car problems

[franksolich]

They're all fixed now, and everything's in tip-top shape, but I'm still wondering.

The mechanic just dropped off the motor vehicle, and explained what had been repaired, information which I "heard." 

But then when I asked him how I could have diagnosed those problems, he explained details, but I wasn't "hearing" any more, and so grasped none of it.

Originally I just wanted an oil change, and made arrangements for that.

But a day and a half before the oil change, I noticed something peculiar about the brakes; it seemed that when one pressed the brake-pedal, one was shoving at air, air which was shoving back.

So I wanted that looked into.

About lunchtime, the mechanic, who is the most excellent automotive mechanic I've ever known, drove all the way out here to tell me there was another problem; the water pump was going.

So he changed the oil, replaced the rear brakes, and put in a new water-pump.

Now, I had successfully "diagnosed" there was a problem with the brakes, but had no idea about the water pump.

In fact, I'm rather aggravated at the temperature gauge.  On Sunday, the yellow SERVICE ENGINE SOON light came on.  I checked things out.  There's a plastic container where one puts surplus radiator fluid, and that was nearly--not quite empty, but nearly--empty.

Well, no big deal; it had been a rough winter, and the last time radiator fluid had been put in the radiator was.....September.  After I did that, the yellow SERVICE ENGINE SOON light never came back on again.

But how come when I was running low on radiator fluid, the temperature gauge didn't show a hotter-than-usual temperature?  Isn't this what temperature gauges are for?

On the water pump issue, as I mentioned, I asked him how one can tell there's a problem with it.  He said, "Well, it makes noise....." and then trailed off, remembering I wouldn't hear noise.

Then he said some other things about diagnosing a problem with the water pump, but I caught none of it, having been drained of physical and intellectual energy to "hear."

So the two questions:

(1) Why did the temperature gauge lie to me?

(2) How does one diagnose a problem with a water pump?

[Thor]

There is a weep hole on most water pumps. Radiator fluid will leak out of there if the pump  is going bad. Also, one can determine the shape of the bearing in the water pump by attempting to move the fan (belt driven only) If the fan wobbles at all, that means the bearing is probably going out in the water pump if the bolts on the fan are tight.

Finally, just because the reservoir is low doesn't mean it will overheat. There could have been enough fluid left in the rest of the cooling system to keep the temperature "normal", especially if you have been running the heater. Ideally, one should check their fluid levels at every gas up. At a MINIMUM, they should be checked at every oil change (~ 3000 mile intervals). Without a code reader, there's not really telling why the "Service Engine Soon" light came on for certain. However, there is a fluid level sensor in the coolant reservoir in most newer vehicles.

[RobJohnson]

Frank, it sounds like your mechanic really looks out for you. That is nice to see. Thor is giving you a great explanation.

Just because the water pump is going bad, does not always mean it has a leak. A loud water pump bearing is why many are changed. Furthermore, depending on if the engine is hot or cold will also play a part in the coolant level in the bottle.