New to me Ford 4.0 has low oil pressure at idle once warmed up

Joined
Jul 8, 2021
Messages
248
Location
SoCal
2005 Mustang, around 215k miles. I just got the car, saw the oil pressure light come on while driving home and just assumed an oil change would work (found out last service shop threw on the wrong size oil filter). Did the oil change, and still has that same problem. I'm not your typical BITOG forum user that thinks thicker is better, but should I go to 0w40/5w40 or 10w30 to help raise oil pressure? I don't know if it's going to be an oil pressure sender issue, or "engine's on the way out" issue

There is minor mechanical whine that goes away as the car warms up, can't confirm if that is coming from the engine's timing chain tensioner area, transmission (also on the way out, 5r55 is slipping in reverse but perfect shifting in drive), or the power steering system.
 
Joined
Jan 22, 2011
Messages
7,870
I would connect an actual gauge to measure the oil pressure. Idiot lights cannot be trusted. I would first suspect a bad oil pressure switch on the engine before having low pressure. They are cheap, easy to change.Try that before anything. I have had them go bad before.

If the pressure falls that low, usually the engine will get noisy and clanky sounding.

Heavier oil isn't the answer, it won't raise it much .
 
Last edited:
Joined
Jul 3, 2005
Messages
37,774
Location
NY
It could very well be a tired engine with those miles, or the oil pressure switch. As mentioned get an actual oil pressure reading from a mechanical oil pressure gauge. I prefer to check it with fresh oil and a new filter, or oil that is not nearing an oil change. Post the results. Those factory oil pressure gauges can leave a lot to the imagination.
 
Joined
Aug 23, 2020
Messages
674
Location
Canada
I'd start with the pressure sensor, unplug and clean the connection and plug it back in and see if that works.
After that replace it, they are $10-$25 and easy to change, after that I would try some thick 5w30 over the 5w20. But it could be a blocked oil pick up and/or worn out pump. You may be looking at dropping the oil pan and putting in a High Volume pump (to make up for engine wear) and cleaning the pick up.
 
Joined
May 21, 2018
Messages
3,365
Location
South Carolina
I'd start with the pressure sensor, unplug and clean the connection and plug it back in and see if that works.
After that replace it, they are $10-$25 and easy to change, after that I would try some thick 5w30 over the 5w20. But it could be a blocked oil pick up and/or worn out pump. You may be looking at dropping the oil pan and putting in a High Volume pump (to make up for engine wear) and cleaning the pick up.
As long as the pan is down pull a rod and main bearing cap, or two, and check the condition of the bearings. I wouldn't bother with the HV oil pump but if the bearings are bad enough I would replace the pump with a stock unit.
 
Joined
May 21, 2018
Messages
3,365
Location
South Carolina
There is minor mechanical whine that goes away as the car warms up, can't confirm if that is coming from the engine's timing chain tensioner area, transmission (also on the way out, 5r55 is slipping in reverse but perfect shifting in drive), or the power steering system.
The whine is probably the power steering pump. Ford's are notorious for this. Try changing the PS pump oil and use Mercon ATF ONLY.
Try changing the transmission fluid and filter with Mercon V ATF. It's probably never been changed.
 
Joined
Jul 11, 2014
Messages
3,399
Location
Paradise of Florida
Oil seems easier than the tearing into engine options. Socal? guessing warm weather so using the 5w40 or 5w50 already mentioned is an easy choice.

Did you cut open your old filter? What do you mean wrong sized filter? What size was installed and what did you use as its replacement?

Inspect for sludge. At your next oil change interval, might need to drain the oil, run the borescope/camera thru the oil drain, and view the oil pump pickup. Might even want to look under the valve covers too. Can wait 3000 miles for the next oil change interval for scope inspection and filter autopsy. No point in wasting the currect fill. Monitor for oil consumption. If any, top off with synthetic 15w50 or 20w50.

What can be done now easily is to add a pint bottle of STP synthetic. It'll bump the visc a little and detergents can help with some cleaning.

Time for ATF flush, PSF flush, and an ATF filter change. Hopefully fresh fluid might mask that whine a little. Don't forget about the coolant, thermostat, differential, air filter, fuel filter, serpentine belts...... all is probably overdue.
 
Top