Dead Turbo - 1.9 Tdi

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Originally Posted by cogdoc

Doesn't help a lot of 103's will probably be driven by people ignorant of off boost turbo surge, basically putting the turbo at risk.

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Originally Posted by peter

How can its occurrence or effects be reduced?

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By not using large amounts of accelerator pedal at low revs. Or to put it in another way, keep the engine above 2,000rpm anytime you want it to do a decent amount of work (ie anything more than gentle acceleration or climbing a distinct rise). This will also help prevent the variable vanes in the turbo from sticking and causing an "over-boost" condition.

Just because a TDI engine will pull hard at low revs doesn't mean it is good for it.

I'm in the market for a MKV. I have to admit it's pretty scary to read all this negative feedback (but I really appreciate that it's here).

Turbo surge is basically what Greggo said, where you place a high demand on the turbo at low revs with high load, like driving along in 5th or 6th at 60-80kph and putting your foot down. The engine isn't flowing much air, the turbo tries to boost, and it's basically overboosting against an engine that won't flow the air. At higher rev's / lower load, the turbo can flow against less restriction ( the valves are open more basically ) and it's far less likely to overboost. The turbo impeller starts to try and push against the pressure it has developed which isn't going anywhere, and it basically cavitates against reverse pressure waves putting TREMENDOUS load on the shaft. Generally it shears the impeller off on the cool side.

All you can do is change down gears ahead of asking the turbo to work, go easy on the throttle in such situations, or just be aware that below the "boost" range, which is about 1700rpm, your chance of surge is far more likely.

In my mind DSG cars wouldn't suffer this problem anywhere near as much, as the box would change down automatically.

Engineers walk the tightrope of having a turbo that will give the desired top end power output, be responsive, boost own low and remain out of the dangerous surge area as much as possible. That said, in the wrong operating parameters virtually all turbo's experience some surge.

Sounds like the turbo is being asked to do too much work in this design.

Am I correct in assuming this issue is more likely to effect a diesel engine as the rev range is different to petrol? As stated, any turbo could be put under this load, sounds like the ECU is too demanding or the turbo is just not strong enough...

It seems to have been a particular problem with the earlier 1.9 Tdi, rare on the 2.0L and I haven't heard of a problem on the petrol burners.

Hopefully the newer turbos are a little more robust.
Might pay for me to get my wife to read the driving tips r.e. turbo surge (she sure doesn't like driving critique from me!).

Hoping to pick it up this arvo.

Affects ANY turbo but diesel demands on a turbo are typically higher, given higher boost pressures.

Here's a great link and study of surge on the VNT15 in the 1.8 T Audi A4 for those of you who want to get right into it.

http://forums.tdiclub.com/showthread.php?p=417918

my theory is basically that the VNT is so effective at low flow spooling that it is cabable of far worse surge than older conventional turbo's.

VNT turbochargers are capable of producing way more boost at low rpm than normal internal combustion engines are able to use, so really it comes down to control - VNT's are still pretty new and manufacturers are still really learning how to control them for longevity. They are trying to balance cycle life, performance and emissions... bound to fall over sometimes :-)

Hmmm, good point mate, one of the things VW goes on about with the 125kw is the far more accurate control the VNT mechanism has over the prior 103. I never really thought it was a big deal, but it would now seem it is!

i'm waiting for my Caddy to go pop

Nearly three weeks later, and we have the car back (needed a couple of more parts on reassembly as they found a few bits of turbo in some of the hoses).
They didn't replace the cat, and there was no clouds of smoke coming from it, as I think most of the oil would have burned out during their test drive.

Anyway, the wife is happy & so is my bank balance.
New turbo, new intercooler and misc hoses, gaskets, etc and we only had to pay less than $400

Thanks again to John Hughes & VW :bowdown: