What leads me to believe there is a head gasket issue:
– The cooling system seems to over-pressurize. When fully up to temp the upper radiator hose seems to be almost rock hard.
– I have noticed within the last 6 months that it goes through coolant. Not a ton, I probably fill it from the low mark to the full mark once every 2-3 months. I don’t see any external leaks – no clear sign of leaking coolant from the radiator, no obvious sign of it coming from the water pump, heater hoses, or heater core either.
– I actually bought the car after the heater core blew (filled the cabin with steam, not just a failure where it trickles out like I have commonly seen associated with failed heater cores) on the previous owner while he was driving. He said he towed it to the shop, but drove it home 1.5 miles from the shop with just about no coolant in it (I worry this could have caused an overheat situation leading to head gasket woes). From the paperwork the PO provided it seems like they replaced the radiator within the year of me buying it as well.
– I have owned this XC70 for about a year and a half now, and driven it around 15,000 miles. In this time I have seen the temp gauge go up twice: once while idling in the warm humid summer night for about 30 minutes, and once while testing the AWD in an empty, snowy lot. Neither time did it reach the red and I turned the engine off as soon as it started creeping up above the normal mark. Both times were low airflow situations so I have since replacing the radiator fan in the case that that is what was causing it issues. I have not experienced the temp creeping up since but I also am careful to not let it idle for long periods now.
– I pulled the spark plugs today and noticed a dusty green material on the ground strap of some cylinders. I am not well versed in reading plugs, but heard once that burning coolant can cause something similar.
I have run a sniffer test on the overflow tank and it passes every time (so it is not detecting exhaust gasses in the coolant system).
Attached are photos of the spark plugs, with the cylinder number in the top right corner.
So, what does everyone think? This Volvo has a fair bit of issues at this point, so I am weighting when and if I should go ahead and fit the head gasket if it is bad (the car is oil soaking the t-belt too I was going to go ahead and replace that, but if the HG is bad and I decide to replace it I will most likely wait till I pull the head to just replace the belt at the same time).
