My 2003 MCS with 155,000 miles recently started rattling from the passenger side of the engine compartment. The car has a 15% supercharger pulley, a widened airbox, and has had one of the baffles removed form the exhaust. It's had no other modifications and has run well for a while. A week ago I noticed it rattling on cold start, and the sound has gradually become more frequent and pronounced.

Having read about the various causes of rattles in R53s, I haven't been driving the car much. I'd like to fix the problem myself, but I'm having a difficult time figuring out the source of the rattle.

Some other potentially relevant information:

Two weeks earlier I noticed that the radiator fan was "running on" for some minutes after I turned the car off. This had never happened before, and was now occurring one out of three times I drove the car - no matter whether the drive had been long or hot. So I started to think I might have a temperature control problem of some sort. But the problem seemed to go away, and I never figured out the cause.

And this week the car threw the P0136 code for an O2 sensor issue. I reset the code, just to see if it was a fluke - and it has not returned. But as I said earlier, I haven't been driving it much, so it may very well come back.

So my questions for the many Mini scholars on NAM are:

What is the source of my rattle? The supercharger? Chain tensioner? How do I find out?

And do you think these symptoms are connected?

 

First step...
Top off you coolant tank....common cause of a run on fan is low coolant...
Next, with the car running...
Push your clutch is...and see if the rattles goes away...if it does, throwout bearing on the cluch is failing...mine rattled for about 60,000 miles...

 

Some good suggestions above. If the P0136 code does come back, try some of the possible solutions here. Does the rattle go away once the car comes up to operating temps? Can you pin point approximately where it may be coming from? i.e. under the bonnet on the drivers or passenger side? This guy here had a similar issue and it ended up being the timing chain tensioner. Maybe some of the information in that thread may be helpful to your diagnosis.

 

Thanks for the replies. Good initial thoughts.

When the fan first ran on, I checked the coolant tank and the fluid level was at the "max" indicator. I just checked again, and the fluid level is the same. So I don't think low fluid is involved there.

The rattle is persistent whether I push in the clutch or not, so I don't think it's clutch related.

The rattle is coming from the passenger side, but I can't really tell where it's coming from exactly.

The rattle seems to occur most noticeably at low rpms, just above idle - between 1,100 and 1,300. When I first noticed it, I only heard it at start up. Now I hear it at low rpms all the time, and sometimes even at higher speeds. This makes me think the chain tensioner might be the culprit.

Also, if the noise were coming from the supercharger, and the PTO gears were wearing out, wouldn't the noise be coming from the driver's side?

 

So a bit of an update and some followup questions:

The rattling is much diminished, the PO136 code has not returned, and the fan doesn't seem to run on often. As much as the car seems to drive normally, I am not stupid enough to think the problem has gone away. Rather, I am scared that whatever was rattling has broken in some way such that it no longer rattles.

Also, I think the car may be running too hot. It hasn't overheated; and I don't have a scangauge type device, so I have no way of knowing the actual running temperature. But it feels much hotter than before when I open the hood after driving it, and sometimes I get a faint whiff of something burning.

At this point I'm guessing that maybe the supercharger pto gears wore out (causing the now-gone rattling) and are no longer driving the water pump. Before I tear everything apart to investigate, I'd like to know if I'm barking up the right tree.

What do you guys think? Sound like a supercharger/water pump issue?

 

If you can still drive it, it's definitively not the PTO—engine lifespan with no water pump is measured in minutes. When it goes, You'll Know™.

I have a rattling from the passenger side, too, but it only occurs under load at about 2000-3000+ rpm. It's either the alternator bearing or the crank pulley, as far as I've been able to diagnose.

I would look at the chain tensioner first, if I were you.

 

Update: The source of the rattle has been found and fixed. It turned out to be the heat shield scraping against the exhaust manifold.

One of the bolts retaining the heat shield had come loose and fallen out, but I couldn't tell because the sheild didn't move or vibrate unless the car was moving. Eventually the heat shield vibrated enough that the metal tore away around the remaining bolt, leaving the shield sitting loosely on the exhaust manifold.

I had been scratching my head trying to track down this rattling, looking for loose parts under the car and listening to various running parts with a metal probe, with no luck. Finally a friend from NAM noticed the obviously out of place heat shield yesterday. Sometimes it's good just to have a second set of eyes on the problem. (And, in fairness to myself, the heat shield hadn't yet torn off when I looked last week.)

Anyhow, the rattle is now gone!