When I stop , i noted hissing sound from the coolant Reservoir. It took 3 minutes to stop the hissing. What is the problem?

 

Radiators must always vent excessive pressure, otherwise they will explode. It could simply be that. But it could also simply be leaking. If after three minutes you take off the cap to the reservoir and there is no pressure left inside, then you have a leak. Maybe a bad O-ring in the cap or even a crack in the tank somewhere. That needs to be fixed or your car may overheat. Pressure keeps the water from boiling. No pressure, and the water will boil, filling your engine with air (water vapor) and your car will not cool properly.

 

I went to a mechanic THIS PM and he conducted a pressure test. He did not find any leaks since the pressure did not dropped. I went to Volvo dealer and they told me that they made a diagnostic and they found nothing wrong. I am really confused what is happening to my Volvo Xc 90. I'm afraid that it will create more problem.

 

Sometimes snakes get into the cooling system. The large flow of hot water makes them angry and they hiss. This is probably what is going on.

 

you are weird

 

Or maybe it's the SERPENTINE BELTS!!! He he he!

 

Yes, they tend to hiss too. The serpentine belt is made of snake skin and it can hiss when the spirit moves it.

 

These cars use a closed coolant system - the coolant overflow tank pressurizes along with the radiator/hoses and gives the coolant a place to go when it expands. The port into the overflow tank is not very large - on the order of 1/16 of an inch so if the pressure test is ok, you are probably hearing the coolant just squeezing through that port as the coolant cools down and gets sucked back into the engine.

 

mt6127, Thanks for your comments. And to Tony19`63 and eflexter, I hope you will meet your serpentine in hell.

 

I'm going to have nightmares now about serpentine belts. Seriously, there is also the air conditioner system right next to the collection tank, which makes hiss noises of its own. It's really hard to tell what is making a specific unless you buy a mechanics stethoscope (yes that's a real thing). You did the right thing to have the mechanic check it for you. Sounds like there is nothing to worry about.

 

I still think that its snakes in the cooling system.

 

Altura, is this a one off incident or does it happen with frequency? Have you tried to pinpoint the source yourself, open the hood, see where it's coming from?
Even though the "experts" cleared the chance of a leak, it doesn't mean a thing! Lots of idiots in the automotive field these days don't know squat.

 

Today I had the same problem, I checked the water tank and it has a crack. As far as I know these problems happen after overheating. I read how to change this tank but does anyone knows about the causes of overheating?

 

there are multiple reasons your car may be overheating. 1) contamination in the coolant or debris clogging the radiator 2) fan or airflow issues 3) temp sensor or thermostat issues (a bad temp sensor may keep the fan from coming on or give a false positive on overheating) 4) head gasket issues 5) low coolant level

a few thoughts - when you replace the coolant tank, also replace the upper hoses, the reservoir pressure cap, the thermostat and consider testing/replacing the ECT sensor (easy to do with the top hose and thermostat cap off) Secondly if you suspect you are overheating after fixing the reservoir, make sure the fan is coming on at idle. If not, kick on the AC to see if the fan come on then. Finally, feel the upper hose - if it gets rock hard with the engine running you may have a head gasket issue and high system pressure which will require further investigation. If all is good, last thing will be to do a drain, fresh water flush and refill with new 50/50 coolant. Not sure what year you have but if its a 200X model you likely have the "blue" coolant (check to confirm what is specific to your model before refilling)

 

thank you very much for the information

the liquid is pink, i bought already coolant to replace it

y already ordered the tank it will arrive this afternoon
i Removed the broken tank and checked the Hoses and they look fine (the car has only 51,000 km)

If the temperature gauge is fine it shouldnt be overheating right? And The thermostat and the temperature gauge are different Devices

thank you very much

 

yes the thermostat and ECT sensor are separate devices - its just that to access the ECT sensor you need to remove the thermstat housing cover so its easy to do both at the same time. Not sure about the pink coolant - I've only seen that in Toyota's like my wife's Highlander (my son's Gen 1 S40 has the blue coolant) - probably not a problem but if you do decide to do a flush, buy what's correct for your car.

 

Hi everyone, thank you for your previous advice.
I changed que water reservoir and the coolant, and the temperature is correct.
I had an issue when changing the tank because the coolant got into the belts and started squeaking. At first I thought it would disappear after drying up but it hasn´t. When the engine is cold its quiet, but as soon it gets to the 90ş it starts squeaking. My engine is only 50k km, the belts look perfect. I read that it is too soon to change them or the tensors. I read about a belt spray but I would appreciate any advice you can give me.

Thank you very much