Team MightyBoy

I am loosing water from the coolant reservoir after driving every 120 km, there were traces of coolant on the battery terminals as well as the bonet itself, I have checked the gasket, it was all ok infact i get it checked from various people and they all were positive about it. There were no oil traces in the cooling system, Although i noticed that a slight leak might be possible from the mechanical thermostat seal but can it affect the cooling system this badly that it throws out the water from the coolant reservoir. Also please let me know the correct way to bleed the system. 1 more thing i like to add if i drive rashly water comes out way too quick from the reservoir like say 3 to 4 km.

One key question: Is there a pool of coolant left when it is parked?
YES - the problem is an external leak. NO - leaking head gasket
External leaks can come from a dud water pump, cracked hoses or radiator end tank, or corrosion in anything that is metal. Just a matter of giving the engine bay a good clean and looking for the source.

The problem could also be as simple as a dud radiator cap or engine running too hot and pumping the coolant out.

Very simple system to bleed. Fill your radiator with the engine cold, leave the cap off for now. Start the engine (ensure Park/Neutral & handbrake on) & watch the coolant level in the radiator - once the engine makes operating temp & the thermostat opens, the coolant will be circulated & pushed into the voids not filled. Air will be pushed out via the radiator, the level will drop. Top the radiator up until the air stops coming out, put the cap back on & the level should be normalised via the expansion/overflow tank.

Well explained Gadj. Also worth mentioning that unlike other engines the highest point of an MB cooling system is the radiator cap, which is why it is so easy to bleed.

Don't forget to have the interior temp set to hot. That will ensure the heater core is bled.

Thank you guys, you guys are the best (Y) (Y) (Y). I found out the leak, it was the gasket/seal for mechanical thermostat, which was leaking, when i opened up, the seal was to none. After replacing it, water stays where it suppose too plus i forgot to bleed the system when i changed the seal. car is running awesome, Thanks Alot,

1 more thing some mechanic/technician here told me to get rid of this mechanical thermostat as he suggests that that he was worth when the engine is new plus back in 90s It was required, however due to climate change, here in karachi its about 40 to 42 degree max so do you think i should listen to him, my car has done 160k km in the last 10 years, do you think i should remove it ?

Absolutely not - you will be back to him with another problem soon after removing it. Part of the thermostats job is to slow the flow of coolant so it has a chance to be cooled as it passes through the radiator. Remove the thermostat completely & the coolant speed increases thus reducing the radiators efficacy. The other, temperature sensing valve part can be removed as a last resort to keep you going but the limiting plate must be put back in. The valve would have to be cut free to remove it. The valve is there to get the engine to operating temp quickly which gets the engine running at peak efficiency.

thanks alot gadj

if the thermostate has a little joggler pin in it just cut that off it will help keep water flowing a little more freely and easier to bleed the system because you dont have to wait as long for the thermostate to open