I have a 98 deville losing coolent and running hot now here the problem it dont run hot until after i get to work or right before. about 30 min driven, it don't lose water until after i turn the ac on and after 10 to 15 min of driven all coolant is gone and it running hot no sign of water leaking from anywhere i even change the oil twice to see if i had water in there oil is fine no sign of white smoke from tail pipe or any other sign of head gasket problem i replace the radiator and about to change the water pump, new thermostat have no idea what else can be the problem it seam to me the temp outside have some input to it also if this help it just start warming up and it overheating more faster now before in cooler condition i ca drive for and hour before it run hot, silly huh

 

Have you had pressure done? If not you need to. Heater pipes that run accross rear head tend to rot out, at the clamps that hold them, causing sometimes a hard to find leak. Crossover gaskets also tend to seap/leak. Have a CO test done to verify head gasket is not blown. If nothing shows up replace thermostat. Also Check water pump belt, tensioner, and pulley on camshaft.

 

No have not had a pressure test done yet, next on the list don't think it the water pump the belt look new and no sign of leak from there im starting to think it a problem with my fans tonight was cool on my way home from work it never reach 200 off or on the highway when i left from work at 600 pm it went from 217 to 245 and drop when i exit off to 225 made a left drop to 217 drove straight for about 30 sec went back up to 233 and 254 stop and check for any leaks nothing car still running look at the temp say 207 never cut it off it alway cool off in park I had this car since Oct 2009 replace radiator from past leak i found about two month ago been having this problem, since i change it.

 

Is lower deflector in place.... mounts to front bumper and core support? (they tear and sometimes fall off,causing overheating at higher speeds) Sticking thermostat cause irratic temp readings and sometimes coolant lost ; bubbling out surge tank. Is surge tank full? (about 1-2 inches down)

 

when it run hot there is a lot of noise coming from spill tank and water come spitting out the overfill hose on top of tank as far as the lower deflector i have no ideal what u talking about, Can u please tell me where the crossover gaskets located at and tank sometime take a little water as long as it dont run hot a have to say a quart of water sometime two if left for a week i might add a gallon into tank

 

I just bought a 2002 Deville with 80k miles and I'm having a similar problem (overheating at high speeds / longer drives). My mechanic is having me first try a product from 'Bars' to try and fix any potential leaks.

However, it overheated on me WITH coolant in the system on a 1 hr drive at 75 mph and then seemed to correct itself moments later.

What is the story with this deflector thing? Does it confuse the thermostat? What does it do?

I appreciate your help and comments.

 

if i can figure out why coolant come out the reserve tank and come out the overfill hose i would be good this is how i am losing coolant causing it to run hot any ideals???

 

Deflector...if you have a clear view of ground when hood is open looking between bumper and radiator - its missing. Bubbling make sure cooling fans work, thermostat is where to start if they operate. 02 Deville same thing but at highway speeds cooling fan is not necessary, still deflector needs to be there however its plastic (more durable doesn't fall off as often). New to you car? CO test a must to be sure head gaskets are intact.