it and it still does the same

 

Let's straighten that statement out.

You ran the motor before installing the new oil pump, and you've verified that the readings are the same between both?

OR

You installed a new pump before running the motor and these are the only readings you've gotten.

If it's the former, you have issues in the oiling system beyond the pump. Clogged filter, crank bearing clearance too high, etc.

If it's the latter, it's anyone's guess, up to and including an installation problem.

 

Is it or is it not a fact that oil pumps usually work or don't work? I've never experienced a low pressure problem related to a new working pump. I would try changing the oil to a 5 20 and add a 1/2 qt of low viscosity additive and see if the pressure is higher at cold start.

Reasons like that is why I don't like to just throw someone elses motor in. I like a fresh motor when I change, even if it's just a stock rebuild or crate motor.

 

yes the reading are the same between both but the oil pressure was fine before that for a couple months then it started to do this have hardly any oil pressure

 

it has 5w50 oil in it and it comes up with these oil pressures ratings