couple different issues - all fairly simple
 

#1 - I replaced my oil pressure sending unit about 2-3 months ago with a mopar unit. Works great, until last night...i start my jeep (cold) and drive about 5 miles
That first 5 miles my jeep "had" 80lbs of oil pressure. Now after that...it went back down to normal oil pressure. Is my sending unit bad again? is there a warranty on mopar parts like this?

#2 - Heater core, i flush and flush this thing...every time it gets warmer, and junk comes out like crazy the first few "flushes"

Now it will be hot for a week or so...than slowly gets colder and colder....and then i flush again and we start all over.

My question is this "whats going on?" do i have this much crap in my system?
I have a mixture of about 60% water, 40% straight coolant....ideally i should be 50/50....but is this mixture affecting the heat?.

I know what jeep heat is like...right after a flush i have it...but it slowly fades away until i flush it again about a month later

suggestions for me?

Dirty radiator that keeps letting crap out of it and into the core?

Sounds like it. You probably need a thorough flush of the entire system.

I'm having the same problem as the OP with my core. Flush it and the heater works great for a week or two, then starts getting colder till it's just lukewarm air blowing. Flush it again and rust colored glop comes out, and it works great again. For awhile...

BUT... Here's the catch.

I have a newly remanufactured ATK longblock AND a new radiator (as of November 2011). The water pump got transplanted from the old block, but upon inspection it was good, didn't leak or have shaft play, and the fins were all in great shape. Based on that and the fact that it didn't even come close to overheating this past summer in weeks-long 110 degree Texas heat with the A/C on, I assume my circulation is good. I've had the heater issue since the engine/radiator swap.

Just not sure where these orange core turds are coming from.

Only thing I can figure is that perhaps there is some kind of weird chemistry going on and causing residue to build up over time. Or perhaps there is/was some kind of engine assembly lube/grease/sealant that has gotten in the system and coagulated.

well what i know is the previous owner wasnt very good with upkeep on the jeep

His wife drove it, i think she basically just put gas into it. always took it to the jiffy lube for oil changes

The jeep is in great shape...im just going back and doing the little things....I have no doubt in my mind the coolant is the original...

Im taking to a local buddy of mine (owns his own shop)
He says he has a machince, forces a cleaner in, lets it sit...then flushes it out with a vacuum assist pulling it out

I think personally from flushing in the past...i have build up in the motor, heater core and radiator....his machine should flush all three.

He did my truck a couple years ago.....that system was always cleaned..but he still ran his machine on it for about 30 min before it was coming out clean

I can only imagine whats in my 99 jeep...