Hi, I have a 1986 Monte Carlo LS 4.3 FI V6, 110,000 mi, and just recently in the past few days my temperature light (an idiot light not a gauge) has been flickering on and off. I had my thermostat checked and it was open but we took it out just in case it wasnt opening all the way. But the light is still coming on. There are a couple ideas as to whether it's the fan clutch, or whether or not the wiring to the light is maybe touching the exaust manifold and grounding out. Its running fine when I drive it Ive been checking under the hood when I stop and there is no steam coming from it. So I'd like to hear any suggestions anyone has. Thanks.
NEVER_NEVER take a thermostat out of a modern engine. It will not allow the computer components to work properly. That engine is designed to operate at 200 degrees F. It will also cause the water to flow through the engine too fast not allowing it to cool the engine. It waill also ruin you heater core with full water pump flow.
Now that we are over that, have the radiator checked, I supect your radiator is not flowing right. It is a common GM failure especially if the coolant hasn't been changed as required.
It on the off chance could be a defective sending unit. Put your T-stat back in and change the sending unit, it is right by the T-stat housing and has one wire. Inexpensive repair. If it continues have the rad fixed. Good luck