w203 c220 water temp fluctuating

Hi,
i recently had the air con and engine radiators replaced (insurance company provided garage) after hitting a deer on my way home from work in september. After a service in mid november i now notice the water temp gauge fluctuating between just over 60 and just under 80.

my journey to work is 22 miles, takes about an hour and involves local roads for a mile till dual carriageway for 2 miles then motorway for 5 miles, then a & b roads the rest. the car usually reaches temp by the time i'm midway up the motorway and stays constantly at ~80. Now the temp goes upto ~80 by the time i'm midway on the Mway and then plummets to ~60 whilst driving and slowly creeps up towards 80 if i'm sat in traffic not moving. If i have the heater on max the temp plummets again. if i pop the bonnet after my commute, the engine cover and water bottle are not too hot to hold my hand against.
is this an indication that the water pump is having issues following poor radiator replacement?

 

This sounds like an air lock but cannot be, so is the thermostat sticking,,I think that it is

 

Sounds like an airlock to me

 

Take of the filler cap and squeeze the bottom hose many times and see if any air bubbles come up

 

Sonds the same as my 220, which doesn't seem to have any air issues so I'am assuming a thermostat, changing mine next week so will keep you posted.

 

As in my first post then really,,there is nothing else

 

thanks for the speedy responses. i started to unscrew the water bottle cap after a journey this morning (before i posted) and i could hear a fair amount of pressure escaping which seemed dry as i didn't notice any steam or water condensing about the partially opened cap. i've since opened the cap again and squeezed the bottom hose as per Television's suggestion. Didn't see any bubbles but did hear some gurgling after a 20 seconds or so of squeezing. Not had the chance to go on a decent run yet so don't know if this has made any difference.

 

another tried and tested way i use to eliminate air locks is to remove the cap, run the engine, (no need to drive the car) and keep checking the level. run untill all heaters blow hot, temp reads normal and then let it carry on running for a while (till elec fan cuts in on most non MB cars) then switch off and allow to cool. top up when cold and refit cap

 

another vote for defective thrmostat

had same symptos in daughters polo, new t stat, fixed it

 

I had the same prob when i bought my E220, turned out to be defective vicous fan! can you here yours kicking in and out when it reaches temp?

 

thanks for all the responses.
i ran the car for a few minutes with the cap off after a journey on sunday & there was less pressure released when i removed the cap. on my commute this morning, the car only got close to to 80 even though i sat on the m3 in traffic for ages, but i didn't see it drop as much as before even with the heater on max. colbaz, i've not heard the fan kick in at all.
To add to the issue, i've noticed my fuel economy dive to 27 mpg on my commute home, which is worrying. Could it be running a rich mix to try and get warm, will this ruin the glow plugs? no issues starting so assume they are ok at the moment. is the t/valve easy to replace or is it a garage job? any good web resources to research?

 

This still sounds like the thermostat is faulty,the engine should run at over 80c as the thermostat opens at 92c.
Any engine fans do not start until after 92c has been reached