BMW "burning rubber" odor/mystery

Factual Questions
1

Hi all,

Gatopescado’s thread inspired me to write my own. I am nowhere near as good a mechanic as he appears to be (and yes, I read about his oversight… That doesn’t mean he is a bad mechanic… He made a mistake, but he tracked it down and fixed it correctly… I think most of us who work on cars have made mistakes which we consider “dumb”, but when we solve it, that’s how we usually learn)

Anyhow, to the issue at hand…

Last week, my E46 had the low coolant light come on… No big deal, I thought… I would add when I got the chance. I noticed while driving about 6 miles into a 7 mile trip, a strange odor coming from either the engine or my vents… It smelled like burning rubber, at least that was what came to mind. When I got home, I put the car in park, put up the hood, and smelled all around the engine bay. Nothing. The smell was gone.

I figured I must have followed some guy who had put this smell in my nose, and I just associated it with my car. I put new coolant in, and the warning light went off. I ran the car in my driveway for over 30 minutes this weekend, just idling, and no smell. No leaks, either.

Today, I hit about the 5-6 mile mark, and the smell returned. Same thing… I stopped the car, left it running, and smelled around the engine. The smell was gone.

After sitting for a few hours, I drove the car home and the smell returned, and the check engine light came on. This was about a mile from home, so I drove home, parked the car and shut it off. I am positive the check engine light came on when it did, because after smelling the burning rubber odor again, I immediately checked for that warning light at each traffic light after smelling the odor. It came on between two traffic lights about 50 yards apart, maybe 1 to 1.5 miles from home. And of course, after getting in my driveway, before shutting down, I got out and tried to find the source of the odor. Nothing. It must be coming through my heat vents, but if it was coming from the engine, I would think the odor could be detected from outside if the car.

I thought it might be a failing belt. I thought perhaps the reason I am not smelling it as the car sits and idles is because whatever it is is not being used as it idles in the driveway… Something with the power steering, perhaps. But if that was the case, why the check engine light?

I checked the belts, and all look fine, at least from what I can tell. I haven’t torn anything down yet because I cannot afford to have the car sitting around for days. I will have to make a decision in the next day or so as to what my next step is. Try a fix myself, or take it to a shop. I don’t want to drive it again because I am getting the strong feeling that something is failing, and it is just a matter of time now, especially since the check engine light came on today. It isn’t worth the risk to drive it without having at least an idea of what is going on.

The car doesn’t knock or ping, and drives just fine. The heat is working perfectly. Steering is responsive, and I hear no noise at all when driving it… Just this mysterious “smell” and now the check engine light, of course.

One thing I just thought of… This summer, the A/C fan started blowing on and off intermittently. Turns out, my FSU/FSR (final stage unit/resistor) was bad and I replaced it. That repair went without any real issues, except that I couldn’t get one of the retaining screws back in place. The part is in securely, and this isn’t a problem. But could it have something to do with this repair? Could I be smelling something electrical, and that is why I can’t smell it from the engine bay?

Any thoughts appreciated.

2

Your next step should be to get the code read.

The burning rubber smell could be your catalytic converter overheating. That could be related to the check engine light being on either because the converter is bad or because there’s an engine management problem that is allowing unburnt fuel into the converter which will soon be bad if you don’t address it. I can’t imagine they’re cheap for this car, so I’d get on it!

3

+1 GreasyJacks suggestion, also look and see if antifreeze might be draining out of your a/c drain and dripping onto the exhaust. Usually it will drip on the floor but all cars are different. It kind of sounds like it might be a heater core issue.

4

Update,

Three different problems discovered with the car (what a shocker!)

Towed it into the dealership today, and the dreaded call came in.

  1. valve cover gasket leaking, which is what is causing the burning smell.
  2. thermostat isn’t opening completely, which is why the check engine light came on
  3. idler/pulley tensioner system was “squeeking” - it does… It just always stops squeeling after the car warms up. He claimed this one is potentially a show stopper, because if a bearing is bad and seizes up, it could explode, sending shrapnel everywhere.

I guess if ANYTHING in the engine failed and exploded, it would be bad. At the same time, the only reason I took it in was because of the smell combined with the “check engine light”, which turned out not to be related.

The price for each one of these repairs? Approx $500 each…

I don’t know. I don’t think I would know off the top of my head how to fix the idler/pulley system, so even if it doesn’t explode for 3 days or three years, if it is failing, it will probably fail sooner or later.

The other two problems are ones which I am not sure I want to do anything about until I get it home.

I can’t believe a new thermostat and a housing, with labor is a $500 job. Then again, I have never changed one on this car.

The valve cover gasket leak is something I could live with for a while until I can get it fixed myself… At least I know where the smell is coming from.
Any thoughts on the prices or on the ability for an average shade tree mechanic to do any of these jobs?

Thanks.

5

How handy are you? I’ve done the valve cover gasket on an M52 E36 and IIRC, they aren’t too different. Thermostat is pretty easy but you might have to pull the manifold so best to do it same time you do the gasket. Idler pulley isnt too hard, gotta pull the radiator so you’ll need to drain the system. Most of the difficulty is that its a tight squeeze in that engine bay.

Wish I could tell you what a mechanic would charge but I’ll warn you to only go to someone who works on Bimmers. They can be tricky for guys used to American or Japanese cars.

6

I’m not sure I understand why a blown valve cover gasket would cause a burning rubber smell. However a bad tensioner pulley would since it may allow the belt(s) to slip.

Having said that, and nothing, nothing at all about BMWs, I don’t know that a seized belt would cause everything to explode. In most cars it would cause your power steering, alternator and AC to stop working, but you’d likely still be able to get it home or to a shop with some careful driving.

Also, you could spray some belt dressing on the belt and see if that shuts it up. If it does, it may just be a bad belt and not a bad tensioner. Because, to me, that’s what it sounds like. Again, I could be wrong, but I don’t think a tensioner ‘warms up’, it’s either pushing hard enough or it’s not, it’s not that the spring pushes harder when it warms up and creates more tension. But that’s just a WAG (as is the rest of this post, FTW).

As for the valve cover gasket, you can replace them if you’re so inclined, but if you’re not, I’d stay away from a dealer and just have a mechanic do that. It’s probably a half hour to an hour job and, frankly, rather pay the neighborhood mechanic $75 rather then the dealer $150 to do it. It should be pretty stright forward. However, if you’re having a bunch of other stuff done at the dealer, might as well have that done to, assuming it’s actually leaking. If there aren’t a bunch of plastic fairings on top of the engine, it should be pretty easy to spot the leak.

7

These are all fairly routine items to replace so I don’t think a dealer is worth the $500/ea.

Valve cover gaskets leak as the engine heats up and once again as it cools down, that difference in expansion between the head and valve cover cause the oil to slowly ooze out. It’s not a critical repair really and it’s fairly straightforward to do.

Thermostat is another easy one, but, this needs to be done as this will prevent the engine from maintaining proper temp. A little messy as depending on where the valve is you might have to drain/refill the system.

Belt tensioner can be easy or hard depending on its location. And, he is right about it being a show stopper. If the pulley bearings are starting to fail and it seizes then the belt will at least slip if not bind and cause all kinds of ruckus. Looking quickly online it seems to be in a not-too bad spot, two bolts, and might as well put on a new belt. $35 on amazon and a new belt is probably about the same. Never worked on an e46, maybe two hours, anyone know?

8

Here is something to worry about.

I had burning rubber smell mystery on my BMW. No evidence of leaking oil or brake fluid that I could see. But the smell seemed to get worse, so I drove it the short distance to a garage. 100 yards before I got there, I ran over a small pot hole and…Bam, the car lurches to one side at the front, tyre blown. Luckily I was not going very fast and limped into the garage.

A shock absorber broke, it had obviously been scraping against the tyre causing the burning smell. Going over the pot hole made it puncture the tyre completely.

The garage did, of course, advise replacing all the springs at consider expense.

9

You are too kind! :blush: Truth is, I’m just a cheap-skate with lots of tools and time on my hands.

Wish I had something to add, but I got nothin’! All I can come up with is anytime I had strange odors in the car, it was a coolant leak somewhere. My 740 is renown for those. Water pump, radiator, heater valve…

I’ve done the water pump so often that the guy at NAPA knows my voice on the phone! Gotta love Lifetime Warranties!

I don’t know anything about the e46, but having worked on the e10, e30 and e38 I can tell ya the cooling systems aren’t too difficult to work on. The valve cover gasket should be pretty straight-forward without too much to tear apart. But like I say, I’ve got way too much time on my hands. The belt/tensioner stuff is real easy on the e30 and e38 actually. It looks scary as hell, but once you pull the hoses and radiator out, its all pretty much right there, and BMW really had some smarty pants designers and you are able to get to all the fasteners pretty well, in my experience.

This doesn’t really mean shit, but a friend out in Missouri has the same car as I do, and a shop charged him $700 to replace the radiator. I did the same job myself on my car for under $100. (I did spend two days on a 4-5 hour job however) But like I say, waaay too much time on my hands, major cheap-skate.

Good luck! Hey, what color is your car? :smiley: