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antifreeze leaking through cap when car warms up

1469 Views 7 Replies 3 Participants Last post by  zoltandy
Guys I need your help. I have a 2000 C 280 Sport with about 51,000 miles on it. It seems that when car is driven at slower speeds and in traffic, it pushes the anitfreeze out through the cap and starts to run hot (the guage moves past the middle into the red). On the highway it is fine and it operates at the normal temp (in the middle). I also noticed that the upper radiator hose has plenty of pressure (almost to much) and it is very hot, however the lower radiator hose is only luke warm. None of the hoses seem to be leaking, nor is the water pump. The only visible leak is through the radiator cap when the pressure increases past the middle on the guage. Has this happened to anyone else?

I am hoping it is something cheap like a thermostat or fan switch. Any suggestions?
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I just inspected a bit further. It seems that it is not leaking from the cap but from the overflow. I also noticed that the bottow hose has finally warmed up. At what temperature is the fan required to turn on, mine is not turning on past 80. Is there a fan switch that goes bad? I checked the fuse and it is fine.
Help, antifreeze leaking through cap when car warms up

Guys, I need your help because my car is sitting the garage laughing[:eek:)]at me while I drive a back up P.O.S.[B)] The more I research this, the more it leads me to believe that the fan is the culprit. When is that fan supposed to turn on and how do I test it?
I checked the cap, but it is not leaking from there. However, the overflow hose that is on the reserve container is spewing out the antifreeze when the car heats up. Also the fan is not turning on no matter what the temp is. Where is the fan switch located on the engine? I put power to the fan to test the fan motor and it is working, so now I want locate the thermal switch. Any input on the location of this switch would be greatly appreciated. Thank you for your feedback and I will still replace the cap to be on the safe side.
I am back and just wanted to let everyone know that the problem was the engine fan control unit. It was about $300.00 in parts and labor.
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