No Oil flowing over valves when I look under oil cap

Started noticing the oil pressure being low lately. 30-40 in the morning when cold and 10 - 20ish when warm and 10-0 when at idle. Read about looking in the head with a light when its on so I just went out and started her up and she did her normal rattle at start up and the oil pressure gauge read 10 so I popped the oil cap and had a look in and didn't see any oil flowing or gathered at the bottom of the head so I turned it off and thought s%!t..
*oil is clean and not low
*its an 88" 6cyl 4.0l
Im thinking oil pump??? Any other thoughts or ideas?

1. What oil filter are you running? The Orange Can of Death--OCD--will give you a dry start up.

2. Put a mechanical oil pressure gauge on and confirm those readings--after changing filters if you have the OCD.

3. The oil pumps are not great in the 4.0, and the crank and rod bearing caps work loose and cause problems--the bearing caps should be re-torqued any time the pan is pulled.

4. NOT OFTEN, put the oil pickup tube can be loose where it enters the oil pump and cause problems--it is a press fit.

I had to pull the head off my 90 4.0 for a stupid mistake--I don't want to talk about it--and I put in new lifters as a couple of mine took a long time to pump up.

What do the rockers look like? Mine had so much baked on carbon and gunk on them it was hard to see if or how they were getting oiled. A Shop Vac and some pointy tools took care of that problem. I plugged up the holes that drain the oil from the head down to the galley with wads of paper towel.

As the motor gets older and the tolernaces in the bearings get larger the oil pressure drops.

Some people replace the oil pump with a high volume unit, some use a heavier oil, the connecting rod bearings are fairly easy to plasti gauge and replace if needed.

There is a pressure relief valve (labeled in some book I read) inside the oil pump. Mine was covered in solid varnish and carbon. I've often wondered if this was also a back flow valve?

I also took off the cover gasket for my oil pump, which seemed way to thick IMO and reassembled with a lite coat of permatex instead of the gasket. I did it at the same time as I replaced the connecting rod bearings, cleaned out the pump, screen and pan, went from 10-30 oil to 10-40 diesel motor oil and nearly doubled my oil pressure at idle. My success was likely a combination of things.

If your VC is leaking like most 4.0L. Removing the valve cover and run the engine with the VC off.

Rockers do look like they are pretty grimed up and the Valve cover is leaking so I will remove the cover and clean and inspect everything but for now I just replaced the oil filter so I'll see how the new filter effects the oil pressure next time I drive it.

Replacing the oil filter fixed the problem.. Got to love the simple fixes. Thanks for the help and advise

thanasi85 said:

Replacing the oil filter fixed the problem.. Got to love the simple fixes. Thanks for the help and advise

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OCD or another brand?

joe_peters said:

OCD or another brand?

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No shit. We've gotta know that!!

cruiser54 said:

No shit. We've gotta know that!!

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Definitely.

Sure would be nice to hear something...........

You had another thread on low oil pressure, and we advised change the filter. You never
responded to what you did. Now this thread. Everyone is glad to help someone who wants to be helped. What's up?