Now I understand


By Jim Taylor, Editor MACS ACtion Magazine

Perhaps you remember when cars had gauges: water temp, volts or amps, even oil pressure. That data was important for drivers because if any went to an extreme, either high or low, it could be a long walk home. But most of the gauges vanished over time due to cost and owner indifference.
I plainly remember complaints at the first shop I worked in that the customer’s ammeter would occasionally drop into negative territory “so there must be something wrong with the system.” Nothing anybody could say or do would convince the owner that this could be normal in some circumstances. Gradually, that message plus sufficient warranty claims stacked up at the factory and makers just quit putting certain gauges on the dash. What they can’t see can’t hurt.
Like most cars made in the late 20th Century, my wife’s previous runabout still had a temperature gauge in the instrument cluster. Her 1990s econobox had just the usual sweep-needle indicator, on a face marked from C to H without any numeric calibration. Variations on that theme have been in cars and trucks for decades.
Her little car ran happily for years with the needle somewhere in the center of the gauge. She knew to glance at it occasionally, and to disregard the minor, needle-width variations while driving. A little warmer or a little cooler?—as long as the pointer was near the center it was all good. That’s all she wanted to know.
And now, her next car – a 2010 subcompact – doesn’t have a gauge at all. “How do I know what it’s doing?” she asked. The only answer I had for her was “You have to trust the computer. It knows.”
In the new car, the temperature sensor(s) talk directly to the engine control unit, which politely turns on a little blue light in the cluster to remind the driver the engine is cold. Just drive gently ‘til certain conditions are met and the light goes out. No fuss, no muss and no excess information. In a worst case, a red warning light warns of an overheat—hopefully before its too late.
It took a little while, but my wife gradually accepted the concept of “no news is good news” for the car’s temperature and she doesn’t miss the gauge any more. Then she met “Susannah.”
In my June column, I mentioned that we recently bought a car that was delivered to us by Dr. Ben Pender, the wrench-turning subject of that column. The car is a 1960s British roadster, with a full set of gauges, all with real numbers. No “C to H” scale here.
The temp and oil pressure meters are “live” gauges with no electricity involved. The oil pressure gauge receives a fluid sample direct from the engine, and the temp signal is transferred via a sealed capillary tube with a thermal gas inside. Responses are quick and the driver can see what’s going on in short order.
During my early check-out drives, I had to relearn the art of “sweeping the gauges” periodically, but it came back quickly. (Don’t look for the number, just check the needle position.) On this car, the temperature gauge is on the right side of center and so, prior to our first joint outing in the car, I explained to my wife that it would be helpful if she could glance at the gauge occasionally for any sign of hijinks up front. I learned a lot after that.
Susannah’s engine has been rebuilt, makes good power and warms up quickly. The car is a joy to drive, and we were off on the first over-the-road outing. A quick 20 minutes on some back roads gave a good steady temp at 190 degrees. But sitting at a traffic light, I felt a sudden hand on my arm. “The temperature’s going up!” A quick glance showed it was about 200 degrees.
“Normal,” I said. “Hot idle and no airflow so it goes up a little.”
“But it’s not what it was. You said to warn you if it went up.”
“S’ok. Really. Only worry if it goes for top.” A few hundred yards past the light, the temp came back to its happy place, but the arm grab was repeated a few times in the next half-hour as the needle reflected engine load and airflow.
There was one particular note of panic when the pointer rose to almost 212 F going up a long hill at highway speeds. It was easy to sense her mental chain: 212 degrees equals boiling, that equals “boiling over” and that equals “the long walk home” plus “why did you ever buy this car?” No explanation of pressurized systems or changing engine load would suffice; to her, we were simply going to be on the side of the road.
Thankfully, that hasn’t happened, but other things have. After several recent outings, my wife is somewhat less jumpy with the inevitable fluctuations in the coolant temp—no arm grab in a while, but a couple of concerned looks. And I’m beginning to understand why many modern cars just have two warning lights. It’s not just cost cutting at the factory. For some, detailed or numeric information is just too much information. For them “OK” or “Not OK” is sufficient. Don’t tell them more than they need to know.

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When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.

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About macsworldwide

Mobile Air Conditioning Society (MACS) Worldwide Founded in 1981, MACS is the leading non-profit trade association for the mobile air conditioning, heating and engine cooling system segment of the automotive aftermarket. Since 1991, MACS has assisted more than 600,000 technicians to comply with the 1990 U.S. EPA Clean Air Act requirements for certification in refrigerant recovery and recycling to protect the environment. The Mobile Air Conditioning Society (MACS) Worldwide’s mission is clear and focused--as the recognized global authority on mobile air conditioning and heat transfer industry issues. www.macsw.org
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One Response to Now I understand

  1. John Hess says:

    Nice work, Jim. I will have Ellen give it a read for sure.

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