Clogged Oil Filter or OP Sending Unit?

[Phishin]

Ever since Clevy told me my oil filter was plugged in these pics, I've been thinking....
Engine Guard II Filter

Bought truck with 160k on it. Engine was fairly sludged up from inoperable PCV system due to a clog in throttle body. That was all fixed a few days after I bought the truck. This old 350 has gotten multiple doses of Kreen and MMO.

Sometimes my oil pressure gauge on the dash drops REAL suddently from 30psi (which is my normal reading when fully warmed up) to 3-5psi. It will stay there for a few seconds, and then come SKYROCKETING back. The gauge FLIES from 3-5 psi to like 50-60psi (it's a sudden, quick rise on the gauge), and the gauge swings back and forth from 15-50psi for a few times until it settles around 30psi.

Is this what a gauge normally does when the oil pressure sending unit is going out or am I experiencing a clogged oil filter (OP drops to near zero) and engine oil bypassing the filter (when internal bypass valve opens in engine, OP quickly raises)?

I have tore apart my last few oil filters when I did an oil change, and they were fairly dirty (I'm stilling getting gunk out of the engine, with the help of Marvel's Mystery Oil) from the previous owner. I'm not sure if they were clogged or not though...

So, I don't know if the gunk/sludge is screwing with my oil pressure sending unit or if the filters are clogging on me and I really am loosing oil pressure temporarily while I'm driving. Sometimes the oil pressure gauge reads near zero for a few seconds, and sometimes it will stay there for a minute.

It seems like if the filter was clogging up, the OP would slowly drop. But on my gauge, the bottom just drops out of it. So, that's why I think it's the sending unit.

Thank you for your input in advance.

 

[danthaman1980]

Oil pressure sending units can go bad - mine went out 2 years ago, and the truck was only 8 years old at the time.

Replace the sending unit before proceeding with more difficult or expensive repairs or guesses.

 

[RF Overlord]

If I understand oil filter operation correctly, the filter media is a very small part of the total restriction in the oiling system, so you shouldn't see any change in OP whether the bypass is open or closed.

Sounds like you have a bad OP sender or a problem with the wiring from it to the gauge unit.

 

[toneydoc]

I have replace the oil pressure sending unit in my Jeep 3 times in its life. It jumped around like you are describing. Mine is fairly easy to replace. Hope that is all that is wrong with the truck

 

[zanzabar]

I don't see how the oil filter could intermittently go from clogged and thus triggering the bypass valve to open, to unclogged and working properly, and then back again. If the filter was gunked up it would be a much more consistent flow or no-flow scenario. Must be the sender or perhaps there are large chunks that get pressed into small places and do not allow flow until the pressure builds up to a certain amount (50-60psi?).

 

[Phishin]

Thanks fellas.

I've always felt it was the sender unit, but just wanted to make sure.

The unit is fairly easy to replace on my truck. All I really need to do is remove the distributor...maybe just the cap. No biggie. But what's kept me from doing it is the plumbing that feeds the sending unit. There are a lot of nightmare stories of guys snapping the cheap metal tubing when they try to loosen the threads to remove the OP sending unit.

Supposedly the truck won't start or run without sufficient OP, but mine has never dropped to zero....just real close to it.

 

[Jim Spahr]

Both the oil filter and the oil pressure sending unit are relatively cheap and easy to replace, compared to the consequences of running an engine with low oil pressure. If you are treating your engine for sludge and have chunks of sludge floating around in the oil system, you should be worried about other vital items getting choked up with sludge. For example, the oil pump screen, the oil pressure release valve, NOT just the oil pressure sending unit...... I would change the oil and filter, and the oil pressure sending unit. Then see how the oil pressure reads.