Overheat and High Coolant Presure
Thread Starter
Junior Member
Joined: Mar 2008
Posts: 46
Likes: 3
ML350 '06, SLK55 '05, C280 '97
Overheat and High Coolant Presure
Hey my old C280 started to misbehave today. coolant got purged from tank. I though thermostat got stuck so i replaced it but no luck. Here are symptomps
- temps rising fast (but not to critical point... ) i'm still getting 90-110C temps
- pressure of the top radiator hose is so high i cant squeeze it any more
- driver side of the radiator, pump, thermostat area super hot
- front radiator is cool
- antifreeze tank is cool
Feels like circulation issue. Should u replace pump next? Or what could it be? Last week I got belt replaces as old one felt apart , maybe some home radiator line got squeezed or clogged some how?
Any ideas?
- temps rising fast (but not to critical point... ) i'm still getting 90-110C temps
- pressure of the top radiator hose is so high i cant squeeze it any more
- driver side of the radiator, pump, thermostat area super hot
- front radiator is cool
- antifreeze tank is cool
Feels like circulation issue. Should u replace pump next? Or what could it be? Last week I got belt replaces as old one felt apart , maybe some home radiator line got squeezed or clogged some how?
Any ideas?
MBWorld Fanatic!
Joined: Nov 2015
Posts: 1,456
Likes: 140
From: Westcoast/Interior
02w163ML500 / 97w210E50AMG / 99w202C230k / 95w124500e-wip
Hey my old C280 started to misbehave today. coolant got purged from tank. I though thermostat got stuck so i replaced it but no luck. Here are symptomps
- temps rising fast (but not to critical point... ) i'm still getting 90-110C temps
- pressure of the top radiator hose is so high i cant squeeze it any more
- driver side of the radiator, pump, thermostat area super hot
- front radiator is cool
- antifreeze tank is cool
Feels like circulation issue. Should u replace pump next? Or what could it be? Last week I got belt replaces as old one felt apart , maybe some home radiator line got squeezed or clogged some how?
Any ideas?
- temps rising fast (but not to critical point... ) i'm still getting 90-110C temps
- pressure of the top radiator hose is so high i cant squeeze it any more
- driver side of the radiator, pump, thermostat area super hot
- front radiator is cool
- antifreeze tank is cool
Feels like circulation issue. Should u replace pump next? Or what could it be? Last week I got belt replaces as old one felt apart , maybe some home radiator line got squeezed or clogged some how?
Any ideas?
While the engine is running, unplug the sensor (easy to do) and the fans should switch on.
If the fans do come on with this test, then change the temperature sensor and see if this works.
Thread Starter
Junior Member
Joined: Mar 2008
Posts: 46
Likes: 3
ML350 '06, SLK55 '05, C280 '97
yea there is something that looks like sensor on thermostat. Though main fun is mechanical. 2 Aux fans are electric. If its mechanical fun it can be clutch but why im kinda not fully leaning towards fan idea is that coolant tank is not hot. In my understanding if if there is circulation in close system then all parts of the system should have equal temperature. What im getting is area around thermostat (well engine outlet) super hot, like even chassis frame is so hot i cant touch it while liquid tank not getting any hot fluid in there. Yet im not sure about pump as there are no noise coming from it, but to be fair this is not original pump its aftermarket replaced i guess like 17 years ago
Thread Starter
Junior Member
Joined: Mar 2008
Posts: 46
Likes: 3
ML350 '06, SLK55 '05, C280 '97
little update, after testing on highway for 30 miles, getting good low temps on highway but as soon as hit traffic going to 100C easy, and now coolant tank is hot too, yet hoses are under high pressure 
Junior Member
Joined: Dec 2017
Posts: 46
Likes: 9
1999 C230K
It does sound like a water pump, especially since you replaced the thermostat. From cold to hot, with the car parked and idling, heater on and pressure cap off, does the upper hose near the radiator suddenly get very hot at about 70c, or a little over, meaning the pumps working and the thermostat is opening? Does the heater get very hot? Even at idle it should still put out quite a bit of heat if the system is working. With the pressure cap still off, you should be able to, wearing gloves, squeeze the upper hose, rev the engine a bit, and feel some water pulsing through the hose. Does the lower hose collapse? You can really notice this by revving the engine while looking at the hose.
The only other thing I can think of is a plugged radiator, since you're overheating only in traffic. When checking your radiator's heat, did you find any areas with a noticeable temperature difference?
The only other thing I can think of is a plugged radiator, since you're overheating only in traffic. When checking your radiator's heat, did you find any areas with a noticeable temperature difference?
