Engine noise - what's it likely to be?

matt_fsr

matt_fsr

matt_fsr

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Righto - I've got a noise coming from my engine, but I'm not good enough to figure out quite what it is. I doubt it'd record well, but its a kind of whistling sound, very much like either a belt that's slipping slightly or some bearings that are running without grease.

It seems to only happen at idle, or when the engine is under no load.

Thoughts on what its' most likely to be?

Depending on the cost of repairing it will depend on how likely I am to fix it, as it's only an annoyance at present :p

Cheers
 
What's the car? A belt sounds like the best place to start but it's impossible to say without more detail on the car and where the noise is coming from.
 
rodenal said:
What's the car? A belt sounds like the best place to start but it's impossible to say without more detail on the car and where the noise is coming from.
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Fully understand.

Car is a Mercedes C180, the noise is coming from the engine bay but I can't pin down exactly where, my hearing isn't great for directional things like that. :(
 
Can you put it to a general direction i.e is it the belts side / end of the engine?

If so start by checking the condition of the drive belt(s), if they look fine (can still see the writing on the smooth side, no cracks or fraying on the ribbed side) then take the aux belt off and run the car for a minute. If the noise goes either your belt or one of your tensioners / pullies (including the alternator) are the cause. Start by putting the old belt back on and spraying some wd40 into the pullies you can see, one at a time to see if the noise stops - noting which one gives the issue. I would buy a belt before doing this, you'll be putting a new one on when you're done regardless of the cause. If you can't identify the culprit from this and the new belt makes no difference then we need to consider other possibilities.

If the noise is not coming from the belt area, take as long a screwdriver as you can and start sticking it against bits of metal with your ear to the other side, you'll soon pinpoint where it's coming from. I should say it's fairly unlikely the noise will be from anywhere other than the belts.
 
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rodenal said:
spraying some wd40 into the pullies you can see.
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There are very very mixed opinions on spraying WD40 on belts in the engine bay ranging from, don't do it to only on old cracked belts. Hairspray is an alternative but would just be a short term fix. There 3 basic rules with noise from belts;
1. Worn out belt = replace it.
2. New belt = needs tension adjusting.
3. New belt correctly tensioned = whatever its turning is faulty/wearing out and becomming difficult to turn/other annomaly.

However, the OP said
matt_fsr said:
...its a kind of whistling sound, very much like either a belt that's slipping slightly or some bearings that are running without grease...It seems to only happen at idle, or when the engine is under no load.
Click to expand...
a belt squeals not whistles and it won't just make the noise at idle - but will vary and fade with revs or squeal across the rev range.

A 'whistling noise' is more likely some sort of vacuum leak on the intake side such as a hole in an air tube or a loose/failing connection somewhere on an air/vacuum hose. When the engine is idling the airflow is at the right velocity to produce the 'noise' as it flows across the hole/gap/split - when you put the engine under some load the airflow increases sufficiently to stop the noise.

With engine off do a visual check, follow your hoses from the air filter to the carb/throttle body then to the intake manifold - looks for splits or holes or perished rubber. If nothing, turn the engine on and when it starts making the noise, do the same, follow the hoses and you can even gently squeeze them, move them and if the noise changes or dissappears then suspect the hose you've just squeezed/moved. Worse case scenario - perhaps your inlest manifold gasket has developed a leak :(
 
xMarkie said:
a belt squeals not whistles and it won't just make the noise at idle - but will vary and fade with revs or squeal across the rev range.
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Very good point - I'll give it a run through some other rev ranges on the way home tonight, but I'm almost certain it is only happening at idle.

Wouldn't surprise me if it is a hose issue somewhere, the car is 14 year old and I have no service history for it. When I got it, it would drop revs when the clutch was dropped down to about 500RPM, and be in danger of stalling - until I changed the rather manky air filter, and all way well again!
 
To try and isolate where the noise is coming from, get the cardboard centre of kitchen tissue and point it at various components until you isolate where the noise is coming from..
 
xMarkie said:
There are very very mixed opinions on spraying WD40 on belts in the engine bay ranging from, don't do it to only on old cracked belts. Hairspray is an alternative but would just be a short term fix. There 3 basic rules with noise from belts;
1. Worn out belt = replace it.
2. New belt = needs tension adjusting.
3. New belt correctly tensioned
Click to expand...


Would only be using g the wd40 to identify bad pulley not to fix it, you're right though I've jumped the gun and not thought about the difference between a whistle and whine
 
Having a listen to it on the way home, it's definately metallic not an air-whistle - and also seems to be more pronounced when the engine is cold.

By the time I got home, the engine was hot and the noise had gone - but it doesnt always go.

I'll try and ID where in the engine its coming from tonight - cheers for the advice so far.
 
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