odd temperature readings

My engine temp barely reads above the bottom of the guage after a five or so mile drive. Once the truck is shut off after the drive and then key is turned to the on position, the temp will read about a quarter of the way up and upon start up, will decrease back to the lower reading. I'm thinking something might be up with either the thermostat or the temp sending unit.Opinions and insight will be much appreciated. Thanks!

 

I would run a ScanGauge to find out what the real temp is. The factory temp gauge is not vary accurate.

Do you have good heat? If not, you could have low coolant level, this could be why you dont get a good reading on the gauge.

 

Sounds like the thermostat is stuck open. They are cheap to buy, I am not so sure on the change out on the 4 banger.

 

Heat is good and comes in a timely manner. And coolant is full. I'm Getting the impression that it might be a faulty guage.

 

Or temp sensor.

 

I would think stuck open thermostat or faulty sensor. It would be a rarity that the gauge would be faulty.

 

Sounds like an electrical ground problem.

 

The first reply is correct. Just get a scan gauge to read the data (coolant temperature) while the engine is running. There is a temperature sensor for the computer and another for the instrument cluster gauge. So just compare the two. Some auto parts stores will hook up a scan gauge for you to check for free.

The coolant could be at 140F and the heater would still feel warm, so you can't judge if your thermostat is good from that.

How long since the last coolant/thermostat change? If it's been more than 2 years it would be a good idea to change it since the coolant loses its corrosion prevention ability over time.