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1999 Deville Concours
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Discussion Starter #1
I have been having overheating problems on 99 deville concours. Upper hose gets hard and very hot to the touch. Fans not kicking on. Brand new thermostat but it is not reading hot. It stays in the middle even when I am clearly running hot. Replaced the temperature sensor also.Possible air block? It seems like my coolant is not circulating. Any ideas?
 

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Re: Please Someone Help!

Upper hose is supposed to get hard and hot. How are you diagnosing that it is overheating? Fans do not kick on until the coolant temp hits 224F.
 

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98 DeVille, 97 DeVille d'Elegance
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Re: Please Someone Help!

like maeng9981 said the fans don't come on LOW until 224.
Turn the AC on the fans should run on LOW all the time if not check fan fuses/relays(they are between fans down low).
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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What are the signs of "clearly running hot" ? Losing coolant, coolant blowing out the surge tank overflow, radiator leaks ???

Proper surge tank coolant level is half full, cold. NEVER check or adjust coolant level with the engine warm or hot. Observe the FULL COLD legend and flat arrow molded into the top and side of the surge tank - that arrow goes over and down the tank side to about the seam.

The upper hose is supposed to get hard and hot - as coolant warms up it expands, creating the system pressure that hardens hoses, raises the boiling point, and assures "solid" coolant to the water pump.

As posted, fans don't even run in SLOW (without some A/C compressor function set) until 224 degrees. Our thermostat is set to begin opening at 188 and fully open at 206. The engine - gauge at 12 o'clock (center) - is at 190 - 205 degrees. Perfectly normal. Nicely warm.

Please study the several sticky threads on fans, cooling, and gauges on the main forum page for Engines, Northstar. Also, you might want to study the entire Cadillac Technical Archive way up ^^^ in the top black bar. Written by one of the Northstar Systems GM engineers.

During your study of the cooling system sticky, get familiar with the purge line and its cleaning.
 
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