XC70 bubbling expansion tank

srw8553 · May 28th, 2014, 07:55

I'm currently touring in Austria towing a caravan and have noticed when I stop after a couple of hours for a break there is a bubbling sound from the engine cooling system water expansion tank. All levels are normal and the water temperature gauge also shows normal. There is no sign of fuel or oil contamination in the water and no sign of water in the engine oil. The bubbling sound stops after a few minutes. I have stopped after an hour and there hasn't been any bubbling. Also after hearing the bubbling after two hours driving I've stopped again within 30 mins and there's not been any bubbling. I've been towing with this car for about six years and this is the first time I've noticed this. I called at a garage in Germany and they couldn't find a problem or give an explanation. Any suggestions very much appreciated.

oragex · May 28th, 2014, 09:40

How many miles on the car? The expansion tanks are known to fail, either cracks in the plastic (without loosing coolant) or the cap lets air inside and the tank looses pressure.

Georgeandkira · May 28th, 2014, 12:27

Hello, The absence of coolant/oil contamination is good news indeed.

I know that a failed cap will result in a loss of pressure which will let the coolant bubble. For the number of times I've read posts on the subject, I'd take the financial risk of buying a new cap as a diagnostic.

If you're not too squeamish you can remove the cap one morning-when the engine is cold and no one is looking-make a shield from plastic wrap and blow gently into the reservoir. You might get lucky and actually hear the leak. It could be near the top of the reservoir just beneath the cap's threads.

If the condition continued I'd look into a system pressurizer. Again, I think these testers-a pump with a pressure gauge which screws onto the reservoir's top in place of the cap-are cheap enough to buy.

I also think the big concern there, in addition to knowing what you're doing, would be to make certain the pump/tester you buy fits or has an adapter to fit our coolant reservoirs. Kira

srw8553 · May 29th, 2014, 07:48

Thanks for the replies. The car's done 226,000 miles. I'll look at the cap and the tank.

Thanks again

jgjones095 · May 29th, 2014, 15:02

I posted a few weeks back probably a month or 2 now a similar issue with my v70xc

I oosted a photo mine has tiny cracks only visible cos of a different white colour

Still to repair mine though

May 28th, 2014, 07:55	#1
srw8553 New Member Last Online: Dec 16th, 2015 15:33 Join Date: Jul 2011 Location: Ashby de la Zouch	XC70 bubbling expansion tank I'm currently touring in Austria towing a caravan and have noticed when I stop after a couple of hours for a break there is a bubbling sound from the engine cooling system water expansion tank. All levels are normal and the water temperature gauge also shows normal. There is no sign of fuel or oil contamination in the water and no sign of water in the engine oil. The bubbling sound stops after a few minutes. I have stopped after an hour and there hasn't been any bubbling. Also after hearing the bubbling after two hours driving I've stopped again within 30 mins and there's not been any bubbling. I've been towing with this car for about six years and this is the first time I've noticed this. I called at a garage in Germany and they couldn't find a problem or give an explanation. Any suggestions very much appreciated.

May 29th, 2014, 15:02	#5
jgjones095 Master Member Last Online: Feb 28th, 2024 22:04 Join Date: Feb 2013 Location: South wales	I posted a few weeks back probably a month or 2 now a similar issue with my v70xc I oosted a photo mine has tiny cracks only visible cos of a different white colour Still to repair mine though __________________ Who said Volvos were build to last? 2.4t V70XC Auto 2001 165k D5 185 XC70 M66 2006 202k

May 28th, 2014, 09:40	#2
oragex Premier Member Last Online: Jul 26th, 2021 21:24 Join Date: Jun 2013 Location: Coldnada	How many miles on the car? The expansion tanks are known to fail, either cracks in the plastic (without loosing coolant) or the cap lets air inside and the tank looses pressure.

May 28th, 2014, 12:27	#3
Georgeandkira Premier Member Last Online: Yesterday 14:34 Join Date: Feb 2009 Location: Hackensack	Hello, The absence of coolant/oil contamination is good news indeed. I know that a failed cap will result in a loss of pressure which will let the coolant bubble. For the number of times I've read posts on the subject, I'd take the financial risk of buying a new cap as a diagnostic. If you're not too squeamish you can remove the cap one morning-when the engine is cold and no one is looking-make a shield from plastic wrap and blow gently into the reservoir. You might get lucky and actually hear the leak. It could be near the top of the reservoir just beneath the cap's threads. If the condition continued I'd look into a system pressurizer. Again, I think these testers-a pump with a pressure gauge which screws onto the reservoir's top in place of the cap-are cheap enough to buy. I also think the big concern there, in addition to knowing what you're doing, would be to make certain the pump/tester you buy fits or has an adapter to fit our coolant reservoirs. Kira

May 29th, 2014, 07:48	#4
srw8553 New Member Last Online: Dec 16th, 2015 15:33 Join Date: Jul 2011 Location: Ashby de la Zouch	Thanks for the replies. The car's done 226,000 miles. I'll look at the cap and the tank. Thanks again

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