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Discussion Starter · #1 ·
My '04 XC90 T6 2.9L is having a weird issue. As it starts to heat, the coolant tanks boils. When I stop the vehicle, coolant starts leaking from the front passenger side area. I have read some posts about the cap being bad, but I don't know if that's it. It's not overheating, but I need to add coolant that's been lost to the tank. I'm pretty sure it's not a blown head gasket as that would cause it to completely overheat. Any thoughts on this?
 

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Could be a few things. The coolant is boiling because there’s is not enough circulation creating hot pockets. Could be air getting into the system, bad thermostat valve or water pump on its way out.
 

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Discussion Starter · #3 ·
I've been told it could be the cap. I don't think it's the other things because it doesn't overheat. At least with other brands, a bad thermostat would cause the vehicle to overheat. I may be wrong though. Of all the Volvo's I've had, never had this issue.
 

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Not sure on the T6 but on the 3.2 the tstat can fail not reporting an overheat.
 

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2008 XC90 3.2
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What is the history of your XC90?

How many miles?
Any cooling system work?
Any turbo issues?
How is the oil and its level? If you smell the oil in on the dipstick, does it smell like oil or a little sweet? Did the oil level creep up higher as you drive more?
Etc. Etc.

I won't say all, but electronic thermostats are designed to fail in the open position so you don't overheat. If they stick, well, then it can be in either open/closed/partial position.
 

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Leak by passenger side is normal as there is overflow hose from top of cooling liquid reservoir...

When I changed PCV I placed wrong thermostat and had the same problem.
Than I purchased complete thermostat and changed all including new gasket. Open thermostat
and if never cleaned cooling system must be very dirty inside...see my photos.
Flushing system with pressure with demi RO water will help a lot.

This is colling liquid before PCV was changed. Dirty never flushed system many years.
Now its so clean that you cant believe.

Thermostat I placed wrong inside and I replaced with new one. Check also rubber around if worn put away all.

This is for 2.5t engine not original but works perfect.



Here you can spot after flushing all system how clean is now liquid and system. See drop of liquid near tap hole...or paper soaked in.
 

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If car is very old you can use tap water hose from garden, remove hose on low level of cooler and from top
where is reservoir and thermostat push in hose and flush all system and see how many rust dirt is accumulated
in old xc90 cooling system. After you finish flush now repeat with Demi water and dont worry if some tap water remain
will not build any huge calcium deposits as people think...few drops of tap water will not kill the beast. :)
Flush it good from all possible IN OUT hoses that you can remove. Even heating core must be dirty inside from deposits.
See my old cooling liquid how dirty was inside. If you can remove thermostat while flushing will do all way around.

Several times, drain out old coolant, fill with tap water from the hose, drove around until hot, drain, fill with tap water
from the hose, drain, and repeat that cycle about 3 times. Just do it. :)
 

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OP, I'm with you on the cap--the dealer will always replace the cap when they change the coolant, so I'm guessing there's a reason for that...
 

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Discussion Starter · #10 ·
So as of now, I have changed the cap out and I just had a cooling system flush today. So far so good, only time will tell if it's fixed. Thanks for the answers thus far. I may still need to ask about this, but I need to test it for a few days and see what it does. Keep ya posted!
 

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Here you can spot after flushing all system how clean is now liquid and system. See drop of liquid near tap hole...or paper soaked in.
Hong Kong I got to ask, what is that wrapper around your hose line? And makes me wonder, do you have better wire shields to volvo brittle plastic? Mine's all cracking and thinking about better material.
 

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When I changed all PCV system and hoses I removed all possible hoses and placed in protective cable
rugged hose like you see. Like this is protected from direct heat of engine. A little and for my opinion
much better look. :) Use silicon hoses wherever you can. buy few meter and nice chrome clamps.
Its simple job and of course my car after 12 years had crack all around. There is some hoses on back side of cooling water
to be changed next job. Small short one but its time. ;)

Regarding wire you need to use high temperature sleeve white one. Soon I will change ignition cables
and will post separate thread about and photos.
 
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