Several days ago, I had a large coolant leak on my 2000 ML320. The leak originated from the hose which leads to the expansion tank. The coolant was spraying out at the location where the hose connects to the tank. Thinking that a stuck thermostat might be the culprit, I replaced the thermostat. Everything seemed fine for several days, until today I had the same problem. Does anyone have any ideas? The water pump was replaced last year, and the thermostat last week. Could it possibly be the expansion tank valve stuck, or is it a hose issue? Any help would be greatly appreciated.

there is no valve in the expansion tank (the white color tank sits near the firewall underneath the windshield), did you tighten the hose clamps?

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98 ML320 (gone but not forgotten)

Yes, I did tighten the hose clamps. I suppose that I was mistaken about a valve on the expansion tank. For some reason, I thought that there was a valve at the junction between the hose leading to the tank and the tank. Any other ideas besides tightening the clamps?

your problem is quite unusual. the leak usually don't originate from there... did you check if the hoses have cracked at the connection area? or your expansion tank cracked? there is really no other valve or things in that nature in the cooling system other than the thermostat.

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98 ML320 (gone but not forgotten)