I have a 2000 jeep grand cherokee limited. 6 cyl 4 liter engine. Yesterday the oil pressure gauge started reading high. Althe way up to 80 when cold, a little lower as it warms up. It is usually at about 45 I replaced the oil filter. No dif. Any suggestions? Will it hurt the engine?

You could start with the sending unit. Could be a wiring problem or it could actually have high oil pressure.
The sending unit is near the oil filter on the 6 cyl engine and I think on the 8 cyl too.

sounds like dirty oil clogged the oil pressure relief valve to me.
its stuck fast closed. bad deal that.
no engine option stated, so dont expect , accurate answers.

Normal oil pressure should be between 40 and 60 psi. A cold engine will normally have higher pressure. If you're seeing 75 psi on a warm engine I would recommend having the pressure checked with a manual gauge to verify the gauge in the Jeep is working correctly. If the gauge is correct oil viscosity may be too high (oil too thick) or there may be a problem with the oil pump pressure relief valve. If the gauge is not correct the sending unit may be at fault.

First off I wouldnt drive your car until you make sure that you have indeed oil pressure and that the gauge is a false reading, driving your car if in fact it has no oil pressure will severly damage your engine, but firstly i would check the oil pressure switch its located on the passenger side of the engine right back from the oil filter make sure the connector is clean and free from oil and corrosion if the connector appears to be in good shape take a paper clip and insert it between the 2 terminals inside the connector your oil pressure gauge should peak at 80 PSI that tells you that your gauge and all related wiring are good and in working condition, secondly remove the oil pressure switch and hook an manual oil pressure gauge up to you engine and start the engine the guage should have a oil pressure reading anywhere from 30 PSI to 55PSI depending on engine temperature if theres oil pressure on your manual gauge replace the oil pressure switch with a new unit, if you still have 0 PSI on your gauge then stop your engine immediatly and start looking at your oil pump and lubricating system for a problem.

the 1st thing that needs to be done is have a mechanical oil pressure test gauge hooked up to confirm the actual reading, the electronic gauge many times is incorrect.

the oil sending unit that screws in the block beside the oil filter may be faulty,
the worst thing would be the oil pump its self the regulator valve on it

sounds like an oil sending unit. about $ 50.00. I just had the same problem.

the 1st thing u do is have the oil pressure tested with a test mechanical gauge by a shop, most times it is just the oil pressure sending unit is defective, but never assume that is the problem, low oil pressure will distroy a $5000.00 engine very quickly, u can just try a new sending unit, but highly recommend a pressure test with a mechanical gauge before you run the engine anymore.

if the gauge starts a 0 - goes to 1/2 , than full - sounds like gauge is OK - seems to me like the sending unit is bad - you could try removing the sender and trying to clean out the port with "brake clean", letting it dry than re-installing it. the pressure switch is still the least expensive place to start

I think you have a bad ground on your engine gages...but, more importantly, have your oil pressure checked by a mechanic.  If it is indeed only 20 pounds the engine is sadly on it's last legs.
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