AHF turbine contacting housing at low altitudes?

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VAG Fan
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Posts: 1440
Registered for: 8 years
Location: Pretoria

AHF turbine contacting housing at low altitudes?

Post by VAG Fan »

I travelled to KZN this weekend.

My AHF's turbo is in need of an overhaul, as the VNT mechanism forever becomes sticky. I have a new turbo already, just haven't come around to fitting it, so that I can open and service the old one.

I free the VNT mechanism manually from time to time, and then it operates normally for a while. If it becomes sticky, I get overboost resulting in limp mode. I freed the mechanism thoroughly before the trip.

A funny thing happened in KZN on the second morning (Hillcrest area, about 500-700 m above sea level). Going up steeper inclines, with moderate revs and boost, I could hear a mechanical, grinding nose from the turbo. I can only think that the turbine was contacting the housing.

So I disconnected the vacuum hose from the actuator, closed the open vacuum port on the N75 and continued with the VNT basically in "open" position. This (together with very gentle driving up the mountain passes and 110 km/h max) got me back to Pretoria with no more noises.

When I reconnected the VNT's vacuum hose at home, to try and listen to the noise again, it is now completely gone! The turbo is once again running, boosting and wooshing normally. Oil usage over the trip wasn't excessive either (perhaps 100 ml over 1400 km). That's normal, as I normally top up 1 L mid-way between 15000 km service intervals.

I'm quite puzzled by the grinding noise under boost that suddenly appeared but has now disappeared. And I really have no idea how urgent it is to exchange my turbos. Can anyone relate something similar?

I would actually expect that the Reef puts MORE strain on the turbo, not the coast...
Mark R.
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2004 VW Golf TDI, type 1J, AHF, 317k (2016-current) --- daily
1990 VW Fox, type 16, HM, 304k (2005-current) --- spare runaround
Previous:
1992 Audi 500 SE, type C4, AAR (2001-2020) --- nice while it lasted
1983 VW Golf GTS, type 17, FR (1992-2005) --- most fun car I've ever had
1978 Audi 100 GLS 5E, type 43, WC (1991-92) --- died in the side of a Rekord who cut me off
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