Yesterday I spent the afternoon washing and polishing my wife's Pontiac Grand Prix GTP. I switched to Mobil 1 back in the Summer, and I did the 2nd oil change on M1 two weeks ago. I decided to take a peek through the oil filler tube to see how the inside of the engine was looking. I took the cap off, and I noticed a yellowish, foamy or soapy looking substance on the inside of the oil tube. I checked the oil, and it looked fine. The level was still full as well. The first thing I thought about was a blown head gasket. However, the coolant level is still fine, and the car has not been running hot, at least not the last time I drove it on Monday. The film was not on the tube when I changed the oil two weks ago. The only thing I did different was to susbstitute a qt. of 15w50 M1 instead of all 10w30. I did not smell the oil on the dipstick. I wiped the foam off the filler tube, and the oil on the rag I used didn't smell like coolant. It smells a little maybe a little "varnishy" to me. So what do ya'll think the deal is? My wife and I took my car last night, but we plan on driving the GTP today. Yesterday was the first time I've driven the car since Monday, and it was only for a short hop. I really didn't pay any attention to the temp gauge,and the car seemed to run just as well as usual. My wife does know to watch her gauges, but she hasn't said anything about the car running hot or anything. I've only seen this on old sludged up engines before,but this "foam" looks different from that though. This is really puzzling me.