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 C. There is almost no loss during highway trips with the T steadily at 80 C.
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 wasnt 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
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On 16 May 2007 11:09:18 -0700, snipped-for-privacy@123.cl wrote:

on a compression test and white smoke on the exhaust. j
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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, snipped-for-privacy@123.cl wrote:

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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.
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There it was, coolant leaking from the bottom of one of the radiator's plastic sides, hot engine.
Thanks
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snipped-for-privacy@123.cl wrote:

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
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