The car is a 2004 Mercury Grand Marquis GS, 102K. The level of coolant dropped in the reservoir tank in the course of the last three months. It was directly between the min and max cold fill line initially, and a few months later (when it got colder outside), I noticed one morning that the cold level was about half an inch or so below the min cold fill line. So overall, it seems like it dropped about an inch to an inch and a half in three months. No visible leaks, doesn’t overheat. I did one of those oil analysis tests a couple weeks back and it showed it was perfect, but also has 0.2% ethyl glycol contamination.
Is that slow gradual drop over the months, almost imperceptible if you check it every couple weeks, related to the winter temperatures making that water contract inside the tank, or can there be some sort of internal leak? I changed the radiator tank cap with a Motorcraft original one a couple months back, but it’s still doing it. Whet do you think the next step should be?
Do the block leak test.
I just did it. Put blue fluid in the tube until the line, started the engine, removed the cap, inserted the tube opening in the hole, attached the bulb, and pumped it probably 10 times or so. No change in color. I put it in again and pumped it another ten times but in a slower, more deliberate fashion. Took it out, the color started to slowly take on a blue-green tint after about a minute or two. I saw no immediate change in color as I was pumping it either of the times, but after about a minute or two after removing it and observing the liquid, it looked like a blue-green. My instructions on the box say if it turns yellow it indicates a positive for a leak, but it was neither yellow nor did it happen fast. What’s your take on it?
If it turn green, it shows you still have a leak but it is a small leak.
Does it necessarily mean the leak is from the head gasket, or can it be a leak from somewhere else?
Either from the head gasket or fr the block itself. Either way, the headgasket needs to be replaced.