It has been fine since I last replaced everything and flushed it. This just started happening yesterday.

 

Yeah, that sounds like air to me.

Check coolant level. Bleed the system. Did you check the fan?

I'd be wary driving it without this problem being solved. Don't want to ruin an engine, heads, head gasket

 

And could also be bad connection between engine coolant temp (ECT) sensor and ECU. From RAVE:

If the engine coolant temperature gauge receives no input or the input is out of range the

temperature gauge will read cold and the high coolant temperature warning lamp will be illuminated.

Coolant sensor is between AC compressor and alternator on top of motor. Check connector and wiring. If a scanner is attached, temp should read ambient when first cranked in morning, not -40F, etc.

 

Just wondering how air would get in the system all of a sudden. Has been fine after my coolant flush and bleed like 6 months ago.

Seeing that it was over heating on the highway doing like 80 Mph I am sure the fan wouldn't be doing much in any case.

When the light came on this morning the engine has only been runing for about a minute or 2. I would think that it wouldn't even be warmed up enough to over heat.

What are signs of a bad water pump? What are signs of a bad radiator?

 

I am going to check this thanks. There is no steam or anything, and if it looks overheated and the light is on, if you turn it off and on again, I believe it just seems to reset. It will come back on with a neutral temperature.

 

could be a bad sensor, could also be a dry sensor. The temp. gauge only works if its sitting in coolant.

 

I have just ordered a coolant temperature sensor because it does seem like it could be faulty as it seems weird that it's so erratic all of a sudden. The fact that the light was telling me it was over heated after being on for a minute or two, and the fact that it resets it self by cycling the ignition makes it seem more likely a sensor.

I am all up for other ideas, and input, and I greatly appreciate all your help, and will let you know the outcome for future reference.

 

Do I have to take anything off to get to it? Should it be straight forward?

 

That is an important point, becuase if there is a steam pocket inside, it is a lot cooler in the steam than in the hot water. Don't try it at home with pasta on the stove.

As for bad WP, frequently they begin to leak out the nose, and/or wobble the pulley. Flow testing is iffy, they produce 2.64 gallons per minute flow at 1000 rpm. As for radiator, clogs seem to take place on the lower rows due to settling of crud and Dexmud (dexcool sludge), the lower rows close off, and are much cooler (by 10F or more) from the top rows. Feel fins by hand or use IR thermometer.

Pix of worn out WP, aftermarket WP with larger bronze impeller, dexmud in radiator.

Based on just observations of the temp gauge, you can crawl up in temp over time, while computer driven gauge stays at 50% over a very wide range. One day, your temps are no longer in the "good" range, so they pop up. With scanner or Ultra Gauge you could have seen this coming.

 

The interesting part is everything was acting 100% normal just until yesterday. Never saw any sort of issues that would have been a precursor to this. At the most the temp gauge would be at 50% after some driving around, and there was never any leaking, squeaking, noises or anything.