Strange noise!

[steve811]

Perhaps someone can help with this! On my CDTI sometimes when the car is running I get a strange noise from somewhere in the engine/heater area. The best way of describing this is like an air raid siren starting up! It only lasts for a second and does not seem to indicate any real problems. Am I right in thinking it is a the ATC closing vents or something? Or is it something more sinister?:confused:

[Parker]

could it be more of a whooping or whale sound? If so nothing to worry about a common fault to do with aircon. A re-gas stopped mine when done last summer.

[steve811]

could it be more of a whooping or whale sound? If so nothing to worry about a common fault to do with aircon. A re-gas stopped mine when done last summer.

Air con in Feb?

[Mike Noc]

Perhaps someone can help with this! On my CDTI sometimes when the car is running I get a strange noise from somewhere in the engine/heater area. The best way of describing this is like an air raid siren starting up! It only lasts for a second and does not seem to indicate any real problems. Am I right in thinking it is a the ATC closing vents or something? Or is it something more sinister?:confused:

Sounds a bit more sinister - check your cooling fan is working. Air con is going over pressure due to lack of cooling - does it happen when you are stopped or in slow traffic?

These diesel engines very rarely need the cooling fans here in the UK but the air con does.

Mike

[steve811]

Sounds a bit more sinister - check your cooling fan is working. Air con is going over pressure due to lack of cooling - does it happen when you are stopped or in slow traffic?

These diesel engines very rarely need the cooling fans here in the UK but the air con does.

Mike
I can't see that, as it sometimes happens when the engine is very cold, but not when the engine is hot on a long run. Will check out the fans though.

[Jules]

Perhaps someone can help with this! On my CDTI sometimes when the car is running I get a strange noise from somewhere in the engine/heater area. The best way of describing this is like an air raid siren starting up! It only lasts for a second and does not seem to indicate any real problems. Am I right in thinking it is a the ATC closing vents or something? Or is it something more sinister?:confused:

Is it on the overrun or light throttle settings per chance?

[Mike Noc]

I can't see that, as it sometimes happens when the engine is very cold, but not when the engine is hot on a long run. Will check out the fans though.

Steve nothing to do with the engine - the same cooling fan is also used for the air con. Thing is if it happens with a cold engine then the air con probably hasn't had a chance to go over pressure so not what I thought it was.

Does it happen with the econ button activated?

Quick way to check the fan: start the car and put air con to its lowest setting - the fan should be running even with a cold engine.

Best way I could describe the noise I heard when mine went was like an elephant trumpeting rising in tone slightly at the end!

Mike

[steve811]

Is it on the overrun or light throttle settings per chance?

No, very often when the engine is at idle

[steve811]

could it be more of a whooping or whale sound? If so nothing to worry about a common fault to do with aircon. A re-gas stopped mine when done last summer.

I think your right, it is very much like a "whale song"! The car is due an MOT soon so I will get the aircon checked at the same time before the summer.

[Jules]

No, very often when the engine is at idle

Then it's probably your Cooling/AC fan which is rarely used for engine cooling on diesels. Mainly used to cool the Condenser which in turn protects the compressor.

A simple DIY fan test is to set heater ATC to DEMIST mode.
Radiator fan as viewed through front grill should operate simultaneously with the compressor.

Whooping is caused by overpressure of the AC gas, due to lack of cooling.
(not an ideal situation!)
Plenty written on the subject