W204 c320 Cdi radiator fan issue

[Jpderv]

Hi so recently I have noticed that my c320 has a temperature issue in that it gets hot I'm in stop start traffic or not we to move fast enough to get the air going through the heater to cool it down it goes up to about a 100c I randomly get a water temp symbol appearing on the information display even when temp is around 85/90c.

I pulled in to day when the temperature had risen to 100c didn't turn off the car but loosened the expansion bottle top carefully as I knew it was rosten the moment I loosened it and heard a little his the radiator fan sprung into life it's happened twice since this morning and same on every occasion as soon as I loosened the expansion bottle top the fan kicked in and the temp dropped.

I've been trying to find some info on this all day and I haven't been able to find another person with the same issue.

Has anyone got any ideas what it could be?

Thanks in advance.

 

[wu56Shoozz]

Yup!

1. Thermostat

2. Water Pump

3 Disconnect the radiator both top & bottom hoses and flush with a garden hose. Run until crystal clear water appears, and reverse flush. Then with the nose of the car in the air (front wheels off the ground) and heater controls set to hot refill via the Top Hose only.. and fill until water appears out of the radiator then connect. Run up to temp and test.

Try the above before going any further and report back. I'd go for No1 personally..

 

[Auto-mobile]

Mercedes are only classed as overheating if they exceed 98c, get the fault codes checked as fan units log a fault, you could also monitor the coolant temp exactly on diagnostic machine also.

It could be a sticky thermostat, water pump will eith work or not, if it doesn't work you will just overheat.

 

[markjay]

By loosening the expansion bottle cap, you have depressurised the cooling system and allowed the coolant to boil over. This will immediately raise the coolant temperature and might be the reason why the fan springs to life.

Alternatively, what I have seen in the past (not on Mercs), is that if there's air trapped in the coolant system , it tends to accumulate at the top part, and if the temp sender happens to be there, then the fan relay might not activate the fan because the air does not conduct the heat to the sender copper plunge very efficiently. Keeping in mind that some cars have more than one sender, i.e. the temp sender for the gauge is not always the same as the temp sender for the engine ECU, and while the gauge 'knows' the engine is hot, the ECU does not.

 

[Jpderv]

Thanks for all the suggestions folks much appreciated they all seem plausible to me what I'm gonna do first is try what wu56Shoozz said first and see how I get on I hope to god the head gasket isn't the issue I have a little gadget from a few years ago that goes in the expansion tank with blue fluid in it kind of looks like a science laboratory gadget will do that test aswell.

Am I Wright in thinking that the only diagnostics equipment that is really any good for Mercedes is star? As I'm not aware of anyone in my area that has something like that or would regular hand held diagnostics machine be able to tell me temps and relavant DTCs


@Auto-mobile it makes sense now that the fan only come on when I loosened the cap if that makes the water boil 98c seems like a high temp to bring on the fan though, now that you mention that I don't think the gauge actually got over 100c it was around that or maybe a smidge lower.

Anyone ever had there merc get near a 100c maybe it's nothing to worry about at all lol.

 

[Auto-mobile]

maybe it's nothing to worry about at all lol.

I don't very much the head gasket has gone.

 

[Jpderv]

I'm sure it's probly fine to its just the first expensive car I've owned any we niggle I always tend to think the worst lol.

 

[pembssurf]

I'm sure it's probly fine to its just the first expensive car I've owned any we niggle I always tend to think the worst lol.

Head gaskets going are not really a thing that goes on new cars these days. That's not because they are any better or worse than in the head gasket failure heady years on the 70/80/90's but cars generally have much more expensive things that go bang causing the car to be a write off long before head gasket issues surface.

I remember my first 3 cars all being late 80's used cars all having head gaskets go at some point or other. Apart from cam belts letting go these were the top two big repair jobs done in the day and what all owners used to be afraid of. Now it's DPF's, turbo failures and Cam chains (M271 engines I'm looking at you)