[JoshS98]

Second owner of this 325i, first owner babied the car and only drove 80k km in the 18 years he owned it.

I took it on its first “bigger” trip, 350km road trip, around 5-6 hours of driving. Random stops along the way at lakes and such.

About 4 hours into the drive there was a screeching noise kinda like someone was going “eeeeeeeee” the noise went faster if I accelerated and slowed down at lower rpm’s.

The noise lasted about 15 seconds and then faded away. Hasn’t come back since and haven’t heard it before.

I pulled over and checked everything, there was a strange burning smell from the driver side engine bay. Near the airbox and oil filter housing.

There was no smoke, and no visible leaks. Everything looked fine so we kept driving.

I first assumed it was my water pump as I’m pretty sure I still have the original but there was absolutely no warning lights about overheating on the rest of the 1.5 hour drive home.

Stopping at places on the way back, the smell was still present. Not as strong as it was initially but was still there.

Now we’re at the day after the road trip and the car still seems to smell from that area almost immediately after startup.

I’ve looked this up and seen the valve cover gasket mentioned. Previous owner had this replaced 2 years and around 10k km ago from what carfax seems to suggest.

Visually I can’t see any oil leaking from the valve cover gasket. The bottom side of the oil filter housing has a bit of oil sludge. Not necessarily wet to the touch but there is buildup. Besides that everything in the engine bay looks dry.

Below the car I do have some leaks coming from the oil pan gasket but I fail to see how this would cause a burning smell.

I thought it could have just been from driving the car hard. This is probably the first time it’s been driven more than an hour. Was more mountainey roads, lots of curves, inclines and declines but I was never pushing the car past how I would be driving with my grandma in the passenger seat. Wasn’t too hot out either, only around 16-19c

Went to pull codes from the car this morning (nothing besides a present AUC sensor code and a non present passenger occupancy code). After 6 or so minutes of sitting in the car reading those codes, I got out and could smell the exact same smell coming from the driver side engine bay.

I’ve so far ripped out my air intake, been looking all over and I can’t find the source of any leak or any wetness at all. The passenger side of the engine bay doesn’t smell weird at all. It’s definitely concentrated around the oil filter housing and air intake box.

I’ve smelled this smell before around cars, it doesn’t smell sweet. Not sure exactly what it is, My dad says it’s the smell or burning oil so I’ve been just going based off that.

[TriumphTim]

Hi, it is probably something related to the accessory belt on the front of the engine. A pulley or tensioner bearing is bad or going bad and the belt gets hot from friction causing the smell.

Your engine also has a electric water pump that is not related to the above belt. The pump is towards the bottom the engine, passenger side - not belt driven on the front like older designs.

The belt and tensioner service is pretty cheap and easy, I would look into it first before more complex jobs like valve or pan gaskets.

Good luck!

[JoshS98]

Originally Posted by TriumphTim

Hi, it is probably something related to the accessory belt on the front of the engine. A pulley or tensioner bearing is bad or going bad and the belt gets hot from friction causing the smell.

Your engine also has a electric water pump that is not related to the above belt. The pump is towards the bottom the engine, passenger side - not belt driven on the front like older designs.

The belt and tensioner service is pretty cheap and easy, I would look into it first before more complex jobs like valve or pan gaskets.

Good luck!

Hey, thanks for the advice.

Really think it has to be something with the belt you’re saying.

Got the engine cover off and the gaskets are spotless with no leaks. Spent a while going around multiple times, even took one of those blue shop towels and gently ran it over. Nothing was wet.

The smell seems centered around the oil filter housing. That gasket also seems to be perfectly fine, nothing is wet.

I did find my alternator seems to be absolutely caked with old oil presumably from a bad gasket at one point.

Can’t see where that could possibly be coming from with nothing being wet in the area.

I did take a video to see the belt and down into the engine. I’ll throw it on YouTube in case anyone has any ideas.

Thinking my alternator pulley could possibly be bad? The stench is coming from that area and it is covered in dried oil.

Any idea or easy guide on how to test and narrow this down?


video

[JoshS98]

Been digging into it more and the smell is 100% coming from around the deflection pulley attached to the alternator.

Smelling the alternator itself it doesn’t smell weird but if I get my nose close to that pulley it starts to smell burnt.

Closer to the tensioner and the front of the engine the smell dissipates. It’s definitely on the right side.

There’s no squeeling belt noise anymore but the smell is definitely still present.

Wondering if it’s worth it to just replace my deflection pulley. No idea if there’s a way to test if it’s bad.

I popped off the bolt cover and it seemed fine, there was a layer of oil on it but not much.

If I do go that route should I replace the belt and tensioner as well?

[TriumphTim]

Hi, great diagnosis work! Engine looks clean and no obvious issues.

If you release the tensioner you can slip off the belt, you can then test each pulley, you should feel or hear grinding or stiffness on the bad ones.

You need a bigger torx bit and breaker bar to move the spring on the tensioner, here is the kit and bits.

https://www.fcpeuro.com/products/bmw...t-kit-adk0022p

https://www.harborfreight.com/38-in-...ece-67886.html

[JoshS98]

Originally Posted by TriumphTim

Hi, great diagnosis work! Engine looks clean and no obvious issues.

If you release the tensioner you can slip off the belt, you can then test each pulley, you should feel or hear grinding or stiffness on the bad ones.

You need a bigger torx bit and breaker bar to move the spring on the tensioner, here is the kit and bits.

https://www.fcpeuro.com/products/bmw-accessory-drive-belt-kit-adk0022p

https://www.harborfreight.com/38-in-drive-star-bit-socket-set-6-piece-67886.html

Well shoot. Got the belt, tensioner and idle pulley replaced this afternoon and still smells absolutely terrible when running

Smelled my power steering fluid and doesn’t smell similar.

Smell is coming up from the alternator area. No smell anywhere else from the engine bay.

I’ve looked at absolutely everything for an oil leak. There isn’t one.

The CCv system has no oil leaks from the hoses into the foam on them.


The only oil leak is from the oil pan gasket. Doubt that could somehow make this burning smell.

My alternator wires are black instead of what seems to be the more common red.

Could my alternator just be absolutely filthy and dirty?

[JoshS98]

Can see how dirty the alternator is here, would’ve pulled it out already but don’t have new aluminum bolts to put it back in.

https://youtube.com/shorts/jfhoxb2j_...czZYLiKGkSK_cM