Hey Rob, I may have you beat as I have been working on trucks just under 50 years. Usually I will drill a smaller hole if needed. The thermostat in the earlier picture is going in my 64 year old 1956 3800. I don't want it to clog with rust.
The parts guy was trying to sell me 180 degree stat but I did find the 160 degree. I am pretty sure this larger hole will not effect the check engine light.
Some more expensive truck thermostats with a very small bleed hole have a ****** berry in the hole to make sure it does not clog.
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So I have a question that anyone can answer. The first correct answer, with an explanation of why, will win the prize.
What may happen on warm summer day if your truck has no thermostat installed? This may even happen on a cooler day.