How many miles does your intrepid have? Your engine is probaly sludged up and the oil is not making it to the valves/lifters.

You relaly should try to remove the oil Pan and get the sludge out, but since you can't do the next best thing and cleanse the engine!

Today,  remove the regular oil and put in Mobil 1.

If you live in a cold climate use Mobil 1 10W-30, Multi-vehicle Formula,

http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil1_10W-30.asp

I a warmer climate Where the temparature does not go below 20deg  use http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil1_15W-50.asp

Change it ASAP and do it every 1000 miles till engine is clean.  Hope it not too late!!Then you can go to 3000 mile changes.