[s-cars] Re: [A4] A4 head rebuild, Part 6

[Igor Kessel]

PART 6 - cooling system woes.

*WARNING*
My notes below are NOT meant to be a substitute for not reading your
Bentley! They are only a supplement, ought to share some tricks and
hidden obstacles with you.

44. Install the remaining V-belt between the P/S pump and the water
pump. This paragraph requires some clarification. It had cost me an
extra day, a few extra parts and a LOT of aggravation. So read on.
Those who come from the 5 cylinder Audis are used to water pumps mounted
inside the engine block and driven by the toothed sprocket off the
timing belt. In the old 10v engines the water pump served as the timing
belt tensioner at the same time. W/o going into much detail I'll just
state that this approach was DUMB, the early water pumps were junk,
their thin 4mm O-rings were pathetic and they were the constant source
of frustration for us. By the time the old trusty 5 cylinder engine
entered its final 20v stage of life, the water pump had stopped serving
as the timing belt tensioner, although remained to be driven off the
timing belt. Which was by far the best approach.
In my 1998 A4 1.8T the water pump is mounted in a unique way for an
Audi. It has a totally separate housing and is mounted on the side of
the engine block. The thermostat is also no longer mounted inside the
engine block but is rather inside the water pump.
The water pump in the A4 with the AEB engine has a regular grooved
pulley comprised out of two clamshells. The P/S pump has an auxiliary
outer pulley. They are connected via the V-belt. Here's the fun part. I
looked for the belt tensioner to release the tension in order to bring
the two pulleys together for the new V-belt installation. There was
none! OK, what do we typically do in a case like that? You are right, we
put the belt around one pulley, drag it around the second pulley for as
far as it goes and then rotate the crankshaft with a rachet until the
V-belt jumps into position. So I did just that. After which I noticed
that the V-belt was loose. I mean seriously LOOSE as in I was able to
squeeze the belt with my fingers by at least 3cm on each side. I could
also rotate the water pump pulley by hand, inside the V-belt. I'd never
seen a new belt this loose, let alone I'd never seen a belt w/o a
tensioner.
OK, off to my office to read the Bentley. The Bentley sez basically:
there is no tensioner. WTF was Audi thinking designing this pump? It
turns out that the proper procedure was to put the V-belt onto the P/S
pump's pulley, then the first half of the pulley onto the water pump
shaft, then the belt, then put the second half of the pulley onto the
water pump shaft, insert the bolts and gradually screw the bolts in and
bring together both halves of the pulley thus squeezing the V-belt out,
hence tensioning it! Damn! I wish I knew that. It does pay to read your
Bentley beforehand, not afterwards. My thinking at that point was that I
had stretched the new belt effectively rendering it unusable. What an
idiot!

Since the car was all together and ready to get started I decided to see
if it would start and run after such a long head rebuild.
I turned the key and voila, the car had started at a 1/4 turn. I
connected the VAG-COM and began to monitor the first 4 channels, live. I
was mainly interested in the coolant temperature, the idle rpms, the
lambda and the timing.
In a few minutes the temperature had climbed to 90°C. I kept adding
coolant to the reservoir, checking the temperature of the upper and the
lower radiator hoses at the same time. The upper hose was getting
progressively hotter, while the lower remained to be cold. When the
temperature reached 115°C I shut the engine off fearing an overheat.
Something was seriously wrong. OK, back to the drawing board for me.

Naturally first suspect was the new thermostat. Out came the coolant,
and the thermostat housing. I took both the new and the old thermostats
to the kitchen and boiled them in a transparent Pyrex pot. Both started
to open at 90° and fully opened at 100°C, to the same stroke length of
~8mm. Just what the Bentley ordered.

I put the thermostat housing back, this time w/o the thermostat. Filled
the car with water with the garden hose. Started the car. The car idled
for ~15 minutes  and the temperature settled at ~50°C w/o going up. Both
the top and the bottom hoses had become equally warm to the touch. Which
meant that the new water pump had been working.

I ran out of possible explanations. I drained the water, put the
thermostat back in and refilled the system with coolant.

I summoned in my buddy who owns a 2001 A4 1.8T (not w/o my influence, I
must add humbly). Compared both idling cars in my garage, side by side.
Mine was still cold at the lower radiator hose. His was hot. OK, there
must be no coolant flow in mine.

At this point the only possible explanation was the loose new V-belt on
my water pump so that the open thermostat had created a serious flow
restriction. But since there is no tensioner whatsoever, what the hell
was the proper tension supposed to be in the first place?

I looked at my buddies's A4 engine in order to check what was his V-belt
tension as a benchmark for mine. To my surprise, his car didn't have
that V-belt. Hell, it didn't even have the water pump. WTF???

OK, back to my office, pulled up the Family Album on the screen. Aha,
the ATE engine (fly by wire variety) found in the later cars had a
totally different water pump. Just like in the old 5 cylinder engine it
was now mounted inside the engine block and driven by the timing belt.
Evidently at some point Audi had realised that they have screwed up the
water pump design in the early 1.8T and reverted it back to the old
trusty configuration. Good for them, but how am I supposed to know what
would've been the proper tension?

I decided to get the yet another new V-belt, coz I positively couldn't
think of anything else. A call to a local dealer next morning revealed
that the new belt was available for $15. I jumped in the car and
thankfully had enough common cense to grab my V-belt. The dealer's belt
was the same p/n 11x528 but had an Audi logo on it. Mine was aftermarket
made by Continental, also 11mm wide by 528mm long, p/n 11x528. I
compared the two at the parts counter. The new OEM Audi belt was
actually even slightly larger in circumference than my supposedly
stretched one. At that point I got really puzzled. But I bought the Audi
belt anyway.

When I looked at the Audi belt one more time at home I noticed that
although it bore the same number as my Continental, its trapezoidal
cross section appeared to be slightly larger. In addition, the teeth on
the Audi OEM belt were larger, whereas the Continental had the finer,
narrower teeth. It can't be THAT SIMPLE, thinks me.

I quickly put the new OEM belt onto both pulleys and started to squeeze
the clamshells together with the bolts just as the Bentley had
recommended. To my surprise the new thicker OEM belt had become pretty
tight and I could no longer squeeze it in my hands after I was done with
it. I started the car and within minutes the bottom radiator hose got
warmer and the car had finally settled at 94°C.

Who could have known! This has been the most non-trivial car puzzle in
my experience to date. Folks, please keep a note of this: in the '97-'99
A4 1.8T engine, code AEB, the water pump to P/S pump V-belt 11x528 HAS
TO BE OEM Audi!

45. I drained the cheap mineral motor oil that I had put in the engine a
few steps back. It had served its cleaning purpose and had to go. I
replaced the oil filter and filled up the engine with fresh Mobil-1
10W30 fully syntectic oil.
This had concluded the A4 head rebuild.

--
Igor Kessel
two turbo quattros