Poor Fuel economy

The first thing I would do is check fuel pressure. Here is a link that shows how it is done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

As far as the thermostat, that can certainly play a role in the problem. Honestly, make sure you are getting a good brand. There are so many cheap things being shipped to us anymore.

Let me know what you find with pressure.

Joe

Wow. Those are both good parts. Could the fan clutch be locked and running full all the time?

Welcome back:

I have been stuck in Cleveland for the past week, and interestingly, I thought of your post last night. LOL I was wondering what you found. As far as engine temp, it should be between 195°F to 210°F. You are not too far off, but who knows. It may be enough to make a difference.

Here is some info you may find helpful. The attached pictures correlate with the directions. The link is a general description.

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

ENGINE COOLANT TEMPERATURE (ECT) SENSOR REPLACEMENT

REMOVAL PROCEDURE

NOTE: Use care when handling the coolant sensor. Damage to the coolant sensor will affect the operation of the fuel control system.

picture 1

1. Drain the cooling system to a level below the engine cooling temperature (ECT) sensor. Refer to Draining and Filling Cooling System in Cooling System.
2. Disconnect the ECT sensor electrical connector (1).

picture 2

3. Remove the ECT sensor.

NOTE: Replacement components must be the correct part number for the application. Components requiring the use of the thread locking compound, lubricants, corrosion inhibitors, or sealants are identified in the service procedure. Some replacement components may come with these coatings already applied. Do not use these coatings on components unless specified. These coatings can affect the final torque, which may affect the operation of the component. Use the correct torque specification when installing components in order to avoid damage.
Use care when handling the coolant sensor. Damage to the coolant sensor will affect the operation of the fuel control system.

picture 3

1. If installing the old sensor, coat the threads with sealant GM P/N 12346004 (Canadian P/N 10953480) or equivalent.

NOTE: Refer to Fastener Notice in Service Precautions See: Powertrain Management > Vehicle Damage Warnings > Fastener Notice.

2. Install the ECT sensor.

Tighten
Tighten the sensor to .........................................20 N.m (15 lb ft).

picture 4

3. Connect the ECT sensor electrical connector (1).
4. Refill the cooling. Refer to Draining and Filling Cooling System in Cooling System.

Let me know what you find out.

Take care,
Joe

Welcome back, Doug. You are very welcome. This has been a tough one, but I'm glad you feel a bit more comfortable with the outcome. I do, however, feel bad to hear how much was spent. I'm dealing with my own dilemma at this time. I followed the recommendations of repair manuals and my problem still exist. I now know what is wrong, but like you, to do it again will cost me money in a gasket, synthetic gear lube and at least another 4 hours of my life. Lol My father always told me, cars are the worst investment one will ever make. Well, nearly 35 years into this and I think I finally agree.

Please feel free to come back if you have questions in the future. Although it took longer to fix than I like, it was a pleasure helping.

Take care of yourself,
Joe

LOL. Honestly, this weekend I will have the time to once again take apart a differential. Not looking forward to it since I already did it once.

Regardless,

Take care,

Joe