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Thread: Oil leak at rear of engine annd boost leak. TT 8N 1.8 Quattro

  1. #1

    Default Oil leak at rear of engine annd boost leak. TT 8N 1.8 Quattro

    Hi everyone,
    some vaguely similar threads around but nothing that seems to cover this specifically.
    During a 5 lap session on the track I started hearing a honking/whistling sound when boosting hard. Iíve heard this before and it was an easy fix tightening up the hose clamp on the blower outlet. After my first track day I found every nearly hose clamp on the boost air system was loose. This time Iím pretty sure it is just the big one on the TC outlet, judging by the distinctive sound but too hot to check as yet.
    First question: why does this boost leak keep recurring? Is it possible the engine is over- boosting? Boost pressure logged at 25 psi on the highest peaks.
    After the next session I saw a whisp of white-ish smoke from the rear of the engine, coming up under the lagging of the TC pipes. During subsequent sessions, more and more smoke observed. Some dirty oil observed on hoses below TC and some very clean oil on gearbox and transaxle housings below TC. No obvious oil leaks from rocker cover or anywhere else.
    Next question: could this oil all be coming out of the boost air system via a leak?
    Seems like a lot of oil to be in the air system but I guess really only a few mils of oil altogether.
    TC was renewed at 120,000km, now at 165,000km, so hopefully TC oil seals ok. Valve guides and complete top end rebuild about 30,000 km ago. No smoke in exhaust. Oil consumption very low, maybe 0.25 litres in the last 6,000km.
    Next question: what is a ďnormalĒ amount of oil in boost system.
    Last question: systematic way to troubleshoot?
    Any and all advice much appreciated.

  2. #2


    Hi All,
    Iíve renewed the N75 (oem), N249 and diverter valve. Thoroughly checked all hoses and clamps visually (but not smoke/leak tested).
    Iíve put a bicycle pump on the waste-gate actuator line and verified that it opens somewhere around 5 - 10 psi (hard to tell exact pressure as the gauge is not of a suitable scale). I can move the waste-gate linkage very easily by hand but Iíve read that it should be a bit harder(?).

    In first and second Iím now getting boost peaks around 35 psi (and often blowing the hose off TC outlet).
    On a long push in 3rd, boost settles nicely at 15 psi. On two occasions near the top of the rev range, say 5000 to 5500 rpm, car seemed to go in to safe/limp mode and boost dropped to 5-6 psi.
    Iím thinking wastegate actuator might be too slow to regulate boost in the short term (e.g. 1st and 2nd). Possible leaky diaphragm on the actuator.
    Also, possibly ECU needs reset by battery disconnection.
    Anyone have any diagnosis that fits these symptoms? Any ideas for further tests and checks to identify the problem?

    Iím using an Bluetooth OBDlink MX+ and itís app to get and log data. It only updates once a second and doesnít get all the data I need (e.g. boost demand). Anyone know of software I can use with this and iPad to get more data channels and better frequency of data?

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