Boiling coolant

Tiny
RANDI BUSSANMAS
  • MEMBER
  • 2006 VOLVO XC90
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 220,000 MILES
In the month I have owned the car, the coolant has boiled and then drained into the parking lot two times, only while idling. The temperature gauge never goes past mid-line. It will run and hold coolant consistently for two weeks, then idle, boil, and dump it from the front passenger side directly behind the bumper.

Any ideas?
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Thursday, December 10th, 2020 AT 9:09 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

It sounds like it's coming out of the expansion tank. Does this only happen when you are at idle? Also, does the temp gauge indicate it is overheating, or does it stay in the middle when it happens? When it happens, are the cooling fans running under the hood?

I'm asking these questions because it can be caused by a few things. First, if the cooling fans are not turning on, it will likely overheat when the vehicle isn't moving. So that would be likely related to a bad fan motor or an electrical issue. If the temperature gauge is indicating a hot engine and the fans are running, then suspect a thermostat. If, however, the fans are running and the engine temperature is not past normal, it could be related to a bad head gasket.

Also, I'm going to provide a link that explains how to check for a bad head gasket. I want you to look through it. There are a few things you can identify just by opening the hood and checking things. Do this and let me know.

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know the answers to my aforementioned questions. That will better help me identify potential issues.

Take care,
Joe
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Thursday, December 10th, 2020 AT 6:49 PM
Tiny
RANDI BUSSANMAS
  • MEMBER
Hi Joe!

Thank you for taking the time to respond!
It has only happened to me while the car was idling; never while on the move. The thermostat has never moved beyond the mid-line, even when the reservoir was boiling (as in, blew the lid off boiling waiting in line for a Christmas Light show the other night).

As to your question about the fans: I honestly have no idea. I didn't think to listen for them and have always immediately turned the vehicle off after I saw the drainage.

Before taking it into the shop today, I checked the oil and it was perfectly normal- no milky goo. There has also been no cloudy/white exhaust. The techs hooked it up to whatever delightful machine tests the pressure for the cooling system and it held perfectly. They let it idle for over an hour in the bay, test drove it three different times (with and without A/C blasting) and could not get it to repeat the malfunction. They were left scratching their heads, and I was left shaking mine. I was sent on my way with instructions to return if and when it happens again.
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Thursday, December 10th, 2020 AT 10:25 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
The confusing part is that it boils over but the temperature gauge indicates it isn't overheating. That leads me to believe there could be compressed air from the cylinders into the cooling system. When you checked things, did you note if there were bubbles in the coolant? Also, have you tried replacing the lid on the expansion tank? Don't laugh, but when the system is pressurized, the coolant requires a higher temperature to boil. (Or lower to freeze)

Let me know. The idea that it happened when you were at idle, would point me in the directions of the cooling fan, but again the temp gauge doesn't indicate an overheating issue.

Let me know if you checked for the bubbles in the coolant. Also, let me know if the coolant appears clean.

Take care,
Joe
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Friday, December 11th, 2020 AT 9:11 PM
Tiny
RANDI BUSSANMAS
  • MEMBER
I have seen zero bubbles in the darn thing excepting the boiling bit! It runs clear and smooth (I watched obsessively for bubbles because it was an indicator for blown head gasket which has me spooked).
I have not tried a new lid. But the entire tank was replaced a little over a month before I bought the car. I even still have the original tank, so I may try swapping lids!

The temperature gauge might just be messing with my mind on purpose: something somewhere has to be happening. Or the coolant wouldn't empty itself into a parking lot every two weeks. Both times it was idling with the air conditioning on: could that be a major factor? Also, it was perfectly sickly sweet and clear- well, violently yellow at least, but no discoloration!
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Saturday, December 12th, 2020 AT 3:51 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

Try the different lid to see if that makes a difference. As far as the A/C and at idle, yes that can contribute to the problem simply because the A/C places a load on the engine. When you turn the A/C on, the cooling fan should turn on. See if you hear it turn on. Also, if this happens again, pay attention to the fans. If they seem to work when the engine doesn't overheat and not when it does, the coolant temperature sensor may be the issue.

Let me know.
Joe
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Saturday, December 12th, 2020 AT 10:26 PM

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