Best Summer Weight Oil for High Mileage 1998 Explorer XLT?

[sjochssr]

Sorry to be so long-winded... but I have a question about whether or not to use a higher viscosity oil in my 1998 Explorer. The vehicle is a 1998 Explorer XLT 4.0L V6 SOHC VIN E. It has 466,000 miles on it. With my last kid in college, and going into her senior year this Fall... I really need to keep this thing running for one more year. I've only put 5W30 Mobil 1 Full Synthetic from day one. About two years ago, the vehicle started to "diesel" or make a rattling sound from the right front engine (driver's side). I'm familiar with the plastic cassette timing chain deterioration on the 4.0L SOHC, and guess it's likely the problem. I replaced the two front timing chain tensioners a couple of years ago but the ones I took off were in perfect shape. No issues. The rattling noise only really occurs after I drive it, stop for a few minutes, and then drive it again. On start-up after it's warm, the rattling is fairly loud. I've always been curious if the rattling could be something other than timing chains, such as maybe the vehicle needs new upper and lower manifold gaskets. I don't have any error codes though. And I'm getting ready to change the PCV valve. Anyway, does anyone have a recommendation whether I should bump the summer weight viscosity beyond Ford's specs to possible help with the (apparent) timing chain issue? I live in Northern Virginia. Hot (85+), & muggy from April through early October. Appreciate any thoughts or recs.

 

[BrooklynBay]

Welcome to this forum! I see that you've joined 8 years ago but this is your first post. Keep using the same oil if this worked for you to get it to almost 500K miles.

 

[CDW6212R]

10W-40 wouldn't hurt it, but the issue will need attention most likely before a year is up. The 4.0 external tensioners are fairly easy to replace, way better than the internal parts, and timing cassettes. I suggest doing at least those two parts, they don't cost that much, under $100(OEM) and the labor isn't too bad. It's not easy to find a synthetic 10W-40, but that's what I use in my 4.0 Explorer in Summer.

I have a similar noise from my 1995 4.6 SOHC Crown Vic, and have used a thicker oil since a rattle began years ago. That's a different engine and likely not the same issue, but thicker oil has alleviated the sound most of the time. I've tried to add some STP additives or occasionally etc.