My truck is showing it is overheating. I have replaced thermostat, radiator cap, checked hoses, and still it is showing overheating over 210. I was told that it could be the temperature sending unit, can anyone help? Thanks
To confirm if your engine is overheating or if it is an instrument gage; then have someone put a scanner on the car to monitor the engine temperature.
The engine has a temperature sensor for the coolant and one for the computer. If the sender or gage is functioning properly then the reading for the computer sensor will measure the same.
When the car is not moving the cooling fans should come on at about 220 degrees. If the engine is running at 210 degrees it may not be hot enough to turn the fans on. This could be a normal condition.
If you are running the car at highway speeds then you may have another problem, your engine may be air bound.
Jack the front of the car up and put it on jack stands or if you have ramps you can use them. With the engine cool take the radiator cap off and start the engine and let it run until the thermostat opens up. Keep filling the radiator until it won't take anymore antifreeze. Then put the cap on and road test the car to see if the condition improves, you may have to do this a few times to get all the air out.
On most cars the engine sits lower than the radiator and air gets trapped in the engine after changing a thermostat. Raising the front of the car will help move the air pocket to the radiator and out of the system.
Let me know if this information was helpful.
Thank you for the information. We didn't jack the truck up. We changed the thermostat again, fans come on, its not the water pump, but it still went to overheating. We didn't know about jacking up the truck. Wow. Thanks. I will mention this to my helper. Again thank you so much. Thought maybe it might be the engine cooling sensor, but not sure. Roxxy
Oh also its not a car its a 1996 GMC Sierra 4XS with a 5.7 engine so I don't know if I would jack the truck up too. Let me know if I should OK? Thanks. Roxxy
If it's still overheating then you should try it, the engine still could be air bound. You need to try this procedure so you can eliminate it from the diagnostics.
Let me know how you make out.
Fill the radiator, let sit until no bubbles come up. Remove the belt that drives water pump. Start the engine. If it starts bubbling its the head gasket or cracked head or cylinder wall.
Started overheating at 60,000 miles nothing had been done to it. Changed thermostats, sender, fan clutch, instrument panel was showing 50 degrees hotter than scanner, fan shroud. Filled block up to bottom of thermostats and installed them. Coolant amount matched amount drained out and had never lost any out of the overflow. System holds pressure and cap holds correct pressure and releases at correct pressure.
At that mileage it is possible a head gasket could be going bad causing the engine cooling system to get air bound.
You usually don't lose coolant but compression from a cylinder can leak past the gasket and form an air pocket in the head and intake manifold. This air pocket can let the engine temperature creep up slowly the bigger the air pocket gets.
Tech1diesal wrote: fill the radiator, let sit until no bubbles come up. Remove the belt that drives the water pump. Start the engine, if it starts bubbling it's the head gasket, cracked head or cylinder wall.
You can also try to raise the front of the truck so the radiator is higher than the engine, you can use jack stands or ramps either are good. With the engine cold remove the radiator cap and start the engine. Let the engine heat up, as it heats up you will probably see the coolant level go down in the radiator. Keep filling gradually until you don't have to add coolant anymore. This could take some time so be patient. Replace the radiator cap and test drive the truck and see if the overheating goes away.
If it comes back then it appears that it might be the head gasket, cracked head or cracked block at the worst.
Let us know how you make out.