Low oil pressure when warm.

[RickD]

Hello all, I have a 2000 Ranger with the 4.0 ohv engine. Recently the needle on the oil pressure gauge has been jumping from the bottom of the gauge to the center, so following the advice on this board, I removed the oil sending unit, and installed a mechanical Stewart Warner gauge. When the engine is cold I have 50psi, but it slowly drops to 40 then thirty, etc., finally when it is warmed up and idling it settles to 12psi. If I rev the engine to 2000 rpm it will go to 25 psi, and if I rev to 3000 rpm it will climb to 40 psi. I am the original owner, and the truck has only 58,000 easy miles on it. Any ideas what I should do next? Pull the engine and replace the oil pump? Or could it be I need to try Seafoam first? Thanks in advance,
RickD.

 

[firefighter525]

Since you've already replaced your sending unit, check the gear on your Camshaft Synchronizer(it drives your oil pump). Its located top dead center of the motor back by the firewall. You'll need to mark it and pay attention to its alignment before removal. A new one will run you approx. $42.00 at rockauto.com and it even comes with the alignment tool. I can't really see the oil pump going bad at 58,000.

 

[Earl43P]

Those pressures look normal to me.
I MIGHT say look at your idle rpm, if it's less than spec, expect lower oil pressure.

The factory pressure switch is 8 psi, IIRC.

If it ain't broke, don't fix it.