Hi Allen,

What year is your V70. I'm hoping I'm on to something here.

My heater core was doing the same thing as yours this
fall so I started doing much research as I do not believe
these cores should blo in 3 or 4 years. To make a long
story short I found that my existing coolant[ 45 months ]
looks like vinegar.

Have you ever had your coolant changed?

Volvo says you should never have to change your OEM coolant
but I think many cars are going to suffer in the near future.
Thermal protection is probably fine but I think anti corrosion
propertise dissipate.

I am slowly swapping my new coolant thru the reservoir and my heater
core is responding nicely. Will get a full flush in the spring.
Keeping my fingers crossed.

Check your coolant by using a turkey baster and putting it
in a clear empty spring water bottle. See if color is golden
like honey and clear. If that is the case then the OEM extended
life coolant's anti corrosion properties may be breaking down.

I read new coolant has some sealant properties in it.

Please let us know.

rd