I performed a block test recently to diagnose a problem I'm having. The liquid stayed blue, but I want to clarify I have done this right. The purpose of the test was to see if I could prove a head gasket failure.
After removing some of the coolant using a siphon tool, and placing it in the coolant storage area of the vehicle, I started the engine and tried to test, the coolant level rose and I had to remove more coolant again, but only once.
Then I used fresh test fluid, I placed the test unit over the radiator to create the air-tight seal, and then let the engine run awhile, then I used the bulb to suck air through the test fluid.
The instructions say to do it for 2 minutes. What happened with me was that I apparently sucked out air until there was a negative air pressure, and no more air could be sucked out using that bulb.
So, I did the test once sucking as much air as possible in a short time, and after that, I did it again and paced myself so I could steadily do it for 1½ minutes. I was careful not to let any 'fresh' air into the tube or the radiator. It refused to turn green or yellow.
I did test the fluid itself. The same blue fluid turned yellow when exposed to the exhaust.
- It it normal for this negative air pressure to occur?
- Is it better to remove air quickly, or slow/steady over the course of 2 minutes?
- Supposing there was a blown head gasket, would this negative air pressure still occur?
And of course I welcome additional relevant information such as how this varies between various vehicles, a summary on how to ensure a good test and/or the limits of what this test could prove or disprove.