Coolant Loss
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Joined: Sep 2007
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Coolant Loss
Hey Guys,
About a week ago my coolant warning light came on, it was low on coolant so I topped it off and now the reservoir level is dropping slowly. About 18k miles or 3yrs ago I had the water pump replaced and in the past 3-4k miles the coolant was flushed again. Coolant cap replaced too. They performed a pressure check that turned out to be fine. The Head Gasket was done in 98' when it had 38k miles. I checked the coolant and oil with no signs of contamination.
This is what's weird, I have always noticed my car tends to run hot when sitting in traffic whether it be hot or cold out, it will get up to about 100-102c before the fans kick on and the temp slowly gets to about 83c after a few miles of driving. A month ago I noticed it was cooling much better, the car never gets above 90c when idling and instantly drops back down after I start driving. I am a little stumped right now as the car cools itself better but I am losing coolant. I have only checked the visible hose connections to make sure they are tight.
Any ideas where I can start to troubleshoot this issue? Any help would be appreciated!!
1995 C36- 138k miles
About a week ago my coolant warning light came on, it was low on coolant so I topped it off and now the reservoir level is dropping slowly. About 18k miles or 3yrs ago I had the water pump replaced and in the past 3-4k miles the coolant was flushed again. Coolant cap replaced too. They performed a pressure check that turned out to be fine. The Head Gasket was done in 98' when it had 38k miles. I checked the coolant and oil with no signs of contamination.
This is what's weird, I have always noticed my car tends to run hot when sitting in traffic whether it be hot or cold out, it will get up to about 100-102c before the fans kick on and the temp slowly gets to about 83c after a few miles of driving. A month ago I noticed it was cooling much better, the car never gets above 90c when idling and instantly drops back down after I start driving. I am a little stumped right now as the car cools itself better but I am losing coolant. I have only checked the visible hose connections to make sure they are tight.
Any ideas where I can start to troubleshoot this issue? Any help would be appreciated!!
1995 C36- 138k miles
Last edited by RPB; Mar 7, 2015 at 07:20 PM.
Super Member
Joined: Dec 2011
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From: Oregon
'97 c36
I would start by pulling the thermostat and dunk it in boiling water to make sure both sides of the thermostat are working.
Even though you replaced that pump not to long ago I'd still pull the belt and turn the pump by hand and check for any play in the shaft and inspect for wetness around the pump.
Even though you replaced that pump not to long ago I'd still pull the belt and turn the pump by hand and check for any play in the shaft and inspect for wetness around the pump.
Thread Starter
Super Member
Joined: Sep 2007
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I would start by pulling the thermostat and dunk it in boiling water to make sure both sides of the thermostat are working.
Even though you replaced that pump not to long ago I'd still pull the belt and turn the pump by hand and check for any play in the shaft and inspect for wetness around the pump.
Even though you replaced that pump not to long ago I'd still pull the belt and turn the pump by hand and check for any play in the shaft and inspect for wetness around the pump.
Senior Member
Joined: Jul 2010
Posts: 390
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From: San Diego/Escondido, CA
1996 Mercedes C36 AMG
I was in a similar situation.
Mine was replaced a few years back and then the week after I did a fluid flush and t-stat change, the pump started leaking. I just bought a new one and swapped it out.
Mine was replaced a few years back and then the week after I did a fluid flush and t-stat change, the pump started leaking. I just bought a new one and swapped it out.
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MBWorld Fanatic!
Joined: Apr 2005
Posts: 3,784
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From: SCV SoCal
2002 CLK430
The good news is – if it passes a pressure test, radiator hoses, head gasket, and radiator are all usually in the clear. If MB’s have freeze plugs they’re in the clear too. With the usual suspects in the clear, that leaves the radiator cap, reservoir tank, and the water pump. New caps usually rule out half of the suspects . . . . . . . provided the cap isn’t faulty and it has the right pressure rating. Excuse my ignorance on the C36 cooling system, but is the radiator cap on the radiator or the reservoir? If it’s on the reservoir, then I’ll guess the pressure test is performed at the reservoir. If not, is the reservoir dry on the outside? As others have said, the weep hole on the water pump is bone dry with no trace of coolant having been there, right? I know zip about C36 heater hoses, but those should be dry too.
