Low Oil Pressure,Rebuild...

Are you going by the stock temp gauge or an aftermarket one? The stock ones are poop, but if you don't want to bother installing an aftermarket gauge, at least try swapping out the temperature sending unit (driver's-front area of the intake manifold). Costs less than $10, last I checked. Make sure to use Teflon tape on the threads.

Still running hot? Do a compression test - verify you have good numbers on all 8 cylinders and no low readings to two adjacent cylinders. That'll rule out a head gasket.

Check timing. Roll it back to 10* BTDC (stock) and see if that helps. No? 'Kay. Move on to the next item.

Check your fan clutch. Give it a spin while the engine's at operating temp (and shut off, obviously). It should be fairly stiff and not turn very easily by hand. If it spins freely, it's junk.

Is your air dam in place under the radiator? If not, hit up the junkyard and grab one, or just fabricate one - it's not high-tech, you can make one out of sheet metal or plastic garden edging if you need to.

None of that turn up anything? Buy a 180* thermostat, T-stat housing gasket, some radiator flush, and a couple of gallons of antifreeze. Run the Super Flush crap through there, drain, flush, swap out the T-stat, and refill.

Still overheating? Your radiator is FUBAR - cooling fins are covered with corrosion or the tubes are plugged with junk. Replace with the biggest damned radiator you can cram in there for a fair amount of money, and call it done.

If that doesn't work ... dunno. Call a priest, I guess, and have him perform an exorcism.

My car has a weird oil pressure problem. the needle likes to bounce around alot. 95% sure its the sending unit.

For your mileage issue.. PM your vin and ill run a carfax for you

The low oil pressure is still probably a consequence of the car running hot (oil loses viscosity as it heats up) and/or possibly a faulty oil pressure gauge sending unit. Really need to just spend a few bucks on a cheap gauge and mount it up under-hood just for testing purposes, if not a permanently-mounted one on the A-pillar or wherever you prefer it in/on the dash. Stock gauges are crap for getting true readings on much of anything. It would help to know exactly how many PSI you're getting for oil pressure before you go declaring your motor toast.

Ditto for the temp gauge - the stocker doesn't give a real reading in degrees, just those ballpark figures of "somewhere between this letter and that letter in the world "NORMAL" that could mean damn near anything. Aftermarket gauges aren't that expensive, unless you WANT a fancy and expensive gauge, and they're not hard at all to mount up. Less than $40 will get you an Autometer triple-gauge set (volt/water/oil) from most parts stores, and they're standard-sized so if you want to later on, you can buy a molded A-pillar mount or something and transfer the gauges into that.

If you're not using quality gauges to obtain reliable measurements, the temp and oil pressure data you're working with is suspect, at best. Get ACCURATE readings first and THEN you'll know where your engine's health stands in those two areas.

A possible reason that you're losing coolant but not really seeing it leak out anywhere is that your coolant overflow tank is probably cracked and that's why it will never stay full. I don't think I've ever seen a single one of those damned things that ever held more than a pint of coolant for longer than 24 hours before it drained out. They always seem to crack along the seams where the two halves of the tank were molded together. You're better off either fabricating one of your own - I've seen some pretty groovy overflow tanks made of Home Depot PVC pipe fittings that you can paint to look nice - or just buying one of those universal overflow tank kits and figuring out a way to mount it up underhood someplace (maybe behind the front bumper or in a fenderwell, if you're really crafty). The leaking overflow tank won't necessarily be causing your overheating problem(s), but if absolutely no other place underhood reveals a visible leak source, that would be the first item I would suspect.

Did you ever do a compression test on the motor to rule out a head gasket issue? (Significantly lower pressure readings in two adjacent cylinders usually indicates a failed head gasket.)

Have you checked the timing yet to verify that it's not over-advanced? (10* BTDC is stock, anything between 10 to 14* is usually pretty safe on most 5.0's.)

EDIT: It might help if this thread were in 5.0 Tech instead of 5.0 Talk.

My 91 has a bunch of miles on it and it starts out at 50psi cold, then drops to 30 psi at idle once it is warmed up (I'm running Autometers), it also gets really hot (as much as 220 with the A/C on while I'm idling), but my radiator needs replacing. Until you get some real gauges on it you won't know for sure. Also, you might try crawling under the car and looking at the bottom of the water pump, mine was doing that when I got it, and it was leaking coolant from the weep hole.

Makdaddymac said:

new waterpump so that aint it....

my radiator is probably the worst build up ever seen it def needs replacing but m fan was also bad...

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I just finished putting a new rad in my 91 today (Autozone special) and I went from running 205ish with the A/C off to 190. I need to get it out and run it to work on my daily grind, but it seems to cool a lot better. Funny thing is, the new rad was supposed to be a two core aluminum, but it actually is a single core with just one huge tube (looks to be a little over 1"), only down side is plastic tanks.

Makdaddymac said:

yeah thats cool. let me know. i was thinking about getting that one two cause its like 95 bucks but im craiglisting cause of the plastic tanks

ps. what was wrong with that 306? 14.16?wtf???

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That was my old car. I sold it a couple of years ago. The power band dropped off at 4800 rpm when it should have pulled to 5800ish (so you can imagine the problem that caused with 4.10's). I think the cats were clogged on it, but I didn't come to that conclusion until after I had gotten rid of it, so technically I'll never know.

Makdaddymac said:

hows the plastic radioator holding up?

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So far so good, it creeps up to 195 every once in a while, but falls back to 190 when I get moving again. Way better then the 220 I was seeing before. I was in my WRX all week, so I didn't really get to drive it out and about till today. It also has cooled down a little bit here in Texas, so its not quite an apples to apples comparison. A 25 degree difference is pretty big though.