Just made a 2500 mile trip to Dallas, TX and back. (Medina, OH.) Lot of 100+ degree days. Experienced some coolant loss, no more than a couple ounces a day at the most. Recently replaced timing belt, water pump, both idler pulleys, and lower radiator hose, and thermostat. None of those items appeared to be leaking. Engine runs great, exhaust clean, oil (Valvoline full Synthetic) and coolant (Toyota Red) both looks great. Appreciate any comments, advice, etc.

 

Start with the cheapest things first; try replacing your radiator cap. They can get old & lose effectiveness, opening up & letting off pressure prematurely. Get one from the dealer for under $10 or thereabout.

Or, for around $50 or less, you can get a cooling system pressure tester (Harbor Freight is advertising one for about $49) that will test both the cap and your entire system. FASTEST & most effective way to pinpoint any coolant loss.

 

for sure check fluid level often! I blew up my radiator idling in I-5 traffic a few summers ago; due to a very slow coolant leak that went unchecked, finally hit the point where it overheated.

I carry a gallon of distilled water with me now in my rigs in the event I need to top off.

The pressure tester should tell you what's going on in there though, good first step I would think.