'89 200 tq - disappearing coolant & after run control unit

[Doyt W. Echelberger]

Those invisible leaks are nasty things to sort out. I have lost coolant to
invisible leaks in several ways with my 87 5ktq. Each case involved the
coolant streaking back along hot surfaces that caused the fluid to
evaporate rather than pooling under the car, and each leak also only
happened when the engine was turning the water pump:

VARIOUS MAIN COOLANT HOSES: Upper rad, lower rad, heater in and out. Look
at the upper rad hose and make sure you didn't nick it in replacing the new
aux coolant pump hose. Also, check the upper rad hose connections.

COOLANT RESERVOIR: The coolant reservoir on my car is the first thing that
the stream of heated air hits as it departs the rad fan. A tiny crack
developed in the upper center of the face that gets the heated air. I had
to replace the coolant reservoir.

TURBO SUPPLY LINE: The turbo gets coolant from a small supply line that
exits from the cylinder head fitting that also supplies the upper rad hose,
in the region of the first-second spark plugs. This inconspicuous line,
about the diameter of a pencil, runs forward and curves off toward the
turbo, around the front of the engine. It has a short rubber section near
its cylinder head origin, and this is covered with a fabric sleeve. The
rubber had a pin hole leak. Beastly thing to find and replace.

HEATER CORE: The heater core developed some seepage that never showed up.
Replaced the heater core.

HEATER CONTROL VALVE: The plastic heater control valve near the distributor
cracked and leaked. Replaced it with a metal valve from Advanced
Auto...about $6.

RAD NECK: The plastic neck of my upper radiator hose connection cracked,
and leaked before it finally broke off and dumped all my coolant. That was
this weekend. Car is inn shop, getting rad replaced.

WATER PUMP: Water pump began failing and leaked coolant back along the
engine. This went on for several months until the pump finally failed
enough to show coolant drips when I back-filled the system through the
small hose that feeds the coolant reservoir. I put a funnel in the hose,
after disconnecting it from the coolant reservoir, and this somehow
supplied water to the water pump, and it ran out in a small stream that I
could see.

AUX WATER PUMP HOSE: Finally, just like yours, my auxiliary water pump that
cools the turbo developed a hose leak near its supply point at the
radiator. Replaced the complicated molded hose.

That about covers my coolant leaks. The leaking water pump scared me the
most, because I though I had a leaking head gasket. But my mechanic said he
had never seen an Audi 5 cylinder with a leaking head gasket in all the
years he has worked on them. He drives on just like mine. So, we looked at
other causes and found one.

Best of luck.

Doyt Echelberger
Ohio   USA





 >>>>>>>>>>>>>>>>>>>
At 07:27 AM 7/21/2003 -0600, you wrote:
>I just replaced a failed and leaking Aux. pump. No visible signs of
>leaking coolant now, yet a cup or two disappears after each drive. The
>new aux. pump still isn't running and I have tracked it to a weak ground
>(pin 1) which goes to the after run control unit. Are these control
>units a failure mode? Or, should I look to the ground welded in the
>right engine harness? I did get an intermittent buzz/click from the
>driver's side foot well.
>
>Are these related? Where is the coolant going?
>
>Bruce