What weight and brand of oil are you using in your 4.2 with 120,000 + miles on it.

 

I'm only at 117,000 miles, but I plan on staying with 5W-30 Mobil 1 when I get to 120,000. Are you thinking about switching to a thicker oil?

 

Several brands have oil made for higher milage cars & trucks. Look for "High Mileage or Max Life" oil.

I read some where this oil helps with valve noise and can help oil pressure to.

 

I was thinking of switching to s full synthetic oil, but I've heard that you shouldn't switch to a synthetic if you have been running Dino for so long, bad for the seals or something like that. Any thoughts?

 

It should be ok to switch to synthetic up to about 75,000 miles. the reason they say not to change on an older engine is because the regular oil creates a carbon buildup around the piston rings, and thus creates a type of seal. If you replace it with synthetic, the synthetic will actually clean up all of that carbon and there will not be a seal, therefore causing it not to work properly. I switched to synthetic at 65,000, and I only have to change it every 10,000, works great. Also put synthetic in my rear diff and trans. Highly recommended by me.

 

The carbon buildup is like grit or sand and it will eat up the cyl. and rings. On high milage engines, 100,000 +, the crud can be cleaned out of the engine by use AutoRx for 1500 miles. Then safely switch to a syn. Under a 100,000 switch when ever u want to unless u have a really drity engine.
willb