oil pressure goes to 0 and back

hey, Heres the situation I have a 88 xj that has about 235,000 kms on it, For the past 7 months the oil pressure will drop to 0 and it will make a fast ticking sound for like 5 seconds then return to normal , it only does this occasionly. Ive started putting 15-40 in it , but it doesnt really make much of a difference, . Also is it normal for the oil filter to be straight up and down ? Any insight would be greatly appreciated, thank you

The filter is supposed to be verticle in an 88.
Your oil pickup may be partially blocked, or the pump may be intermittantly stopping for some reason, or the distibutor gear may be damaged in some way.
I would guess it is not a sending unit issue since you are hearing the ticking when the pressure drops.
I would put some Seafoam in the oil and try to clean some of the gunk out of the oil passages.

when does it drop to zero? is it at idle or does it do do it after coming to a stop, or perharps while driving on the highway. This could be a couple of different thing give us some more info.

Thanks for replying, IT does usually happen when coming to or right after stopping. ON the highway its fine . Ive decided to build this one up , but want to make sure its worth it. Its got a few issues, this being the start.

I would pull the valve cover to make sure its not completely sludged up and the oil can properly drain back to pan. if thats not the case the spring in the oil pump is probably getting weak. Sounds like it can't maintain pressure at low rpms

I did notice a milky slime on my dipstick prior to my last oil change. I figured some water might be getting in from cooling system , even though my coolant looks normal, so i put some of that sealer stuff in there. Could that cause problems with the pressure? Having water mixed in?