Quote:
Originally Posted by Jim/TX
I know. That's where I started. I expected any steam formed to condense back to water before it got to the upper tank.
I used the block tester on this engine 10 times now over 6 months, convinced those bubbles mean a bad head gasket. Never once did it turn yellow. (The head gasket is 6 months old, put on after a valve job.)
I made a rubber adapter ring to get a tight seal on the radiator filler neck and I capped off the overflow tube to keep fresh air out. I use a hand vacuum pump to draw the vapor up through the blue fluid for a full 2 minutes.
I do the test with the engine at 1400 RPM, full spark advance, coolant temp 165* (after a long run to get everything good and hot), and a new radiator. You can see the bubbles coming up a steady stream. But the fluid stays blue.
That is how I finally decided that it is steam from some hot spot in the block. As long as it does not foam, I can live with it. The steam just goes out the overflow tube and you have to top up the radiator to replace the water that boils off.
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I wonder if it would be any different with antifreeze?