My 90 renix has just shy of 223k on it and makes a bit more noise than I'm comfortable with. More so on a cold start and does quiet down a little after it's warmed up but, still sounds kinda like a diesel.
I tried some high mileage oil and it didn't do squat. In fact, I think it may be slightly more noisy now.

What is a good oil brand and weight to use that won't kill my mpg too much (only gets about 13 now) and doesn't cost an arm and a leg?

I considered getting the Shell Rotella T in 10w-30 but, there's also a T5 in that weight and I don't know which one is better suited for my engine.

 

20W50 and (or) "stop smoke" if piston noise
add ATF if lifters

 

Its piston slap.... run what ever oil you want the noise isn't going to go away. Save money for a new engine or a rebuild and drive it until you're not comfortable driving it any more or she blows.

For what its worth I run diesel 15/40 in my piston slapper.

 

I had some lifter tick. Especially cold. I used 10-30 and a quart of MMO and it's barely noticeable now

 

What is it u r wanting the oil to do? Basically, oil is a lubricant and coolant. Here's a little reading material for u (ok, a lot) that should dispel some oil myths that are soon to follow. Remember, flow = lubrication.

http://www.supramania.com/aehaas/

 

On my 90 I run:
5w30- 4 quarts (Quaker state or Penzoil)
1 bottle hyperlube (cheaper than LUCAS and been around longer)
1 bottle MMO helps kill the lifter tick
431,000 must be doing something right.

 

I've never used MMO in an engine. I use their air tool oil in my impact but, only because it's dirt cheap.

 

They make a product that can go in your crankcase or your fuel tank.

 

First off, what brand of oil filter is on the OP's Jeep?

 

^^^^^^^A+^^^^^^ Thicker oil kills your engine at cold temperature because of less flow.....and thicker oil ain't thick at 210 degrees!!!!!
So you are hurting yourself at cold start-up and at operating temperature you still end up with close to the same viscosity as a thin oil.

 

Wix 51626

 

It's not like I'm running 20w-50 in it. When I looked up what was recommended, it showed 60 F or above, 10w-30 and 0 F or above, 5w-30. I went with the 10 and I realize now that I should have gone with the 5. I may just re-do the oil change and use 5w-30 this time.

 

Not that big of a deal on the weight worth changing it. You've got a good filter on there.

Have you ever had the valve cover off? Or, taken a peek inside the oil filler hole to see if there's any build-up?

Just for giggles, here's something from the original owner's manual for your Jeep.

Jeep Engine Oil Viscosity
This was taken from pages 82 and 83 of the 1989 Chrysler/Jeep owners manual.
Selecting Engine Oil Viscosity
When changing or adding engine oil select the proper grade by using the chart on the following page. Select the grade that corresponds to the ambient temperature range you expect to encounter before your next oil change.
30*F to 100*F+ 20W-40 or 20W-50
0*F to 100*F+ 10W-30 or 10W-40
-20*F to 60*F 5W-30

 

im going to try this for my next oil change....5 quarts of oil, 1 quart of mmo and see

I have a very slight tick in the valvetrain...

do you run it for the 3k miles or do you drain it after 100 miles or so?

 

I run it til the next change. If you don't see an improvement after the first 1,000 miles, there's something else you can do to hurry things along.