Disco 300TDi - turbo destroyed

[mahon257]

Whilst setting off back from NW Scotland to Norfolk last week in my 1996 Disco 300TDi, driving throught the highlands, I noticed my Turbo pressure "peak" had dropped from a previous high of 20psi to 10psi.

The pressure drop was, accompanied by, well, what sounded like a bag of loose change rolling around in the engine, between 1,000rpm to 2,000 rpm - with revs higher than 2,000 the noise went away.

So, somewhat optimisically, 600 miles from home, I decided to carry on (stupid, I know). I managed to do another 500 miles of the 600 mile journey - before, a sudden burst of white smoke, followed by a total loss of engine power, where upon I ground to a halt by the side of the A1.... The AA man turned out to be a 200tdi owner (good bloke too), when I explained that the engine would tick over, but wouldn't run - and I told him the turbo pressure story. He pulled off the airhose, from the air box - to the turbo, and stuck his finger in the back of the turbo. "that's the problem" he said! The turbo shaft is now loose - and you can move it about 1cm in all directions (in other words, it's completely "shafted").

I have a second hand turbo on order from eBay....

My question is this... If I remove the turbo and find "bits" missing, i.e. fins, bearings etc, where could the bits have gone? Stuck in the CAT in the exhaust? or intercooler? or worse? What would the logical sequence be for turbo bits if they separated from the turbo? (I don't fully understand the airflow path after the turbo).

In other words, how much of the engine do I have to dismantle? could I get away with just bolting the replacement turbo on?

As you can tell, I am a complete amateur at this sort of thing! But would like to give it a go - if only for the sake of learning more about the engine..

Any help, as always, greatly appreciated.

[Aragorn]

There are two wheels, one on the inlet side and one on the exhaust. Clearly anything thats disintegrated in the exhasut side will have just been fired down the downpipe, and if the catst still fitted will be stuck in there as you suggest (perfect time for a decat pipe!)

The other wheel is on the inlet side, and blows air thru the intercooler then into the inlet manifold into the engine.

I would start byremoving the intercooler and giving it a very good clean out to try and remove any bits of turbo that may have found their way in there, then remove the pipework to the inlet and have a look inside to see if there are any obvious bits in there. You could remove the inlet manifold and clean it out as a precautionary measure, as if your replacing the turbo you'll need a new gasket anyway.

Other than that its a case of fit the new turbo and prey nothings ended up in the cylinders.

[BogMonster]

Yep I would go with the above ^^^ the intercooler will filter out all the big lumps on the inlet side, but flush it through and give it a good bang out and some compressed air through it the wrong way to dislodge anything jammed in there. You'll soon know if there is a problem - bits of metal in the cylinder tend to produce all sorts of nasty noises when the engine is running. If it sounded ok at tickover when you stopped it then you have probably got away with it.

A tip to clear out the intake system after you have flushed it with degreaser is to forget using a compressor (not enough airflow) and connect it up to the turbo but leave the final rubber intake hose (intercooler to inlet manifold) off at the manifold end - start it up and let it idle for a bit, and then give it some sh** on the throttle to 3000rpm+ - point the loose end of the rubber hose away from anything absorbent that you wanted to keep and definitely don't look down the end of it as a fairly significant amount of oily carp will come out at very high speed! Obviously you need to make sure nothing can be sucked into the inlet manifold while doing this.

[Aragorn]

Erm, i wouldnt do that ^

The turbo governs its speed using an actuator that responds to pressure in the inlet. With the pipes disconnected there is no way for pressure to build up and the wastegate stays shut, this means that the turbo WILL overspeed if you gun the engine, and can kill itself doing so.

seen as its only the intercooler and two rubber hoses, i'd just stick with giving them a good flush with some degreaser/petrol/thinners and let it all dry off properly before refitting.

[Les Henson]

If you rev a stationary turbo engine, then the wastegate actuator won't work - no load on the engine ??

This is why boost pressure can't be checked/monitored without actually driving it.

Or am I missing something?

Les.

[Timmy511]

Erm, i wouldnt do that ^

The turbo governs its speed using an actuator that responds to pressure in the inlet. With the pipes disconnected there is no way for pressure to build up and the wastegate stays shut, this means that the turbo WILL overspeed if you gun the engine, and can kill itself doing so.

seen as its only the intercooler and two rubber hoses, i'd just stick with giving them a good flush with some degreaser/petrol/thinners and let it all dry off properly before refitting.

so long as there is oil pressure and the turbo its self is in good fettle i cant see there being a problem.

When doing a burst test with a big hole drilled in the turbine wheel or comp wheel the turbo will run for quite sometime befor it lets go, and thats running at stupidly high rpm and with the manifolds glowing red.

id much sooner not worry about you exhaust, id be more worried about oil contamination and your intercooler.

to be 100% safe, change you oil and filter, runing it for a short while (couple of days of low milage) and change it all again. then just swap the intercooler for a cheap second hand one off a breaker, youll get one for a tenner and have more piece of mind!

when you fit the turbo, prime it with some clean engine oil just to ensure its got some clean lubrication on first start up.

Tim (ex Holset/Cummins Turbo Technologies employee).

[BogMonster]

Erm, i wouldnt do that ^

The turbo governs its speed using an actuator that responds to pressure in the inlet. With the pipes disconnected there is no way for pressure to build up and the wastegate stays shut, this means that the turbo WILL overspeed if you gun the engine, and can kill itself doing so.

seen as its only the intercooler and two rubber hoses, i'd just stick with giving them a good flush with some degreaser/petrol/thinners and let it all dry off properly before refitting.

Not unless you are doing it with the engine on load - producing boost and thus lots more exhaust gases. In any case it doesn't take more than a few seconds to redecorate the bonnet padding with the contents of the intercooler

[cipx2]

The highest turbo pressure I can get from my stationary 300 Tdi by flooring the pedal from idle (thus using only the engine internals' inertia as a load) is about 0.55 bar for a fraction of a second. At high constant revs (3500?) and no load the pressure is almost zero (0.1 or something).

There's absolutely no way you can over rev the turbo when the engine is not loaded (or under a low load).

[Aragorn]

I guess i wasnt considering that the engine wasnt being boosted and therefore the usual rapid increase in exhaust gas flow that results when it comes on boost doesnt happen.

My other car is an Audi A4, and from using the forums over there the S4 model is very prone to boost leaks from the rather crazy pipework. The usual result though is the boost leaks without the driver being aware, so the turbo is constantly working harder to make up the difference, (IE the managements asking for 8psi, and the turbo is delivering it, but due to the leak its running way way faster than the usual RPM required to make 8psi), and the first the driver knows about it is the turbo letting go.

As you can imagine therefore the first thaught of the turbo running unrestricted is "aargghh its going to die..." but without the boosted airflow i can see how the engine cant actually get the turbo up to dangerous speeds!