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Coolant level rises when unscrewing reservoir cap

  #1  
Old 06-21-2018, 03:39 PM
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Default Coolant level rises when unscrewing reservoir cap

I have a strange problem that I cannot diagnose.


I have a 2006 Volvo XC90 that I just bought and I get a low coolant warning light that comes on after driving an hour or so. The temp gauge doesn't indicate overheating and the car runs awesome. I will then pull over and open the hood and sure enough the coolant is low. Here's the strange part, when I turn the cap slightly, coolant rushes into the reservoir, fills back up and the warning light goes off. I have to do this every 20 or 30 miles.


Also, when the car is completely cold and has not been driven for a day or so, when I unscrew the cap on the reservoir, air rushes in and the coolant begins to rise?



Any suggestions??
 
  #2  
Old 06-21-2018, 07:53 PM
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Normal when the engine is hot. When hot, the coolant level should be at the max level.
 
  #3  
Old 06-22-2018, 06:28 AM
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Default Not normal

This is not normal but thank you for your response...
 
  #4  
Old 06-22-2018, 06:31 AM
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When the engine is hot, it is normal. I've never seen it when cold though.
 
  #5  
Old 06-23-2018, 10:28 AM
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The coolant level will rise when the engine is hot because you are releasing the pressure that is pushing it down in the bottle. Whatever air is in the system becomes pressurized when everything heats up.

It is normal.
 
  #6  
Old 06-23-2018, 04:33 PM
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I'd have the cooling system pressure tested. You may have a bad head gasket...
 
  #7  
Old 07-16-2018, 12:08 PM
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My friend.....this is a weird problem. Possibly you have trapped air that needs to be burped out of the engine or heater core.

Basically, under pressure, trapped air in the block will compress and shrink and the water level will drop to fill the gap. When you relieve the pressure by opening the reservoir lid, the air expands and pushes the water back up to the tank. The air is collected up in the top of the engine and can't escape. As they said above, you might have a blown head gasket leaking compression gasses into the water jacket.

It is also remotely possible that you have a radiator hose expanding and about to blow. It would look like a balloon until you relieve the pressure.
 
  #8  
Old 07-17-2018, 07:07 AM
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Default Diagnose

Thanks for the post eflexer. What would you do first to try and diagnose?
 
  #9  
Old 07-17-2018, 12:35 PM
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The bulging radiator hose would be pretty obvious, probably the lower one. As you slowly open the reservoir lid, watch to see if the radiator hose shrinks. It would be pretty obvious.

Blown head gaskets can be difficult to diagnose, until they get really bad. At first they might only leak compression gas into the water jacket, pressing air into the radiator or block requiring burping. Eventually they will begin to allow water into the cylinder. When you start your car cold, there will be a white steam cloud out the tail pipe, and you will notice a loss of coolant requiring you to fill the reservoir every week or so. Finally you will get water into the oil, and your oil will have a creamy tan layer on the dipstick as oil and water mixes. So the signs are:

1. Needing to burp the cooling system (you may already have this).
2. Needing to add water to the reservoir more than once a month.
3. A steamy white cloud when you first start the car cold.
4. Creamy tan goo on the dipstick.

Have you seen anything like this?
 
  #10  
Old 07-17-2018, 12:45 PM
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I'm curious which engine you have in your 2006 XC90.

Is it the 2.5 Turbo or the V8? Each have their own characteristics and I'd like to know.
 
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