Sorry to say...
Hi,
Ive had this exact same
problem.
The good news is that i can
help you diagnose the
problem, the bad news is that your going to need a new turbo.
I had this same whining noise (the one you describe as a police siren - im guessing it gets louder when you engage the power train right?)
At first i thought it was maybe a split pipe on the turbo intake. But soon discounted this as i was experiencing no power loss. (Turbos have to be a sealed unit and if there was a leak in one of the pipes you wouldnt be able to do more than about 20 mph)
After poking and prodding around with the
help of a very competant and very trustworth mechanic, we've been able to diagnose the
problem.
The bearings are worn on the impella unit inside the turbo. This is what is making the whining sound. It gets louder the faster you go as the turbo has to do more work and the impella spins quicker.
The good news is that currently this is not doing any damage to the car or the engine. However the bad news is it could end up being catastrophic.
Basically, with the bearings inside the turbo worn, the oil seal on the unit will begin to slip. Turbo units have no internal pressure to lubricate themselves and rely on engine pressure to draw oil over the bearings (ill tell you how youve damaged your bearings in just a moment). When the seal begins to slip, it will allow oil to be drawn up over the bearings and past the impella into the turbo unit itself.
When this happens you are in trouble. The turbo unit itself will start sucking in and burning oil along with fuel and air. When this happens you will jsee great big clouds of white smoke expelled from the exhaust. Thats not the bad part. The bad part is that when this happens the turbo will drain the oil sump very rapidly! If you see white smoke coming from your exhaust i would strongly advice driving it anywhere, unless its to get the turbo changed. Even then i would drive slowly to avoid engaging the turbo unit and make sure your topped up with oil. Even going so far as to ensure u have some with u and top up every few miles if needed! Im sure i dont need to tell you what will happen if you drive your car with no oil in the engine?!
I cant say how long it will take for this to happen, its like trying to estimate a change in the weather. If your looking at a rough price for replacement brand new from Seat they run about £1600 plus fitting for the BKD engine. (Thats a 2.0 TDI 140). However you can get a reconditioned unit with 24 months warranty for about £450. Obviously you have to have someone fit it, but its still the cheapest option. If you need a source for one id try Dave at Seremotors. You can find him on the forums. He's a really nice guy and helpful to boot.
As for why you might have damaged the turbo, some will just fail but others are done through turning the engine off too quickly. If you remember me saying the turbo has no internal pressure with which to use oil to lubricate the bearings, it relies on engine pressure. If you've been running the engine hard and using the turbo alot, then arrive at your destination - you need to leave engine idling for a minute or so. Turning the engine off too quickly cuts the supply of oil to the turbo whilst its is still winding down causing friction on the bearings which is whats causing the turbo to fail.
This was a common
problem with police cars a few years ago with their performance turbo engines. They'd run the balls off the turbo attempting to catch the crooks, then when they had to get out and chase the guys on foot, they'd pull up quickly, turn the engine off to take the keys with em and leg it after the "bad guys". The consequence of which, was the turbo still spinning with the engine off, and it caused a whole lot of cop cars to get sick!
Hope this helps you diagnose the
problem and offers you and everyone else some advice on this
problem. Dunno if alot of people have been having this
problem but its a pretty common
problem with turbo engines!
Let me know if you need any further
help or advice.
~Mike.