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Hey all, I have fixed so many things on my 2007 SB9T with help from this forum, so wanted to start off with a thank you! This latest problem is a new one, and I can't find anything similar posted in the forum. If I cant identify whats wrong, I think it could possibly be the end of the run for my Tribeca.

Background:
235k Miles - 35k miles ago, car overheated and we had a partial rebuild completed. New heads and new HG installed by the dealer. The car would occasionally run warm 1-2 above in summer 100F outside with AC on, but the dealer said this was acceptable after the repair and would level off. It did, and made it through 2 summers, by the 2nd summer it would very rarely go 1 above even in the hottest of summer with the ac on full blast. Then this past winter, I noticed a small coolant leak and a low level in the overflow tank. While driving up a hill, my beca got 2 ticks above normal temp and I pulled over. I checked the expansion tank, and it was completely empty and bone dry. I topped off the tank and this was the start of my running hot issues.

The attempted fixes:
I assumed that it sucked in air, which then for the next few weeks while driving carefully it would occasionally get 1-2 above and overflow the tank would be overfilled. I would siphon out the expansion tank and refill the radiator. There was no loss of coolant, so I just assumed that I had airlock in the system because the passenger side stopped blowing heat(remember this because its either a symptom, a clue, or a red herring) until I refilled the radiator. Then would run fine for a day or so until the expansion tank overfilled again, rinse and repeat. I noticed that the car would run at normal temps, but as soon as the passenger side stopped blowing heat then shortly after the car would start to run hot.

There was clearly an issue in my cooling system, so I did the cheap fixes:
  • Replaced the OEM thermostat with a new OEM thermostat. Tested both, the one I replaced was faulty and opened 10 degrees too late and would not open fully(which leads me to believe this was the cause of the intermittent running hot in the first place).
  • Replaced the non OEM rad cap, with OEM rad cap
  • Replaced the coolant with new OEM coolant
After these fixes, the system got better but would still run hot occasionally while driving and would overflow the expansion tank, except NOW there were bubbles in the expansion tank and microfoam. I assumed at this point that it was HG failure again, but was hopeful because the car never overheated and would go 2 above at most. Then I noticed that the radiator was warped at the bottom and there was a crack in the radiator frame, which lead to an expanded core line in between the fins. There was no visible leaking of coolant so I deduced that it was possible that air was getting into the system from negative pressure and then causing the coolant to boil, which could explain the bubbles and the foam. SO, next round of repairs:
  • Replaced the radiator with a new OEM radiator
  • Replaced the coolant again
  • Followed proper burping procedure
This is where it gets interesting. After these repairs, the car started to act all wonky and is now undrivable because when in gear it gets heat spikes 1-3 ticks above normal operating temps. While it heats up fast, it comes back down to normal temps really fast too after I pull over and let idle.

I have tested and noticed the following:
  • I was able to get all of the air out of the system following the proper burping procedure.
  • During idle, the heat works great on both sides and I have run at idle for over an hour without any issues.
  • I have tested and ran prolonged high rpm at 3-4k rpms and the car will get up to temperature and behave normal. The fans kick on and off and everything works as expected.
  • When I drive the car, I get maybe 20 minutes of driving and the passenger side heat will cut out and car will start to run hot and the coolant will start to fill up the expansion tank.
  • I have not noticed any bubbles or microfoam in the expansion tank.
  • The coolant is not being burned, and there is no oil in the coolant nor is there coolant in the oil.
  • There is negative pressure build up, and the radiator pulls the coolant back into equilibrium and radiator does not need to be topped off anymore.
  • Fluids are OK, there is a small oil leak around the rear engine temp sensor and oil pressure switch
  • Transmission fluid is overfilled somehow, but I checked it cold...its a little dirty reddish brown but still smells sweet
  • The only code thrown is for the catalytic converter passenger side which needs to be replaced
  • The passenger side front brake caliper occasionally gets stuck, drags on the brake. This is because brake pads and rotors need to be replaced.
I am fresh out of ideas. Any thoughts? I would hate to junk the car but I can't figure it out and its super frustrating!

*mods I reposted this because I think I made too many edits on the first one and it has been stuck waiting for approval
 

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You may have a soft hose that is collapsing and thus restricting coolant flow, but then you would think it would do it at the prolonged high rpm's you are talking about. What about a water pump?
On the sticking brake, you probably just need to remove the caliper and clean and relube the slider pin.
 

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Discussion Starter #3
I thought maybe water pump too, but wouldn’t it be leaking? The hoses are all new and were replaced at the same time as the hg repair
 

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Ouch, this is a tough one. You've replaced the radiator (I was concerned about leaking in to the transmission, but the new radiator would have solved this).

I really sounds like headgasket leading to gas in the coolant system causing spikes in temperature.

Tom
 

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Discussion Starter #5
Sadly Tom, I think you are right. It is likely in the early stages of a HG failure. It seems that after it is left to cool completely, and if the radiator is full, it runs fine for a while. After rigorous testing, it appears that sustained driving around 2000+ rpms that starts the chain reaction...gases get in the system, coolant is pushed into the expansion tank, loss of heat from the passenger side, and the car then runs hot because of the low coolant. I do not have another 2-3k that I want to invest in this car, so it seems today is the day it gets sent to the U-Pull-It to offer its parts to the remaining Beca's on the road. Its a bummer too since I the new radiator has maybe 10 miles on it :(
 

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Sad... I'm sorry... Unfortunately all dealers and there techs are not created equal. Sometimes they don't prep the block correctly to get it flat enough.
 
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