"tobybul" wrote in news: snipped-for-privacy@localhost.talkaboutautos.com:
I had similar problem with a 99 Taurus. Turned out to be a hair line crack in the header/overflow tank. The shop I went to was about ready to replace the engine, they suspected a cracked block as they could find no external trace of a leak. Then one of the older mechanics noticed that the overflow tank had a slightly whitened appearnce at the pint where the plasic mounting met the rest of the tank. Pressure testing did not cause a leak, but vibration and pressure would. solution relaced tank, problem gone.