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Mercury Mountaineer timing belt

I have a 2002 Mountaineer V6 AWDwith 151000 miles. I have a rattling noise when accelerating. I am told it is the timing belt or tensioner. My question is, is the V6 engine an interference engine where the engine is destroyed if the belt breaks? I know I have to get repaired at some point, but I also have a roaring noise in the rear end which might mean a differential problem. I need to prioritize the repairs. In fact, if someone has a suggested priority, I would love to hear what it would be.


This particular vehicles does not have a timing belt, is it possible that they meant timing chain or tensioner?

Sorry, I used the wrong term. It should be timing chain or tensioner. Thanks for the correction.

I personally would prioritize the timing chain repair over the rear differential. However, it’s also possible that the roaring noise in the rear could also be a wheel bearing which could become a safety issue. I would get the rear-end noise diagnosed first at least to determine what exactly you’re looking at before you make a decision.

Thanks for the input. Going in this morning for the rear end noise diagnosis. I was leaning in the order you suggested. It’s nice to get a second opinion that confirms my thought.

TSBs - Some 02 (99 - 02 ) Mountaineers With A 4.0 SOHC Engine Make A Timing Chain / Tensioner Noise,Usually Between 2400 - 2500 RPM

Paul, in second gear, accelerate from 2000 RPM through 3000 RPM and listen to verify this.

The fix is a Ford / Mercury kit (one kit for balance shaft engines and a different one for non-balance shaft engines) that includes an improved primary chain tensioner, chain guide, jackshaft and crankshaft sprockets, and includes an improved primary chain tensioner. It also comes with fasteners and gasket(s). It looks like the job typically calls for 6 to 7 hours of labor. This is all outlined in a Ford / Mercury TSB (Technical Service Bulletin).

As for the rear-end noise, another TSB (02 - 05 Mountaineers) covers replacing bearings / gears (kit) in the differential if proper daignosis of an axle whine or hum calls for that.

If you’re more fortunate, another 02 - 05 Mountaineer TSB dealing with a noise from a rear wheel hub bearing outlines a newer service procedure that makes possible a lower service level of the bearing / base part (?) to repair the condition causing the noise.

I strongly recommend that whoever works on this vehicle to consult applicable TSBs in order to properly diagnose the problems. It could save much time and money.


Thanks to all for your comments. They were most helpful in identifying a course of action.

Have you had the vehicle scanned for codes? I’m assuming here the engine is not rattling at idle or when revved while the vehicle is stationary?

If so, rattling on acceleration only while the vehicle is moving can point to a pre-ignition rattle and most of the time this is caused by an EGR system fault. Sometimes an EGR code(s) will exist and sometimes they do not even when there is an EGR problem.

Another less likely cause could be a rattling exhaust heat shield. I only mention these because things like this are frequently misdiagnosed and one should consider the simple stuff first.

As to the rear end noise, and assuming the fluid level is fine, this may be nothing more than a rear wheel bearing or even an irregular tire wear problem. I would assume again though that the tire tread has been considered.