Cylinder head temp probes surprised me on a 2021 rebuild

I pulled a head off a 2021 Freightliner that had a burnt valve at 310,000 miles. The owner swore it was fuel quality, but I found the coolant temp sensor was reading 20 degrees low for months. That meant the ECM never derated power when it should have. A $90 temperature probe kit from NAPA showed the real numbers in 15 minutes of highway testing. I checked three other trucks in the same fleet and two of them had the same sensor drift. How many of you actually verify sensor accuracy on every rebuild, or do you trust the computer readout until something fails?

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thomasb244d ago

Man, this hits home! I ran into the same deal on a couple of RAM Cummins trucks a few years back, temp sensor was off and the computer never knew anything was wrong until the head gasket let go. What worked for me was grabbing an infrared temp gun and shooting the thermostat housing and upper hose after a good hard run, then comparing that to what the scan tool said. Takes five minutes and you catch the drift before it eats a valve or worse. If the numbers don't match within a few degrees, I just swap the sensor, they're cheap and it saves a ton of grief down the road.

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