motoguy128 wrote:
THe blue light would only come back on when driving if the thermostat was stuck open, meaning the engine is too cold. There is a seperate red light indicating the engine is overheating. Although if the temperature light is located on the radiator, a major hose failure could result in a low temp condition, but the huge amounts of steam, and trail of water behind you would be a good sign.
Actually, either of the conditions I described can cause an under temperature reading. In fact, they both happened to the same car of mine... one of my '87.5 Subaru XT's.
I was driving to work, looked down because my heater was going cold, and noticed the temp gauge almost completely flatlined. Looking out the front, there was no indication of what was happening, and by the time I noticed it, almost all the coolant had leaked/vaporized, so there was very little (white) smoke coming out the rear. Pulled over and found that my coolant return hose from the heater core had split, and I lost all the coolant.
After replacing the line and refilling the coolant, I went through some fun "burping" the system over the next couple weeks, including getting a huge air bubble stuck at my t-stat, causing another near-flatline of my temperature gauge.
Incredibly, I didn't warp the heads or blow a HG in either case. I wouldn't reccommend that with any newer engine, as everything made since the mid-90's seems to be hyper sensitive to overheating.