I’m just over 300k on my 98 3.4 taco and have been noticing my coolant reservoir needing to be refilled about every three months. I thought it might be a freeze plug leaking or worse a HG failure because I could not find any signs of leaking coolant. I just kept topping it off and drove it as it ran fine. Turns out my coolant temp sensor had a slow leak for awhile that was not evident up until recently when it started coming out more rapidly. I was actually delighted to finally see the leak and it was an easy fix. It was the original temp sensor. Motor still runs smooth as silk and does not burn any oil.