Yidney

I'm in the process of trying to track down one of those mystery coolant leaks where the level in the expansion tank goes down slowly but no sign of a leak. I need to investigate the water pump more closely. But for the moment I have a different question. Cold, the level is about two inches below the top of the clear part of the expansion tank. But hot, the tank is still full. So if I added enough to fill the tank when cold, where does that extra coolant go when hot? Is it all in the same space, but just under more pressure? It's not easy to compress fluids, so I was just curious how more coolant fits in the same sealed system.

Rudeney

The pressure increases. Boyle's Law in practice.

gaazmon

I've started to have the same issue with my vehicle recently

Rudeney

Common leak spots are the coolant pump, the overflow hose nipple on the tank, and the tank itself. When the pump seal leaks, it's hard to see because it evaporates on the hot engine block, plus it's hidden behind the pulley. When the tank or nipple leaks, you should see some signs in the area. It can sometimes look like it's spayed on the tank, but that's because the air flow throws it all around.

Yidney

Today I tried to see if I could find the source of my mystery coolant leak. Definitely not the expansion tank. I also saw no trace of dried coolant or leaking at any hose connection. That basically left the water pump. Nothing obvious, except I took a dental mirror and put it behind the pulley and used a strong led flashlight. The backside of the pulley near the end of the pump shaft was strangely clean. As was an outer ring where the pulley shape undulates a bit. They were as clean and shiny as the day they were installed in 2008. Other areas inside the pulley had the typical grime layer. I figure only some liquid could keep those areas virgin clean. Since I'm doing the belt anyway just for the heck of it, I have ordered a pump as well.

gaazmon

Yup mine was on that hose nipple that comes out the tank. The hose that goes over it was fine, but after loosening and pulling the hose off, the smaller hose nipple underneath was torn and leaking fluid once hot. I just had the whole coolant tank replaced.