Temperature up and down on C36

[mickl]

When driving back from work today I was stuck in a traffic jam for about 40mins.

The temperature gauge (usually around the 87-90c mark) went up, was over 100C at one point, all quick rapidly in the space of a few mins. Fearing things about to go pop I cranked the heater onto max and the temperature immediately dropped back down to 87-90c. Once I started moving everything was back to normal. When I got back home I stopped and let the car idle for a little while to see if it crept back up which it did. I've checked the coolant levels and the radiator fan to see if it was working and all seems fine.

Anyone any suggestions as to a cause and if it's potentially expensive? :? It's had a B service recently and a note on the service book was 'antifreeze ok'.

 

[Myros]

hot AMG 36

My C280 can do this in traffic, and so did my BMW and my Alfa. It's one of those Star Trek "canna change the laws of physics things". All down to not enough airflow through the radiator, regardless of the fan(s) working away like trojans. Also , there isn't much water flow at idle speeds. If you can save up a bit of gap when the traffic moves, try pootling along in 1st with revs up over 2000 rpm. That should stir the water up a bit. You could also give the engine the odd rev up if stationary. Getting the windows down and the heater on also helps, as you said. If you can see you are going nowhere, engine off is the best way to avoid it. Tricky in our traffic jams, espec if you are behiond a lorry and can't see what is happening ahead. If you can for see no movement for the next thirty seconds or so , I'd be thinking of engine off from a fuel-saving point of view as well.

 

[mickl]

it just worried me that the gauge moved that fast in such a short space of time. My last car, a VW Passat which has sat in 2hrs of London traffic without a murmur on the gauge. I didn't wait to see if a fan did kick in as the speed the temp was rising very fast.

I'm shocked that the gauge bounces up and down that much, especially on a Mercedes. It's not really acceptable for a car like this where you have to crank the window down and whack the heater up when an ordinary repmobile doesn't require this.

 

[Myros]

worried AMG

I've noticed it happens much more quickly if I've been shifting along at a reasonable rate, and generated more heat which hasn't had a chance to be wasted. I t also happens if I'm stop-starting in town.
You are right to be concerned though, as it doesn't take much to ti[p the balance. Last week was pretty hot, and that must have contributed to the build-up of heat in your engine bay. Are you getting any squealing/slipping drive belt noises.
I had an oil temp gauge in my old BMW and it was frightening to watch that shoot up first, then a corresponding rise in the water temp would follow. The M104 engined mercs do have that oil-cooler/coolant interface which makes them so quick to warm up. Maybe that is a contributory factor to the traffic jam brew-up.

 

[justin1820]

this engine has a viscous fan on it so it is engine speed related, firstly you cant always beleive the accuracy of the gauge on the dash and water does not boil until about 106 degrees under pressure and with antifreeze, i wouldnt worry about it to much unless it goes dramatically above 100 degrees.
ps. if you had the air con on this will make the engine work harder and the condensor will also make the radiator hotter

 

[mickl]

thanks for the replies. Hopefully it's all ok. It's just I don't expect this from a Mercedes. My previous car, a VW Passat never had anything like this, even with sitting in hours of London traffice jams.

 

[flyingtech55]

Hi Mick1

The reason the temperature gauge goes up and down rapidly on a Mercedes is because its a 'proper' gauge and gives an accurate indication of the engine temperature on a real time basis. Its rapid movement is an indication of its good quality not the reverse as you and some of the other respondents are implying. Repmobile gauges are, generally speaking, simply indicators of the temperature and are, by virtue of their operation, heavily damped. It should not be necessary to wind down the windows, put heater on etc on any modern car to maintain the temperatue within the appropriate limits Mercedes included. If you have been driving quickly and then sit idling then the temperature will be seem to rise quickly due to the fast acting gauge (not seen on a heavily damped 'repmobile' gauge) and is because the engine has to dissipate the heat energy contained within the core. Provided the temperate does not exceed about 105 then all is well.

I respectfully wish to disagree with the chap who said Merc. gauges are inaccurate. On the contrary I have found them to be very accurate; but they do reflect what is actually happening in the engine on a real time basis. Repmobile type car gauges are simply indicators not gauges. This is done for two reasons; indicators are cheaper than proper gauges and secondly, indicators smooth out the peaks and troughs of the engine temperature and indicate an average temperature to prevent the driver getting over excited about seeing the temperatue fluctuating while driving. If you watch carefully, once the temperature has stabilised while idling if you then start driving fast the temperature will actually drop below normal until the fans, stat. etc adjust themselves for the increased flow through the radiator and engine bay.

Hope this helps.

Gliderman

 

[mickl]

thanks for the reply flyingtech55

I'll just have to let the temp rise next time to see if the fan does kick in. Thing was I hadn't been driving it hard before sitting in traffic. I'll see how it goes.

I've been told the thermostat might be a culprit. Is this an easily changeable part, bearing in mind I'm not too mechanically minded?

 

[flyingtech55]

Mick1

I don't know the engine in your car but the stat. in my 190E was very easy to change (M102 engine I think) but bear in mind that it is a spanner job. A job that I and some of the other chaps (and chapesses) find straightforward may not be so to others. You will have to judge whether you have the knowledge/experience to do it yourself. Stats. are generally designed to fail open and the symptom of my stat. failing was that the engine rarely achieved the correct running temperature (too cool). Also there was excessive temperature variation when the temperature should have stabilised. It's a bit difficult to describe that bit but I knew the cause from experience I suppose. The stat. was pretty cheap even from the Stealership. Stats. are a quite a common fault and should be renewed periodically anyway. If in any doubt stick in a new one.

Hope this helps