Tech Tip No. 7
Originally published in the quattro quarterly
SQUEAL FROM BACK OF TURBO ENGINE
Sometimes there is an annoying squeal coming from the back of the turbo engine. I've had the pilot bearing changed. I've replaced the starter. I've
replaced the throwout bearing. Nothing has seemed to fix it.
This is an insidious one. Try this: Drive forward several
feet and then hit the brakes hard. Listen for the squeal. Drive in reverse several feet and hit the brakes hard again. Listen for the squeal. The squeal may stop temporarily with either of the maneuvers.
Now try this: With the engine running and the squeal present
gradually pull the oil dip stick out. When the engine just about quits quickly push it back. The squeal should change in pitch and perhaps stop temporarily. If that doesn't quite make it go away open and close the
oil filler cap quickly without killing the engine.
Have you figured it out yet?
The squeal is coming from the rear engine main seal! Using the
brakes in the manner above moves the crankshaft forward and back ever so slightly. The seal changes its position relative to the shaft and reseats itself.
What causes it in the first place? It is the fact that the engine
crank case is attached to the intake manifold system and places the seal under a vacuum condition. It is designed to keep the oil in not the air out. The original seal is old and has hardened. The sound you hear is
the air being sucked past the seal. When you pull out the oil dip stick the vacuum is released and the squeal stops.
To fix the problem replace the rear main seal. Suggestion: If the
transmission is ever removed for another reason replace the rear main seal at that time.