V70 "disappearing water"

2000 V70 2.5l fwd turbo

found i had a small leak in the reservoir for coolant- it was coming from a
hairline crack in the bottom of the tank near the hose connect.
replaced it with a new volvo unit and a new coolant level sensor (the old
one quit working)
now i am still losing about a pint or so of coolant a week. sometimes the
reservoir will be below the minimum line, and
sometimes when i release the pressure from it, it will fill back up to near
maximum. it's almost like i have air bubbles in the cooling system
somewhere.
i know people are thinking head gasket, but there is no oil in the water, no
water in the oil - so if it is a head gasket then the exhaust gases are
getting into
the water jacket somehow, but also causing no symptoms whatsoever. car runs
starts fine, has good power, has normal exhaust- not white, not excess
water vapor...
my question- is there a hose/spot where water could leak slowly and be
vaporized by engine heat and not be noticeable upon inspection??
i have not found any further signs of leakage...

 

did ya check around the water pump assy?

 

Yes.

If the head gasket leaks, but only toward the outer part of the
engine, and there is now break in the gasket between the water and oil
passages, you will lose coolant without finding contamination in the
oil or water.

Look for a white line going downward from the head: on mine, it was
toward the front, on the driver's side.

 

Handy trick for this is get an old coolant tank cap, drill a hole and
install a tire valve stem, and then use a hand pump to pressurize the
cooling system to 1-2 psi with the engine cold and look for leaks. Small
leaks will usually only leak steam when the engine is hot, but when you
pressurize it cold, they drip liquid. Don't get carried away with the
pressure or you will create a leak where there wasn't one.

 

On a different make of car I had a head gasket go with a pin-hole leak
between a cylinder and a water passage, it was using about a pint every
couple of days or 100 miles, the only symptoms were water loss and the
water taking on a dirty grey colour with a smell of exhaust gasses.

A garage will be able to tell you if the head gasket has gone by doing a
pH test on the coolant. Exhaust gasses will turn it acidic (I believe.)

A pint of water a week is a trivial amount for an engine to burn
through, it will make no difference to the running. An engine will
produce far more H2O from the normal combustion process.

 

I like c30!
guagua
"~^ beancounter ~^" <>
??????:...
did ya check around the water pump assy?

 

Check very carefully around the coolant inlet connection (the top one)
on the radiator. The plastic connector on Volvo radiator tanks is
known to crack and gradually leak coolant at that spot. You may only
see a thin impossible-to-see white line of sediment at the base.

It happened on my V70 at about 100k miles.