I would at least try and drop oil pan and check pickup tube some say to do this as described below , but personally I would pull oil pan if possible and check pickup tube first hand ,,if clogged badly I would replace it an oil pump now before problem gets worse if it is the problem


How to flush
Oil pump pickup tubes are not easy to replace. The oil pan must be removed, and a new oil pump and pickup tube installed. Chances are very good that if the oil pressure has dropped due to a clogged pickup tube screen, the pump is damaged and should be replaced along with new crankshaft bearings as well. There is a procedure, though, that may help if the damage is not too severe.

Step 1

Drain the engine oil into a drain pan and remove the oil filter. Replace the drain plug and pour 1 gallon of Berryman B-12 Chemtool or a similar product into the engine oil fill. Do not crank the engine. Let the product sit in the oil pan for 2 days before draining.

Step 2

Drain the solvent out of the oil pan. Replace the drain plug and fill the oil pan with solvent once again. Allow it to sit for 2 additional days and drain the product. Inspect it as it flows out of the oil pan. If it is a dark sludge, the process will need to be repeated. Rub the discharge between two fingers and feel for carbon grit. If there is grit present, it will clog the screen. Repeat the process until there is no sludge or carbon grit in the discharge.

Step 3

Drain the flush agent one more time making sure it is free of sludge and carbon. Remove the oil fill cap and let the engine sit overnight with no drain plug or oil cap installed. This will allow the engine to air out.

Step 4

Install the oil drain plug, a new oil filter and add engine oil. Disconnect the engine computer fuse, or disable the engine so that it will not start. Crank the engine for 15 to 20 second intervals several times, allowing the starter to cool between each crank. This will prime the oil pump so the engine will not have a dry start.
Start the engine and pay close attention to the oil pressure. Listen carefully and make sure there are no engine knocks or rattles. If there is noise, the engine requires further repair.

Tip

• Remove the valve covers and inspect the valves and covers for sludge buildup. Normally this occurs when the oil screen is contaminated.

Warning

• Berryman B-12 Chemtool and similar products are very volatile and highly flammable. Use extreme caution while using these products. Do not use an engine flush that requires the vehicle to run. The engine bearings cannot endure this process.

 

What weight oil? What brand filter? Hopefully you didn't stray to far from the recommended. During your test drive before you got it was it ok?

 

As I understand it, you get the oil pressure light, but a mechanic gauge shows oil pressure within limits.
You could have an electrical problem.
When you replaced the oil, how many quarts did you put in? If you only needed 5 quarts to fill it then you may have a layer of sludge on the bottom of the oil pan. The oil pickup sits low in the oil pan and a layer of sludge will restrict flow.
Regardless, 72rtchallenger has good input on flushing your oil system. There are also other engine flush products out there that get good reviews.
I would have to get a look at the inside of the oil pan and the oil pickup screen. You could get a preview by using a borescope in your oil pan. Go in through the drain plug and look at screen and for a layer of sludge on the bottom.

 

5w-20 mobile one and mobile one filter. The oil gauge didn't work at all on test drive unless you turned engine off after cranking it and then cranked it back up. Further inspection revealed why. The sender wire looked like it had been cut and repaired but was pulled back apart. (not connected at all)

To answer other question, it did take more than 5 quarts to fill.

 

That engine calls for 5w30. Using a lower viscosity could be part of the problem. Engine oil capacity is 7 quarts, btw. I would swap your oil and see what happens. Also ask the PO what viscosity they used... could be the engine is looser than it should be and requires even more viscosity than 5w30.

Quick web search nets this:
"When oil viscosity is too low or high, it may be detected as a loss of pressure in the oil supply to the engine. Low viscosity generates less resistance to flow through the system, which is translated as lower pressure by the pressure gauge or sensor."

 

I didn't see anywhere where you stated the miles but a tired engine may need the 5w30 or even 10w40 high milage oil and still give you many years of life.

 

Just hit 102k

 

Not that many miles then. I would maybe try a light flush with marvel oil or what others have recommended then put the 5w30 in and go from there.Th 20w might be to light.

 

I really don't know how 5w-20 got stuck in my head. I remember when I bought the truck looking it up and thinking it was nice that is was 5w-30 as that's what my wife's Town & Country uses but I just went out to the shop and looked at the jug it cam in (poured the used oil back in it) and it is 5w-20.

 

If you know how many miles was on the used oil, you can have it lab tested to see what is floating around in there... I've done that for a few cars to get some insight to condition. I've used Blackstone in the past.