Mysterious loss of coolant....looking for ideas please
So I'm looking for a list of things to check.......I'm currently losing coolant at a rate of about 2-4 ounces every 100-150 miles. Essentially if I top it off at the lower mark on the expansion tank indicator, after 100 miles or so it has sunk down so the top is flush with the lip of the tank.
1. I pressure tested (cold/cool engine) and no loss of pressure at 15psi.
2. Looked for stains and cant find anything anywhere of significance.
3. Its not getting worse, a stable rate of loss so far.
4. Only cooling related issues- water pump was replaced about 5K miles ago, and a couple weeks ago I replaced coolant and inspected for any indications of leaking. The 04 ZHP has about 64K total.
I'm thinking perhaps to pressure test when its hot, but that would entail hooking up the pressure tester when cool and getting it hot I assume?
The coolant tank cap is original AFAIK, might replace that but I dont see stains around that. Hoses all look good and no evidence of leakage, but I know at some point soon I know I need to do the major cooling system overhaul, but I want to know the offending part first.
What else to do?.......I dont want to have a small leak suddenly turn into a gusher at a bad time for obvious reasons so trying to get to the bottom of this.
Tim