I have 2001 Subaru Outback 2.4L Automatic wagon with about 190K miles. It runs great, however when it gets below 40 degrees farenheit, it has a few symptoms that are not present when the weather is warm.
1. Strong odor of gasoline, so much so that I cannot turn on heat unless the car is moving and wind is forcing the order to leave the engine area.
2. Overheating when driving more than 5-10 miles, regardless of uphill or downhill.
At the end of last winter, I replaced the thermostat, drained old coolant, then refilled the system with 50/50 coolant to make sure I had a proper mix. Sure enough, I drove about 10 miles, and immediately saw the engine begin to near the red line. After this, I brought it to a mechanic and asked them to look for any problems and possibly check the water pump. They gave it back to me and told me the water pump wouldn't fail the way it is engineered, and they claimed that it had to be a head gasket problem. I don't believe they actually checked anything out because they didn't charge me after leaving it with them for three days.
So, I saved up a little cash and it was around May, when things started to warm up. When I was ready to bring it in to have the head gasket replaced, the weather had consistently risen to 50-70 degreees farenheit and I was no longer having overheating issues. I was testing it on hills, and with AC on full, trying to get it to overheat with no success. So, I figured even if they replaced the head gasket, I couldn't verify that their work was successful until it got cold again, so I didn't do it. Now that we've had a couple weeks where mornings are below 30 degrees, all the symptoms are back, and they seem to be worse when it is really cold than just cold.
I don't have anyway of proving that the gas odor and the overheating are related, but I never have one without the other. If I lived in a warmer climate, I don't think I would even be aware that there is an issue because it drives great in the summer and I have no issues, even on long road trips with the car packed and AC on full blast.
Other info... I didn't see any excessive rust or metal particles when I flushed the coolant, I've always changed the oil regularly and i've used synthetic oil since it cleared 100K, no major mechanical failures but have replaced starter, alternator, knock sensor, belts when worn. Timing belt changed at 125K. Flushed & changed transmission fluid at 150K. I've regularly replaced spark plugs, spark plug wires, & distributor cap, but I've never replaced the fuel filter or anything fuel related because I was always afraid of a spill and stinking up the garage and having to hear my wife complain for weeks while the smell went away. Please help me!! I've aked every mechanic that I've randomly run into and they only tell me that it's either thermostat, water pump, or head gasket, however none of those suggest that it would work fine in the summer but overheat and stink in the winter. Any insight and explanation could help. I'm at a loss. I don't want to spend $1500 for a head gasket replacement and find out that it was some other anomoly that only costs me $50. I love my Subbie and hope to get her to at least 300K miles.