Have an 03 Montero 3.8 and the other day it started making an awful noise. It's always had a small bit of lifter noise, but nothing like this. It does not go away after warm up like some noise reports, but it will seemingly get lighter after I go over about 2300 rpm. Any lower than that and at idle it is very noticeable. Here is a small recording of what I'm hearing.

https://www.dropbox.com/s/pbxrql7fxs...20001.m4a?dl=0

I just cleaned and checked all the valve adjusters after the noise appeared, so I'm pretty sure it isn't that. It has a little over 140k on the dial and I bought it with a little over 60k. I've not replaced the timing belt since I've owned it, and I'm not sure if it was changed before either.

 

That's an awful noise. Can you localize where it is coming from? Is it on top (one side or both), front of the engine or main block? In a way it does sound like a really bad case of valve slap, but also reminds me the noise that happens when timing belt tensioner fails.
My guess that the noise is coming from the front of the engine (more on the passenger side) and it is the timing belt tensioner.

 

It is coming mostly from the passenger side from what I can tell. It is loud enough though that it's difficult to pinpoint. How difficult would it be to diagnose the timing belt tensioner?

 

You need to take off the plastic covers on top of the cam gears on the front of the engine. I believe to get to that point you need to remove serpentine belt, cooling fan, accessory bracket (pretty much everything from the front of the engine). If you are able to take off these covers you can start the engine and you'll see the timing belt having too much slack and slapping around there hitting the things around. It is pretty much half way to doing the timing belt job all together. Now that you've confirmed the noise coming from passenger side and noise being very loud, I'm pretty sure it is the timing belt tensioner. You should go ahead and do the timing belt - 140k miles on most likely original belt is long way overdue. You will need new timing belt, timing belt tensioner and tensioner pulley. Some people like to replace the water pump and/or cam seals at the same time (you have to get down there for all these). Not sure if you are able to do this yourself or take it to the shop, but that is what you are dealing with.

 

I think Hunter is on the right track and certainly the Timing Belt needs attention if it has never been done. I did mine, the seals, water pump etc and considered it to be a intermediate challenge to a DIY wrencher. My Montero is a 3rd car so I just put it in the garage, took my time over a few days and gutted it out. The biggest PITA is the crankshaft bolt but there are instructions on the site here that are very good.

If your belt breaks you are toastier than you are now. On the other hand.....

Is the noise synced to RPM? You may want to get an automotive stethescope and probe around before you dismantle the front end to look at the tensioner. About $10 at Autozone or similar place.

I have a rattle in mine but I think it is related to the flywheel or torque converter because I have been having transmission work done (and re-done) and it only occurs in D or R at idle.

The shop replaced my serpentine belt tensioner (easier) because they thought that was the cause. Obviously their experience led them that way from the sound. So yours may be the timing belt tensioner. Or something similar. But, you can eliminate and pinpoint items with the stethescope. I never had one in 45 years of looking at cars and bikes but can tell you that it is a GREAT tool to have.

 

That is a good idea. You would definitely hear where the sound is localized with a stethoscope.
As far as an intermittent sound - I recall when my timing belt tensioner gave out, i had an awful scary noise at idle, but when you rev up a little (over 1,500 RPM) the noise went away.

Doing a timing belt on a V engine is trickier than on a 4 banger. If you know what you are doing AND have another vehicle to use while working - it is a very rewarding job. If you have only one car and short on tools, it may be better to let someone else do it. Unfortunately the second option will cost you $$$.

 

That is pretty much dead on with the noise I am hearing. I've got it at the local shop today to take a look at it. I've looked at doing the timing belt before myself and it's just a little too in depth for me. I sourced a low mileage motor and priced an install...so if it ends up being the tensioner, I'd gladly pay to have the timing belt server from Mitsubishi rather than a motor swap.

 

I don't think you have to worry about getting a motor replaced. It sounds like you've caught the tensioner issue just in time and replacing a tensioner (along with timing belt) will make it all good and tight again. As far as not doing the job yourself - it is good to know where your limit of comfort is and not to get too deep into trouble by doing something you are not ready for yet.

 

Ended up being the tensioner. Nice and quiet now.