Water Temp 500sl M109

[mycos]

Hi,

I have a 93 500sl M109 engine and just wondering what temp should the guage read as mine seams to be up and down between 60 and just above 80. Is this normal or should it be rock steady.

Any comments would be appreciated.

Thanks

Mike:?

 

[television]

The gauge should not move suddenly from 60c to 80c a gradual change is ok

 

[mycos]

Hi Malcolm,

Thanks for the quick response, It's not that it jumps around it just doesn't seam to find a steady point under normal driving conditions. I'm thinking that the thermostat could be on it's way out and jaming open? I would say it runs cold unless i'm giving it some, also being that it's cold outside and i've got the heaters on.

Thanks

Mike

 

[television]

A flickering gauge could be the sender, though the thermostat could be faulty that would not make it move around, the thermostat cant affect the engine that quickly and it would be a gentle cooling or warming

 

[mycos]

I would say it's more of a gentle cooling and warming rather than flicking. I'll run it at the weekend on a high tickover to see if the fans come on and at what point on the guage. How high should i let it get if the fans don't come on? Might be worth checking for cold spots on the radiator? Just another query what colour is the antifreeze / coolant that mercedes use?

Thanks

Mike

 

[television]

Cars with a visco fans come on at 80c, cars with electric fans come on at 100c

 

[wireman]

The water should be somewhere near 90C, if your stat is missbehaving it is quite feasable that the temp could dramaticaly rise (if the thing slams shut) at a rate noticable on the gauge, it is normal for the cooling system to over pressurise and blow off steam if this occurs. If the stat is stuck open it will take all day to get up to anything like hot. if the stat is stuck part open it may run cooler but will run hotter when you give the engine some work to do.

Methinks your gauge may be faulty, the sensor in the head being a likely culprit if your fuel gauge is steady (perhaps just a bad connection to its stud), and the intrument regulator if they both wander.

But if the stat is old it may be the culprit and its worth changing it when you next replace the coolant, at 2 year intervals is the MB reccomendation on the 124 (50/50 AF&water). The temperature on the stat is the temperature at which it begins to open, it is normal that it takes another 10 or so degrees to fully open up.

 

[mycos]

I think your comment "if the stat is stuck part open it may run cooler but will run hotter when you give the engine some work to do." seams about right as the temp does reflect driving style albeit excessively.

I have the bills for what looks like all work done since new and there is no reference to a thermostat being changed. It also had a clean bill of health from Mercedes main dealer in October when last serviced.

As it's 16 years old done 98k, for the sake of £?? for a stat I’ll change it over. It looks a fairly straight forward job is there anything I should be aware of like bleeding air from the system or flushing radiator?

Where the best place to buy these sort of serviceable parts?

Thanks in advance

Mike

 

[television]

Nothing to bleed as the system is self bleeding, you need only drain enough water to clear the thermostat level

 

[mycos]

Thank you Malcolm,

 

[mycos]

Hi,

Just changed the thermostat and now the gauge sits just above the 80C, within 5 mins of starting.

So thank you for the guidance.

Mike

 

[television]

Hi,

Just changed the thermostat and now the gauge sits just above the 80C, within 5 mins of starting.

So thank you for the guidance.

Mike

Thats good news and thanks for posting back with your fix.

It was a little puzzling to start with