The Case of the Red Hot Muffler

By Kyle Davenport

I had this 4×4 Ford Ranger in college that saw a lot of muddy hills and salty beaches. At one point, I had to replace the engine due to ocean water getting in the pistons.

One trip driving back to school at night, I started seeing the temp gauge slowly drop down to zero and then pop back to normal. I figured my thermostat was having a rough time and kept going. Then I noticed the oil pressure gauge was dropping too. I figured it was a strange electrical issue (I HAD neglected to ground the hood …) and kept going. Then I started noticing the engine would sporadically get really loud. I was on my third muffler after literally losing the first two, so I pulled over to check out my weld job. As I watched and listened to the muffler with the engine on, I started noticing that the muffler was glowing! I thought, OK, maybe it’s running lean and getting hot?

Then I thought about it. There is an electrical issue here, almost like a charge is building up in the motor, which would effectively raise the voltage level of the engine ground, and reduce the voltage across the temp and oil pressure sensors. Then possibly something happens and it releases the charge - through the muffler, creating the glowing I saw. I thought, an engine could be a capacitor - lots of metal plates separated by oil.

Then I thought about the strange sound, like it was missing. OK, if it’s missing, then unburned gas is going out the tail pipe, and getting burned in the muffler. Missing means the spark is not happening or is going somewhere besides the spark plug ….

Ah hah, the glowing in the muffler might be caused by the muffler being the ground for the spark plugs! Bingo - the motor is not grounded. Sure enough, I had neglected to connect the big ground strap to the motor. Without any tools, I yanked my beloved subwoofer’s wires out and wrapped them all over the battery and motor.

It ran great after that.

Kyle Davenport is currently living in Santa Cruz and working at Easton Bell Sports managing product compliance. He previously worked at WET Design (creators of the Bellagio water feature in Las Vegas), Plantronics, and two semi-conductor industry companies. He received a BS in Mechanical Engineering from Cal Poly San Luis Obispo, and also took 200 units in industrial engineering there. He built his own circuit boards when he was 12 and still has a love for mecha-tronics, but he hasn’t figured out how to make that a profitable career in his beloved hometown.