Beck TD, Part 81: Testing the Temperature

 This was an interesting bit of garage science today. About a year ago, I replaced the water temperature gauge in Beck TD's dashboard because the existing one had failed. I was suspicious of the new gauge right away, because it seemed to read about 10 degrees hotter than the old one, and also would read 10 degrees hotter than the temperature indicated on my laser non-contact thermometer, checking right at the gauge sender.

I had read of a test for those capillary-style gauges using boiling water, but I had never tried it. Until today, that is! Read on for the interesting results.

I had a second gauge that I trusted, so I began by validating it. Here's the setup I used - a pot of water heated by a small propane burner.

It took a surprisingly short time to bring the water to a rolling boil.

Gratifyingly, the gauge read 212 degrees Fahrenheit, exactly the boiling point of water. It was good indeed!

I had previously extricated the sender for the gauge in the car, and routed it to the side. That allowed me to move the pot of hot water to the floor by the car. I could compare the gauge I just tested as "good" against the one in the car. 

I fully expected the gauge in the dashboard to read 10 degrees higher, but was surprised to find the readings essentially identical at 190 degrees. Hmmmm....

All came clear as I let the water cool further. You can see here that my laser non-contact thermometer says the temperature was now about 153 degrees.

Comparing the two gauges, the "good" gauge read about 155 degrees, while the one in the dash still read 180. Ah-HA! My method of testing previously was to return to the Grant Street Garage, test at the engine with the laser, and compare. The dash gauge was always higher, but that was not because it was reading higher, but that it was slower to show a cooler temperature on the way down. That also explains why, once the car got hotter at a traffic signal, the temperature stubbornly stayed higher, even after moving and getting some airflow over the radiator.

I decided to bite the bullet and swap the gauges. The most onerous part of that was rewiring for the different style of light bulb in the good gauge. 

This was easy-peasy compared to most of my blog posts, but I'm glad I went to the trouble. I'm doing some work right now in changing my cooling system, and having a verified gauge to track results adds to my confidence level.

Continue on to Part 82....