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06 Rendezvous overheating & no one can tell me why!

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Sep 7, 2017, 2:35 PM

Post #1 of 3 (842 views)
06 Rendezvous overheating & no one can tell me why! Sign In

2006 Buick Rendezvous, 3.5 l engine.

My wife's car overheated one fine day in our August Arizona heat only this is not your every day ordinary typical overheat problem. If you'd like to be challenged please read on. For this past summer, the AC worked but it was never ice cold like it had been previously. No problem, we toughed it out. Engine light is not on. I've never done any maintenance on this car's cooling system since owning it. I did all the normal stuff so far...

* Replaced radiator cap
* Replaced thermostat to a 185 degree
* Flushed radiator (drain...fill with radiator flush for a while...drain...flush with hose...refill with Dex antifreeze 50/50 with distilled bleeders to remove air some more...bleed more air...etc)
* Checked for leaks...none found

One unusual thing I did find is that when I opened the upper bleeder screw, green colored fluid came out (Dex is orange). When I opened the lower bleeder, clear fluid came out. I thought maybe I hadn't properly flushed the engine and maybe the last guy put regular antifreeze in instead of Dex. I can't figure out the lower one bleeding clear fluid though.

Now the car engine is running cool like it should. 2 weeks go by and all is fine...when all of a sudden...BAM! The temperature gauge needle buries itself to the far right in overheating mode! Alarms are going off that it's overheating so I shut it down. I wait for it to cool and drive it home. I tried bleeding it some more. Start it and all is fine again. The car then runs at normal temp for another week or so but again...with no warning...BAM! Overheat alarms! Nothing else has changed. I'm still driving it in the middle of the day when it's 108 outside and it is usually okay with that. But how can this car possibly run fine for a couple weeks in severe heat and then only suddenly it decides to overheat. Once it's cooled down, it will run okay for a while. Help?

Ultimate Carjunky / Moderator
Discretesignals profile image

Sep 7, 2017, 6:16 PM

Post #2 of 3 (825 views)
Re: 06 Rendezvous overheating & no one can tell me why! Sign In

When it was running hot, was the air blowing from the cooling fans hot? Were both heater hoses hot? Were radiator hoses hot? If you turned the heater on was the air hot? If you have a temp gun, what was the temp at the coolant sensor body? Any trouble codes stored? Any loss of coolant? Was it overheating at highway speed, sitting at a light, or both?

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 7, 2017, 6:19 PM)

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 8, 2017, 1:47 AM

Post #3 of 3 (795 views)
Re: 06 Rendezvous overheating & no one can tell me why! Sign In

Quote">* Replaced thermostat to a 185 degree<"
Just that: Put right thermostat in this or it's never going to run properly or know what it's doing by temp controlled by computer it's messed up with just that. I know it can be hot outside but engine doesn't want to be that cold or may cause that overheat alone + other things not knowing what to do yet with wrong parts in it,

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