My 07 Sienna sat for two weeks while I drove my Mother's Santa Fe 2.0T, in that time I started it twice and did not notice any issues. I returned her Santa Fe on 08/13 to resume driving my Sienna Friday morning. It started right up and I left my house, it was 53 degrees outside. I drove about .4 of a mile to the gas station and filled the tank. From there I drove in town for about 2 miles and then up to highway speeds.
After about 15 miles I noticed the engine was not warming up to it's normal temperature the gauge was only about 1/4 of the way up. The heat was not blowing very warm at all, I arrived at a grocery store about 5 minutes later. It was 5:25 AM so I had a few minutes to wait for the store to open. As I was sitting there a elderly man in a 1st Gen Sienna got out of his car and approached mine. He informed me that he had his window cracked and got a strong whiff of anti freeze from my van. I then exited the vehicle and immediately noticed it was definitely my van. It was coming from the grill and wheel well. I immediately drove it back home and got a ride to get the Santa Fe back. The van sat the rest of the day Friday. I did take it out yesterday to see if it would do it again. I drove it for over in hour in 90 degree temperatures with the A/C on full blast. I even sat in traffic for 20 minutes and the temp gauge stayed perfect. I went out about an hour ago (1:30 AM) with the temperature of 58 degrees and tried the heat again. It would not warm up fully but the smell has not returned. The next door neighbor tried telling me it is a leaking head gasket but wouldn't it have overheated on the drive?