Allroad 2.5 tdi - squealing noise under heavy load

[craig_]

Hi, I've looked through all the threads but can't find anything specific on this. I have a 2002 Allroad 2.5tdi Tiptronic (only 78k miles total with new cambelt & water pump - but not idler wheels - at 63k) and it runs great except for when I'm towing my 1400kg caravan and putting it under load going up slight hills, usually in 4th. I get a squealing noise audible over the usual engine noise - not like a turbo whine more like the squeal of an alternator pulley on a lot of older cars when they first start up. It's impossible to tell where it's coming from as it's only audible in these specific circumstances. I have only just bought the caravan so have only just started hearing the noise - nothing wrong with the car at all unless towing. I'm just hoping it's not serious. Other posts have made we wonder about idler wheels - but is this likely and how serious is it?

[ceilidhalfie]

Sounds like noisy idler or tensioner. You could put lock carrier in service position, remove front covers and remove aux belt(s). Then rotate idlers, tensioners and pulleys to ensure all spin near enough noiselessly.
If all ok, suspect cam idler and or tensioner - this is more tricky as cambelts have to be removed - you will need to refer to the manual for correct procedure!
You are SURE cam idlers and tensioners were not replaced with the 63k cam belts change??
If you do end up removing cam belts, make sure you replace the tensioners and idlers - along with the thermostat.

[bagpipingandy]

Is it a harsh squeeling? maybe belts slipping?

I think the idler/roller noise would be there all the time, not just under heavy load,

regards

Andy

[Teflon]

Had something similar on my 2.5TDI but only when turning the engine off. It turned out to be the dual mass front pully - a dirty great big thing that cost a bomb to replace. I got all the belts done at the same time.

If you are having the front end and all the belts off be sure to give the pully a good coat of looking at to make sure it isn't the source of your squeal or a future problem.

[ametlib]

Would this noise possibly go away if you disconnected the electrical colling fan ?
Idler/ roller noise only under load is unlikely.

[craig_]

Thank you everyone for the suggestions. As there are a few different ideas here I think I will leave it for now and see what develops. Not always the best approach I know but with it only audible when towing and pulling uphill in high gear I'm not going to stress too much. Problem is a caravan holiday to Ireland is coming up. I'll just make sure I've got good car/caravan insurance cover. If it gets noticeably worse I will likely ask a local independent in Reading or Newbury to look at it as with no decent manual covering this model/engine I'm not sure how confident I'd be....... Also not too sure about disconnecting the cooling fan while towing a caravan - I guess a short distance couldn't hurt to see what happens. But why would this squeal only under load like this?

[ametlib]

My thought was that it may be loose. The only time the cooling fan will run in windpressure ( due to the speed of the car) is probably when this issue accurd.( Regarding my A6, the only time the cooling fan
runs at all, is when putting temp to "low" and start the AC, have to be very hot weather)
Could ofcourse be something else, but this is easy to check out.
I would also had taken a look under the upper cambelt cover ( cars left side) and checked if the injection pump belt run free. Use a torchlight and see that it is'nt laying against the wheel for the large cambelt.
Or maybe it's just your new waterpump that does'nt like the water to hot

[Peter D]

Small split in a boost pipe or even a hole in the intercooler. Whilst driving under this conidtion can you 'play' with the noise and does the pitch change. Regards Peter

[craig_]

Thanks again to everyone. I will have a look at the cambelt cover at the weekend. I should have mentioned the turbo was replaced fairly recently because one of the impeller blades got damaged and the pipes were checked over at the time. I would say the noise is definitely mechanical rather than a boost pipe leak - I've had that in a previous car and it wasn't this kind of " bearing squeal" which is the best description I have for this noise. I will check the intercooler too because another much earlier thread mentions that. I can't play with the noise particularly - not like the impeller whine I had with the old turbo. It is either there or goes pretty much immediately and completely when I lift off or when the 'box changes down (though this could be because I can't hear it over a higher revving engine). There is absolutely no sign of the noise under 'normal' driving no matter what I try. It only occurs with the extra load of towing. Very grateful for all the help so far. I only hope I can help someone else out in future.

[Peter D]

Are you sure the noise is not coming from the gear box not the engine. Regards Peter