Engine temperature and mileage in a chev 4.3

I have a van with a chev 4.3. Great runner but in the last two years as the outside temperature has dropped so has my mileage. I have replaced the thermostat and recently have had a mechanic put a scan tool on it and it reads 198, and use a infrared temp sensor on the thermostat housing which also reads 198. however the temp gauge on the dash reads at about 1/3 where it use to run about 1/2+. Since my mileage drops almost by half I am seriously looking for a cure

What temperature thermostat was installed?


Perhaps the temp sensor is bad: the engine is at the right temp but the computer is getting bogus information.

The coolant temp signal definitly can affect fuel mileage but I must ask have you skipped over more likely causes of poor mileage? A drop of 50% is drastic, have you pulled the plugs and given them a read? is there black soot on the body panel around the exhaust? Is this a Central Port Injection 4.3? not my favorite for mileage.

When you say the temp gauge on the dash reads about 1/3 where it used to run at 1/2 plus, do you mean that it used to run at 1/2+ during previous winters, or that it ran at 1/2+ during the summer?

tester 198

Okay. Check and see if the fan clutch for the radiator fan is bound up. With the engine cold open the hood and try spinning the fan by hand. The fan should spin freely. If it doesn’t the fan clutch is bound up and stripping the heat from the radiator.


I will look into the spark plug idea. I would think however that as soon as the engine got up to running temp that the milage would recover. It is throttle body injection, and it seems odd to me that the Astros I have driven since as well as the two my brother has owned have all gotten a consistent 15mpg

You said, “I would think however that as soon as the engine got up to running temp that the mileage would recover.” The engine computer is getting the same temperature as the dash gauge. The engine computer won’t go into active controlling, which is where the best fuel mileage results, until the engine coolant temperature SIGNAL goes past 160F degrees. Your engine temperature SIGNAL doesn’t hack it.

I may not have communicated very well. According to the scan tool the computer was reading 198* as was the inferred thermometer. It was only the temp gauge on the dash that read in the 1/3+ range as opposed to the usual 1/2+ of the past.