Coolant leak diagnosis HELP NEEDED
 

Hoping someone out there can help diagnose a coolant leak we have been battling off and on for a few weeks in our 2003 ES300.



So far we have:



A leak that started some time after we replaced the knock sensors. We did not replace coolant bypass hose at the time because it appeared undamaged.



A few weeks later, a large coolant leak, car overheating, heater element stopped working inside car.



Replaced water pump, timing belt, a/c belt, and power steering belt. Water pump gasket showed signs of wear and being under pressure and we replaced that as well.



Car drove fine for a week and the again leaked coolant and overheating. (Worth noting not as large of a leak as the first instance when water pump went out)



Went through diagnosing and research pointed to thermostat.



Replaced the thermostat.



Lowered car, refilled coolant, warmed up car, began pulling out of driveway when a visible leak started. (At this point we noted the leak coming from near the thermostat)



We have repeatedly checked the oil to ensure no signs of coolant mixing which we understand would indicate a head gasket issue.



Decided based on location of the leak we should go ahead and replace the coolant bypass hose.



Get everything put back together, go to add coolant back in and….you guessed it, it leaked back out. Very slowly but noticeably. A dripping develops as we are filling it. This time, however the leak is on the passenger side, right of center.



Should we be concerned that the newly replaced water pump gasket needs to be replaced again given that the thermostat replacement didn’t solve the leak? Or is it possible that pressure build up before we replaced the thermostat could have damaged the new water pump gasket?



Is there any way to diagnose this issue that we haven’t noted already? Starting to feel like we are going in circles at this point.

TIA

By far the most common failure is the radiator but it sounds like your leak is at that 'stat. Unfortunately it could be the bypass hose as well they love to fail, sometimes suddenly. Is your thermostat housing metal? Sometimes they get replaced with plastic ones.