Coolant Loss, Water Pump or Head Gasket.

My W124 M102 ('92, 100k miles) is losing coolant, about an inch every
two
weeks or so in the reservoir. Replaced a couple of hoses that were
dripping a bit,
and the reservoir cap. Now there is no visible exterior leaks from the
system.
Also changed coolant and flushed the system, including the heater
core. Still losing.

In addition, I've noticed that the loss is greater when the car has
been
running in stop and go traffic, at 100 - 110 ºC. There is almost no
loss
during highway trips with the Tº steadily at 80 ºC.

My last hope before start thinking about head gasket is that the loss
is from
the water pump bearing. The car has a clicking noise coming from the
belt area
when starting cold in the morning, which disappears completely after a
minute.

I tried a mechanic's stethoscope on the pump, but the test wasn´t
conclusive,
the alternator's bearing could be the noisy one.

Aside from the coolant loss the car is almost perfect. It has good
power (for
a 4 cyl.), idles smoothly, no oil or fuel in coolant, no coolant in
oil, and
no white smoke from the exhaust. Also, all the spark plugs look fine,
with a normal
brown color.

Is there a better way to diagnose the pump? Should I change the pump
and see?

Please advice.

Thanks
MMansilla

On 16 May 2007 11:09:18 -0700, marcelomansilla (AT) 123 (DOT) cl wrote:

My W124 M102 ('92, 100k miles) is losing coolant, about an inch every
two
weeks or so in the reservoir. Replaced a couple of hoses that were
dripping a bit,
and the reservoir cap. Now there is no visible exterior leaks from the
system.
Also changed coolant and flushed the system, including the heater
core. Still losing.

In addition, I've noticed that the loss is greater when the car has
been
running in stop and go traffic, at 100 - 110 ºC. There is almost no
loss
during highway trips with the Tº steadily at 80 ºC.

My last hope before start thinking about head gasket is that the loss
is from
the water pump bearing. The car has a clicking noise coming from the
belt area
when starting cold in the morning, which disappears completely after a
minute.

I tried a mechanic's stethoscope on the pump, but the test wasn´t
conclusive,
the alternator's bearing could be the noisy one.

Aside from the coolant loss the car is almost perfect. It has good
power (for
a 4 cyl.), idles smoothly, no oil or fuel in coolant, no coolant in
oil, and
no white smoke from the exhaust. Also, all the spark plugs look fine,
with a normal
brown color.

Is there a better way to diagnose the pump? Should I change the pump
and see?

Please advice.

Thanks
MMansilla
I had the same problem on a XJS Jag . It was the head gasket. It shows

on a compression test and white smoke on the exhaust.
j

I have a Rear Wheel Drive 1985 Toyota Corolla GTS Coupe that has the
same type of invisible slow coolant leak. It's been steady for 15
years. I want to get it fixed, but I can't find the source of the
leak. It is my understanding that coolant leaks into the cylinders
will foul your oxygen sensor. My O2 sensors seem to last normally, I
just replaced one a few thousand miles back, only the second time I
have replaced an O2 sensor in 22 years and 260,000 miles.

But I am suspecting that it is a head gasket problem. I am
speculating that it is a hairline crack in the gasket that leaks to
the outside air. I was in Mammoth Lakes yesterday and there are a few
stoplights there. I wound the car up from one light and then just as
I was speeding along, the next light turned red. I jammed on the
brakes, and I could smell coolant as the air I had left behind in my
wake caught up to my open windows. Apparently the leak of coolant
increases with RPMs.

I am probably going to take the head off later this year and get it
rebuilt. The valve springs are probably a little tired anyway,
although it will wind up to its red line of 7300 RPMs with no
problem. This car has a dual overhead cam 16 valve engine. It goes
like hell and with RWD and LSD powerdrifts really nice.

I also have a 1982 Mercedes 300 TDT I have had for a long time.

Paul Fretheim

On May 16, 11:09 am, marcelomansi... (AT) 123 (DOT) cl wrote:

My W124 M102 ('92, 100k miles) is losing coolant, about an inch every
two
weeks or so in the reservoir. Replaced a couple of hoses that were
dripping a bit,
and the reservoir cap. Now there is no visible exterior leaks from the
system.
Also changed coolant and flushed the system, including the heater
core. Still losing.

In addition, I've noticed that the loss is greater when the car has
been
running in stop and go traffic, at 100 - 110 ºC. There is almost no
loss
during highway trips with the Tº steadily at 80 ºC.

My last hope before start thinking about head gasket is that the loss
is from
the water pump bearing. The car has a clicking noise coming from the
belt area
when starting cold in the morning, which disappears completely after a
minute.

I tried a mechanic's stethoscope on the pump, but the test wasn´t
conclusive,
the alternator's bearing could be the noisy one.

Aside from the coolant loss the car is almost perfect. It has good
power (for
a 4 cyl.), idles smoothly, no oil or fuel in coolant, no coolant in
oil, and
no white smoke from the exhaust. Also, all the spark plugs look fine,
with a normal
brown color.

Is there a better way to diagnose the pump? Should I change the pump
and see?

Please advice.

Thanks
MMansilla

The pressure in the cooling system is greatest after shut down of a hot
engine. On a warm day shut it down and after say 15 or 20 minutes
carefully inspect the waterpump (and radiator as another suspect) for a
leak. This is a process of elimination so start with the easiest and
cheapest components i.e. waterpump vs. the cylinder head or its gasket.
--
© 2007 T.G.Lambach. Publication in any form requires prior written
permission.

marcelomansilla (AT) 123 (DOT) cl wrote:

My W124 M102 ('92, 100k miles) is losing coolant, about an inch every
two
weeks or so in the reservoir. Replaced a couple of hoses that were
dripping a bit,
and the reservoir cap. Now there is no visible exterior leaks from the
system.
Also changed coolant and flushed the system, including the heater
core. Still losing.

In addition, I've noticed that the loss is greater when the car has
been
running in stop and go traffic, at 100 - 110 ºC. There is almost no
loss
during highway trips with the Tº steadily at 80 ºC.

My last hope before start thinking about head gasket is that the loss
is from
the water pump bearing. The car has a clicking noise coming from the
belt area
when starting cold in the morning, which disappears completely after a
minute.

I tried a mechanic's stethoscope on the pump, but the test wasn´t
conclusive,
the alternator's bearing could be the noisy one.

Aside from the coolant loss the car is almost perfect. It has good
power (for
a 4 cyl.), idles smoothly, no oil or fuel in coolant, no coolant in
oil, and
no white smoke from the exhaust. Also, all the spark plugs look fine,
with a normal
brown color.

Is there a better way to diagnose the pump? Should I change the pump
and see?

Please advice.

Thanks
MMansilla

I have a test I use to see if the head gasket is bad. Begin with a cold

engine and open the radiator cap. Start the engine and look into the
radiator. If the head gasket is leaking you will see air bubbles rising
in the radiator. Other checks that have been mentioned are to check the
compression and check the exhaust for white smoke. If one cylinder is
low in pressure then there could be a head gasket problem. If two
adjacent cylinders are low in pressure, then almost certainly there is a
head gasket problem.
HTH
EJ in NJ

There it was, coolant leaking from the bottom of one of the
radiator's plastic sides, hot engine.

Thanks