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Discussion Starter #1
I didn't drive the car much this winter. Started driving it regularly last week.

Coolant was always rock solid at 195 degrees. No matter what--interstate at 85 mph, idling in stop-and-go traffic for an hour...195 degrees.

Now it'll get as low as 188 degrees on the interstate and it will overheat if I'm not moving. It'll get up to 225 degrees after I stop the engine.

The fans seem to come on. I took it to an auto electronics guy I trust and he said the fans are coming on and thought the coolant was low.

The coolant level is fine. It's not leaking any coolant (well, except when it boils over). I can't hear the fans like I think I should--I think they're intermittent, but they definitely do come on. Though the fans wouldn't explain why it gets below 195 degrees on the interstate.

I got nothing for this--it's not leaking coolant, it's just not...cooling.

It's a 2006 6.0, fwiw.

Anybody heard of this, or have any ideas on where to start?

Thanks in advance.
 

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'05 CTS-V
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Any mods? Has it ever been tuned?

The stock fan setpoints are something like 224 and 232F, so if it hasn't been tuned (which may have included changing those setpoints) then it's perfectly normal for temp to rise into the 220s if you're at a stop or moving slowly (stop-n-go traffic or whatever). I can't explain why yours would not have behaved that way in the past; that's what mine always did when it was stock. Now that mine is not stock, and the fan setpoints have been changed in the tune, it only goes over 200F if I'm on track.

"Over cooling" at speed typically means there's some sort of issue with the thermostat, that it's allowing more flow than it should.

The coolant level is fine. It's not leaking any coolant (well, except when it boils over).
Are you actually boiling over and spewing coolant out of the reservoir / recovery tank? If so, the cap on the recovery tank is dead and not maintaining system pressure. Your coolant should not be boiling over at the temperatures you're seeing.
 

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Discussion Starter #3
Any mods? Has it ever been tuned?

The stock fan setpoints are something like 224 and 232F, so if it hasn't been tuned (which may have included changing those setpoints) then it's perfectly normal for temp to rise into the 220s if you're at a stop or moving slowly (stop-n-go traffic or whatever). I can't explain why yours would not have behaved that way in the past; that's what mine always did when it was stock. Now that mine is not stock, and the fan setpoints have been changed in the tune, it only goes over 200F if I'm on track.

"Over cooling" at speed typically means there's some sort of issue with the thermostat, that it's allowing more flow than it should.


Are you actually boiling over and spewing coolant out of the reservoir / recovery tank? If so, the cap on the recovery tank is dead and not maintaining system pressure. Your coolant should not be boiling over at the temperatures you're seeing.
No mods. And it'll get hot enough that it throws an error on the DIC screen and goes into a restricted mode or something like that.

It will puke coolant out of the recovery tank when it gets that hot.
 

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When is the last time you flushed the cooling system?

You may have scale building up, and I would check the thermostat also. It may not be opening fully, and this may have occurred while it was sitting. Dex if left for a long time can build up sediment. Try a drain and flush and see if that helps.

You can also check your fan relays to ensure they are working properly and switching it on and off in high and low.

-Byron
 

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No mods. And it'll get hot enough that it throws an error on the DIC screen and goes into a restricted mode or something like that.

It will puke coolant out of the recovery tank when it gets that hot.
So how hot is it getting? Your first post mentioned 225F, which is perfectly normal. Even into the 230s isn't an issue. I've seen coolant temps in the low 230s and have never gotten any sort of warning.

I think the cap on the recovery tank is toast, based on the fact it's actually boiling over. If the cooling system isn't holding pressure, then the coolant will boil at temperatures at which it should not normally boil. Steam doesn't transfer heat as well, so the cooling gets worse.
 
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