2002 V70 XC coolant and misfire issues

[cbyrd87]

Hi all, first time poster here.

I own a 2002 V70 XC with 143K miles.  No major maintenance issues prior to this. 

COOLANT ISSUE

I'm getting a "Coolant Low, Stop Safely" warning basically every day right now.  I haven't found any leaks, nor has my Volvo shop, and the car hasn't run hot.  The shop said I had a crack in my coolant tank cap, which was probably letting coolant boil out of the tank, hence no visible leaks.  But replacing the cap hasn't helped.  Every time I check the levels when the car is cold, the coolant is down to the minimum level line.  I opened the tank this morning to add coolant.  There was a hiss when I took off the cap, and some coolant flooded back into the tank.  Has anyone seen or had this type of issue? 

MISFIRE ISSUE

I've done some more work on this one, but no luck so far.  My car runs rough at idle for 30 to 60 seconds, usually after it's been sitting a while.  This usually only occurs right after I start it, but if I leave it in park for a while it will start to run rough again.  Once it evens out it doesn't do it while I'm driving.  The check engine light is also on.  My shop replaced my spark plugs, which were getting old. They also got a code for a misfire on cylinder 5, so they replaced the coil there.  None of that has helped. In fact, the issue has become more frequent.  Any ideas on some other possible sources?

[Ihatespeedbumps]

The two are possibly related. Do you see any smoke in the mornings on cold start up? Have you witnessed the engine overheating at some point?

[cbyrd87]

I haven't seen any smoke, nor has the engine ever overheated.  It's been sitting at the shop for a week and they haven't been able to figure it out.  They said the only possible explanation is a possible minor break in the head gasket, and they recommended that I take it to the dealership to get it looked at.