Odd Noise
 

I don't think this is a timing chain issue. I recently had the thermostat housing replaced and ever since it's been making this noise from 2000-2500 RPMs. It was only when it was cold but now does it all the time. It's driving me nuts. I've looked over the top of the motor but I didn't find anything loose. Can you guys help? Check out the video. The noise starts at 0:03 in the video.

Cold engine
Loosen belt tensioner and remove fan belt from crank
Start engine and see if it makes the rattle noise.
You can run cold engine for 2 minutes or so without water pump, Battery light will be on

If no rattle then noise if from one of the belt pulleys, spin each one, including the idler and tensioner pulleys.

If noise is still there then timing chain is most likely the problem, the new design for the chains and tensioners weren't installed until '05 model year, once upgraded they were not a problem.
The '97-'03 were a problem, '04 was the change over so hit and miss that year

Ok, I didn't think about pulling the belt. Brain fart on that one. I sure hope it's an accessory. Thanks Ron.

Belt pulled. Replaced both idler pulleys (they had some play). It did make the engine quieter but the noise I'm after did not go away.

I think it's weird that I can only hear it when the engine is under load. I can't hear anything out of the ordinary when it's sitting there idling.

Generally you would only hear timing chain rattle at start up, until oil pressure pushed out tensioners, and then at mid-RPMs

Good read here: Timing chain rattle resolution process - SOHC V6 - Ford Explorer and Ranger Forums "Serious Explorations"®

Explorers got the 4.0l SOHC engine in '97, Rangers got it in '01, so those forums have more early info on the problems.

Could the noise be Pinging/Knocking, which usually only happens under load?
Try running a tank of higher octane fuel, 91 or 93.

4.0l SOHC has 9.7:1 compression ratio so it WILL ping/knock on Regular gas, a Knock sensor is installed to change spark timing when knock is detected, if that is failing then you would get pinging/knocking under load with Regular gas.

Knock sensor is under the intake so under thermostat housing and it's wire comes out top front passenger side of valve cover and has a connection to main harness there
Picture of that connector here, post #9, lower left, yellow wire: http://www.explorerforum.com/forums/...d.php?t=351576
Those wires can get loose or frayed
Moving things around to get t-stat housing out and new one in could have weakened connection here.

Location of knock sensor seen here: http://www.explorerforum.com/forums/...d.php?t=353594
And here, 4.0l diagram: http://www.autozone.com/repairinfo/r...96b43f8036de4d

Thanks Ron. You are one helpful guy. I will give this all a read tonight when I'm not at work.

I did run a tank of premium through it 2 weeks ago to see if it went away. It did not.

I have some minor noise on start up. Maybe 50% of the time on cold starts.


I do have to pull the driver's side valve cover to replace it. The mechanic broke to the tabs that hold the PCV valve in place so now I've got it held in place with a bungee cord. Am I able to see the cassettes or guides that would be bad if that's the case? Maybe the link in the thread answers that.

Outside of something being obviously broke you wouldn't see much, engine has to come out to replace timing chains.

This thread has replacement procedure but look at post #16: SOHC V6 Timing Chain Parts Removal Procedure - Ford Explorer and Ranger Forums "Serious Explorations"®

I have read of people replacing this hydraulic tensioner and getting rid of a rattle, or found that it was loose, probably just temporary fix though.

I didn't think I'd be able to see anything. I might throw the hydraulic tensioners at it once it warms up a little. No garage and 10 degree weather make working on this thing a royal pain. Thanks again Ron.