Coolant sensor/ possible cooling issue/code P1299

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bar422

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This is kind of related to a previous post I had........For some reason my 2001 XLT temp gauge in the dash all of the sudden went all the way to the hot side and my coolant light came on while I was driving one day. I stopped, shut it off and checked and there was no overheating at all and no coolant coming out anywhere....no sign of an overheat at all. I shut my truck off for about 5-10 seconds and restarted it and the gauge then had dropped quite a bit and the coolant light went off. I continued to drive and then it happened again about 10-15 minutes later......I checked everything again and nothing. Shut the key off again and restarted then the light went off and sensor had dropped again. This continued on/off for several weeks then one time it did it and the check engine light came on and went into "safe mode " where the truck would still run but would go very slow. I was able to get the code read and it was P1299. I got the cylinder head temp sensor changed (CHTS) the same day but the problem came back the next day. The truck has never actually overheated.....just indicating that it was. Obviously coolant doesn't cool off in 5-10 seconds so I would have thought it was the sensor. I did notice that after replacing the sensor and it starting acting up again that turning the key on /off didn't drop the temp gauge anymore (it did drop after leaving it set for awhile). It seems like the longer you drive it the more likely it will happen although it doesn't happen everytime ( I even left it running in my driveway for an hour after driving it and it didn't do it ). Has anyone had this issue or have an idea what or where to look next? Any help would be appreciated.
 

stamp11127

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As bedrck said, coolant level, bleed air from system, could also be a failing water pump.
What kind of coolant are you using? If you don't know, what color is it?
 
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bar422

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The truck has been sitting for bout 2-2.5 hours now and the level is about 1 -1.5 inches under the cold mark on the tank. The coolant is green (brownish green now). I had the cooling system completely flushed approx. a year or year and a half ago. Any more input would be great!
 
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bar422

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Could the kind of coolant in the truck cause this?
 

stamp11127

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No, the different colors represent the different mixtures. Is the brown color oil, leak fix or rust?
 

IMINYOURCHAIR

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the level is about 1 -1.5 inches under the cold mark on the tank.

go ahead and fill the tank up to about full. if it is low it will need to be that full to draw more in and push the air out. in my experience the air tends to pool in the upper rad hose so give it a squeeze after you fill it up.
 
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bar422

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As far as the color goes I assume it is rust......nothing has been done since it was flushed and there were no leaks as far as I know (I wonder if it needs to be flushed again?). The only reason I had the system flushed out before was because it wasn't heating very well. I did fill it up to the proper cold level and drove it today and it didn't act up at all. I'm thinking about doing the thermostat just because I have never done it since I have had it. I may add more coolant just in case it is the air in the upper hose too. Anymore input would be great and thanks for the responses so far!
 
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