FogRunner

After being unhappy with idling pressure of 8-10 PSI on my 3.4 with 230K miles I decided to try a slightly heaver oil.

So I got a case of Mobile One 5W-40 synthetic oil and changed the oil and filter and the results look good. Hot idle is around 17-20 PSI and 55PSI at 3000 RPM hot.

After 500 miles I haven't noticed any lower fuel milage and the engine does seem to idle quieter (probably just like a clean car driving better than a dirty one LOL).

I've known several 3.4 owners that have ran 5W-40/15W-40 Rotella or Delvac in their engines for well over 200K miles with ZERO issues so I'm not worried about it being non factory spec oil.

Also the 5W-40 is a diesel oil but it also has the highest certifications for gasoline engine service too, it was designed as a mixed fleet oil. One advantage is it still has ZDDP (zinc) which is a great anti-wear additive. Vehicles with roller rockers don't need ZDDP but ones with cam shaft riding on a flat lifter like the 3.4 do and can benefit from the ZDDP.

Due to emissions the government made them take out of normal gasoline engine oil but still allows it in diesel oil.

And no I don't own any stock in Exxon/Mobile corp