Which Mitsu 4-cylinder are you talking about, blmqzjc?
My wife has a 2001 Eclipse GS 5-speed with the 2.4 SOHC 4 cyl. 170,000 miles on it, had a previous owner (she got it at 130k miles) who did not check/change the oil regularly.
The dipstick was severely varnished at first. We went 20k miles on Castrol GTX 10W-30 at 3k mile OCIs. That oil got black fast. Was doing some serious cleaning. Then we went to GC 0W-30 for 2x OCI's of 6000 miles. Now we run RTS 5W-40 in it for 6k mile OCI's. The dipstick where the oil reads is 90% cleaner now than when she first got it, so I know the inside of the engine is looking better. The RTS cleans very well from how fast I've seen the oil change in a couple of our vehicles compared to other oils.
Anyways, point being, this 2.4 SOHC has 170,000 miles on it and runs like a dream. Oil consumption has been going down and down (duh, especially after fixing the valve cover gasket). Uses a quart every 2000-2500 miles. Used to be 1000-1200 miles it would use a quart. I think things are cleaning up inside of it, rubber is being reconditioned, and this engine has a long life ahead of it. I just put a new fill of RTS 5W-40 in it (had 6500 miles on the previous fill of RTS) and with 700 miles into this OCI, the oil hasn't budged a hair on the dipstick that I can tell. The engine is actually getting BETTER with simple maintenance.