I have an 05 stock MCS that has developed a strange engine noise. It's quite loud and sounds sort of like a bad bearing type noise from the passenger side of the engine. (At times, it sounds like a transmission from outer space.) I have replaced the belt and the belt tensioner but it did not fix it. It will happen randomly but usually when the AC is turned on. The AC still blows nice cold air though. What is strange is that it doesn't seem to change pitch or tone when the engine is revved. So, it doesn't appear to be directly connected to engine RPMs. ??? This is quite puzzling. ??? Does anyone have any ideas? Thanks.

 

Did you feel the idler pulley? Mine had a bad bearing once.

 

is it a knock or tap ? is it in time with rpms?

 

how many miles and what tranny do you have?

 

When I replaced the belt and tensioner, I only briefly checked the other pulleys. They did not seem obviously bad, but I did not check them extensively.

The sound is not a knock or tap. It's difficult to describe but I'll try. It sounds like something scraping sort of like metal on a brake rotor, but at at decent rpm but not ultra ultra fast. (it's not the brake rotors because it happens when the car is still.) The sound was intermittent, randomly off and on for a few seconds. It is NOT in time with the rpms of the engine or the speed of the car.

It has about 60k miles and the manual 6 speed.

 

The sound has now evolved into a constant whine type sound. It starts only after I press the A/C button. It does not change pitch with the engine rpms. It also does not change pitch if I change the fan speed. It will continue even after I turn the A/C button off but sometimes it will eventually stop after that. I have the stock A/C and not the one with the advanced controls. It looks like it will have to go to the shop. If anyone has any ideas on what this could be, it would be helpful even if I cant fix it myself. I dont want to needlessly have to buy a new A/C compressor. Thanks.

 

maybe clutch on a/c sticking? causing belt to have to slip over a/c pulley

 

You would think that it might be the A/C clutch but the sound doesn't change pitch with the engine rpms. If I rev the motor it still sounds the same. If the pulley was sticking, it would smoke the belt. Could there be anything within the A/C system that moves but independent of the engine rpms? maybe something plugged up inside or maybe contaminated refrigerant?
It not starts to make the noise about a minute after pressing the A/C button and it continues about 2 to five minutes after I turn it off. The A/C is cold, so it seems like it's working but it just sounds awful.

But if it is the A/C clutch, can that part be replaced without a whole new A/C compre$$or?

 

pull the belt and check all the pulleys by hand . listen for noises . then with engine cool, start it up with belt off and listen. you got a little time till it overheats so dont panick ,but make it quick .

 

No. The clutch is not available separately. I had a compressor clutch fail two weeks ago and the bill was $1450. Not fun. But it didn't make any noise first. Just stopped working.

Hopefully this is not the last throws of your supercharger.

///Rich

 

I'm not convinced that it's the A/C clutch. It's directly linked to the belt and therefore connected to the engine rpms. The noise doesn't change with a change in rpms. That would also hold true with the supercharger. What would rule out the supercharger too is that only happens when the A/C button is on and lit.

I could just buy a louder stereo to mask the noise, but I would probably have to spend a few hundred bucks on some stupid special BMW tool to get the old one out.

 

pull the belt and check all the pulleys by hand . listen for noises . then with engine cool, start it up with belt off and listen. you got a little time till it overheats so dont panick ,but make it quick . ____


you gotta start eliminating things pulling the belt will eliminate all pulleys other than crank. then you can check other pulleys with hands and ears one at a time ______________

 

Since the belt is directly connected with the engine RPMs, then it would be a logical assumption that the belt and any pulleys are probably not the cause.
Also, running the engine without the S-belt is a recipe for disaster and could potentially totally destroy the engine. However, I did remove the belt and checked the pulleys (without the engine running!) and none of them appeared bad.

I am wondering if there are any small electric motors, within the engine compartment that may connected to the A/C somehow. The noise sort of sounds like one of those going bad. The sound now sometimes will happen when the engine is off but the ignition key is on.

 

so you're saying you dont trust yourself to start the cold engine and run it for 30 seconds without the water pump? ever been drag racing? the cars not gonna overheat in 30 secs which is plenty of time to determine if it's a pulley issue or deeper . not sayin drive it around the block .
p.s. the timing is behind the timing cover so you wont destroy much of anything; it has it's own chain to the cam ; but you go ahead you seem to have it all under control .

 

 

Even with the belt on, the engine would need to idle 5-10 mins before the thermostat opens up to let coolant circulate. Before that, the coolant is actually standing still.

 

Besides the risk of an overheated engine, there is a risk of a dead battery and damaged alternator. Since this is a supercharged engine, the lack of a spinning supercharger could potentially have seriously ill effects on the engine too. Running the car without the s-belt will most likely trigger a lot of codes and errors within the computer that I don't want to waste my time clearing.

However, since the noise does not appear to be related to the engine RPMs, running the car without an s-belt won't help in diagnosis. Therefore, arguing about whether running a car with or without it is pointless, no matter who is right or not. So let's move on....

I am now suspecting that it could be the power steering fan. So, the question now is, when is this thing programmed to kick in? Is it wired somehow to the A/C, which would explain why it happens shortly after the A/C is switched on, and why it happens randomly at other times, perhaps when it heats up? I haven't had a chance yet to check it in more detail but after closer inspection, it sounds like it is coming from the rear of the engine in the middle of the car.

 

while idling you are at high vacuum / no super charger in the equation due to bypass valve . battery will not die in short period like this, you could run it for a very long time before battery death . and a crank bearing sometimes doesnt change noticeably with rpms just groans along nicely . check the pcv valve pipe(elbow) to see that it's not collapsing. makes a very load groan .

 

I'm just saying that from my experience the risks you mentioned (overheating, dead battery, damaged alternator) don't exist by running the engine w/o the belt for a couple of minutes. If that was true, a high percentage of batteries & alternatorswould go kaputt when belt snaps while people are on the freeway. If the supercharger stop spinning, the combustion chambers receives less air pressure. That's it... nothing will happen to the long block.

It will definitely trigger error codes which may cause inconvenience. I keep a cheap $30 OBDII scanner in the car for those instances. You can clear all hard codes with 3 clicks of a button.

I've drained the cooling systems in my Porsche 944S, Audi 4000, VW New Beetle (turbocharged) by running the engine (from cold) with the radiator drain valve open till all the coolant is out... which is a few minutes. The oil pan was barely warm to the touch.

For the engine to begin to overheat, the oil temperature must be over 300*F. At idle, that would take at least 15-20 minutes with no coolant in the engine.

Anyhow... good luck with your diagnosis.

 

so no catastrofic damage to the porche? unpossible!!!!!!!

 

That's right. It's beyond impossible... it's UNpossible.

Kidding aside, the cooling system in my 22 yr-old 944S (4-cyl, 2.5L) is the most robust of my cars. The highest temp I've seen it is about 195-200*F. It has a huge radiator with enough capacity to cool a V6, and 2 fans which are usually never on during freeway speed. When I used to live closer to the beach with light traffic and Hwy speed of 35-50 MPH, the fans kicked in maybe 10-15% of the time. Ambient air has to be 85-90*F for them to wake up.

Ranking by design and reliability...

1. '87 Porsche 944S (2 fans, biggest radiator)
2. '01 VW New Beetle 1.8T (2 fans, reserve level sensor, coolant also cools turbocharger bearing jacket)
3. '06 MCSc (1 fan, lousy resistor, no level sensor, pump is spun by SC shaft)
4. '81 Audi 4000 (1 fan, smallest radiator... removed the thermostat and it's cool as a cucumber, except for 1 time I drove to Phoenix in 120*F heat... my eyes were glued to the temp needle

What's disappointing is my older VW New Beetle has a much better design than the newer and $10k more expensive Mini.

Now onto the regular program...

 

now this is gonna start some stuff here but i was taught that the thermostat also helps keep a n engine cool by holding the coolant in radiator till it opens ; then as temps come down it closes ,holding coolant in radiator cooling it and on and on . so if it's opening and not closing again doesnt that indicate a radiator that's too small ? or does it flat just stay open in summer? like the coolant entering block should be cool enough to cause therm to close no? or it just stays open in summer and only cycles in winter ?

 

If a cooling system functions correctly, coolant leaving the radiator going to the block is always lower in temperature.

A thermostat's aperature is determined by the coolant temp at the block. Most thermostats begins to open at around 180-185*F (85*C), or roughly 30*F below the boiling point of water. In SoCal (even in winter), only 10-15 minutes of driving will crack open the thermostat. Once opened, it remains open because the oil temp is high enough to keep the coolant temp hovering around 190-200*F. Once removed, both my Audi 4000 and a friend's AMC Gremlin had slightly lower temp reading (during normal operation) and much lower reading when ambient temp is 90*F and above. Of course, both cars took longer to warm up during the morning because there's nothing there to block the coolant from circulating.

However, if you're in colder climes, the thermostat might close slightly or decrease its aperature to slow down the coolant circulation to keep the engine from cooling down below the normal operating temperature. Fuel Injection programming relies heavily on correct coolant temp reading. That's why faulty coolant temp sensors will cause the ECM to go into limp mode and run rich and kill gas mileage.

Removing the thermostat is an old trick that should only be done for older cars in hot climate. I wouldn't do it for cars in colder climate as it would take 30 minutes before the heater begins blowing warm air. If you have an aircooled VW or Porsche, you know how that feels!!!

 

I had the same exact problem with my 05 MCS. It turned out to be the power steering fan going bad. It turns on with the A/C and will run for a while after the A/C is turned off. It is very easy to replace. Just two bolts and one wire connection. The fan was the first part I replaced on my car.

 

Yes this sounds exactly what is happening. Since it's not connected to the serpentine belt, it doesn't change with engine rpms. It starts making the noise at the same times you describe and is sounding like it comes from that general area. I wont have a chance to look at it in more detail until the weekend though.

Thanks.