We are a Diesel Turbo Specialist workshop in South Africa.
The Citroen C4 1.6 HDi turbo has been replaced last year November because of the Turbo Wailing like a police siren.
The car came back last week with the same noise to the turbo, so I took the turbo off to inspect to find
that the Turbine blades ( hot side ) have been damaged from foreign object from the engine. The foreign object
hit it out of balance so that's why it sounds like a police siren. A Citroen specialist says it can be carbon build up in the engine that can cause this? The engine still runs smooth with no problems.
I will insert some pics to show this.
We have fitted a new turbo and the car seems to be fine, no probs.
There are big problems with poor oil change routines on 1.6HDi's causing oil clogging in cylinder head galleries, turbo supply lubrication pipes etc which is the cause for repeated turbo failure.
When replacing a failed turbo it is imperitive to replace the oil supply/return pipes. You also need to remove the sump and check the gauze on on the pump for any blockages.
Finally a good check so see if there is serious internal blockages, remove the brake vacuum pump - there's a little gauze inside that. If that has signs of blockage then you've got some serious internal clogging going on.
We've had a brand new turbo literally fail within 100 mile from the impellor seizing up and the nut which secures it on the shaft coming undone and wedging in the fan blades. This particular one was an extreme case and ended up having a new engine!
C6 Dave wrote
It's possible that all the carbon build up is due to poor oil quality.
The HDi's require a 'Low Saps' oil
There is an ongoing thread here on oil: - Click Here -
The thing to realise if using a forum such as this for information, is that just like Wikipedia, because it's posted does not necessarily make it true. For example, buying an oil just on SAE viscosity rating is a recipe for problems: the industry in Europe (ie ACEA) stopped using this other than as a marketing label years ago.
The nasty end of the lubricant blenders/marketers can use some pretty cheap base stocks, throw in some polymers and the viscosity ranges (SAE variety) will look fine on the can. Might not last very long in the engine though.
There is a good presentation on Southern Lubricants website by Total explaining the thinking behind ACEA service fill specifications for PSA FAP equipped diesels like our 2.7HDis - Click Here -
In the Lube Library under Total open the presentation named Low Saps details
Look at the photo of the fouled EGR valve when using a normal non "low SAPS" oil.