Loosing 1/4 inch of coolant every 3 weeks?

[biscuits and gravy]

I had the same problem once and it was the water filter housing. Slightly cracked at the shutoff valve. There are so many different things it could be though.

When I finally found the dripping coolant it was a very small amount, and I thought it was because the filter was not tight enough. So I tightened the water filter a little more.

It didn't work, I still had to add about 1 size coffee cup of red coolant every few weeks to stay topped off.

Went back with a flash light and looked around more. I decided to change the filter and clean the circular groove out that the water filter gasket seals up against. I did a good job cleaning it and the damn thing still leaked over the next few weeks.

Anyway, went back with the flashlight again and looked up top at the shutoff valve and could see the coolant dribble a few leaks when I pressed down on the bolt head fitting of the shutoff valve.

If your running an APU, go check all those coolant and heater hoses for the APU heating and cooling.