Mysterious coolant loss, Volvo S60

2008 Volvo S60 2.5 T AWD.  Low coolant message.  Checked and added about a cup of coolant, to bring level up.  Drove it as normal, for about 10 days, message returns.   Add a little to bring level up.  Checked the obvious.  Radiator and hoses, overflow tank line needed to be tightened.  Heater lines going into firewall.  No  milk on the dip stick, no sweet smell in exhaust, or white smoke.  Check inside for the heater core, wet floors, and coolant smell.  Nothing.  

Cold and rain here, icky gravel driveway, in my open air garage.  Can't get under it right now.   Any ideas what to look for?   Waiting to do a pressure test.  Thoughts would be appreciated.  Thanks.

My experience with BMW compels me to suggest a fracture in some plastic component. BMW expansion tanks are notorious, but really any plastic bit in the system is suspect. Pressure test will likely reveal your culprit.

I'm guessing water pump.  They typically only leak when the car is running and if it's only leaking a little it can evaporate before it hits the ground.

When I bought the car, the timing belt had just been done.  I will put a call into the dealer, to see if the water pump was also done, when they were in there, doubt it though .  It was a one owner car, with some service records.   Car has 124k on it, belt done at 122k.    These cars apparently don't have much of a history with water pumps, but I'm looking into it.

In reply to 02Pilot :

I tightened up the overflow hose, saw some dried stuff around it.  A new cap and expansion tank are pretty cheap, might just replace it any way.

Water pumps on white block Volvos last forever.  Really, the only things that ever leak coolant on a volvo are the rad, the overflow tank, or the heater core orings.

Once, about 15 years ago, one had an external leak from a broken head bolt.

Thanks.  Due to the crappy weather, can't get under the car right now.  The radiator from what I can see, looks OK.  The overflow, I'm going to replace regardless, good PM.    Now, the heater core rings.  I checked the firewall side hoses, seem OK.  Do I check drivers side for the inside O rings?   That's where they appear to go.  Looks like a tight fit for a one armed fat guy.

I don’t know how similar the P2 chassis Volvos are to the P80, but I was having the same mysterious issue with my P80 ‘96 850. It turned out to be the heater core.

No coolant smell inside, no wet carpet. Only noticed the driver side floor board wet under the carpet after lifting it.

Fairly simple to replace (compared the the nightmare my BMW e23 was) and I replaced the o rings too. On mine the heater core was in fact cracked. 

In reply to Carson :

I'll check  that out.  Pretty sure it's just some panels to come off.   But, the way things happen for me, I'll have the whole interior out.

Strange, I posted in your thread last night but there is no evidence of it today. 

Anyway, next time the engine is warm, turn it off and squeeze the upper radiator hose. You may find a pinhole in a hose. 

Thanks.  I'll try that, although I did check the hoses and clamps, and nothing.  I did run the car, no drop in coolant, but it did seem to rise a bit in the expansion tank. Not sure what that means.  Did not overheat, and ran fine, idled fine.  Too damn wet to crawl around under it.  Next, is check the O rings to the heater core.  Been busy fixing my daughters car.

If it is a small crack it will only leak at high pressure and evaporate as soon as it comes out. Check for smell right after you shut off a hot engine. The best way is to pressure test it.

Pressure test to be done this week.  I'll trot out to a buddy's shop, and go  from there.  Hoping not a HG, but from what I gather, these engines aren't prone to that.  Probably something goofy.

Haven't been able to pressure test the system, due to my 95 year old Mom fell and broke her hip.  Lucky I bought stuff from FCP Euro, on here, returnable.  Squezzed some time out to replace Expansion tank, which I promptly broke the tabs off of,  and snapped the tab off the power steering tank.  Enough destruction there,  so I moved on to the radiator hoses.  I guess the Scandanavians have small hands, or elves putting hose clamps on.  Top clamps were difficult at best.  The screws were on the bottom.  By now it's dark, and tomorrow is a Noreaster.  By the way, that Volvo coolant is some slippery e36m3.

Replaced some hoses, and expansion tank.  So far,so good.  Sniff test found a very small leak? near the overflow hose to the radiator.  Looks like a PIA to get to it.  And it's right there...... under the radiator support.

Rad/condenser/intercooler drops out the bottom...

Thanks.  It's a shame you have to go through all that to check a hose connection.  That's a gripe I have with modern cars.  Simple maintenance items are made to be not so simple.