must be a leak cant think of any other way check all joints and manifold incl lambda sensor failing that cracked cylinder head from exhaust valve but i wudda thought the running would be impaired
For some reason the gas is not completely combusting causing water to be expelled in the exhaust pipe.
Generally, with that smell- the heater core has gone bad.
There are 2 of them and they are located toward the front of the exhaust 1 on each pipe coming down from the exhaust manifolds.
Usually in the exhaust pipes coming off the manifolds
Your use of KMh instead of MPH, and that a C180 is not a US model makes me think your speaking of a Euro edition car. Even if it is very similar to the C190 here, the exhaust system is something that is normally a big change for US standards. I can't provide an absolute answer to your problem (although some type of exhaust leak is indicated), but want to make sure you realize that if your getting fumes in (especially at speed), this is a major danger and you should not operate the car. Toxic fumes are probably present and can exfixiate you or at least make you sick or knock you out...all bad things while your driving. This really should be remidied immeadiately.
exhaust gas
if its a rotten egg smell its probably the cat if its loud volume look for a blown gasket or a hole in the pipes
is there any odor..??/ a small leak in the heater core will allow glycol fumes into the cabin.....this would smell sweet.
Also losing coolant i believe. That would most likely be head gaskets. And hopefully only that.
4 exhaust ports
The O2 sensor is in the front of the engine. If you look at the exhaust manifold by the heat shield you will see it. It screws into the exhaust and has a single wire coming out of it running back toward the drivers side of the engine. Easy to change
There is nothing that can cause a gas smell from your heater. There are however a few possible reasons why you experience a gas smell. One could be that fumes from the exhaust are entering the passenger compartment.The other possibility is that your heater could be leaking and what you are smelling is coolant or antifreeze as some people call it. The heater consists of a small radiator and a fan, it circulates hot water from the cooling system through the radiator and the fan blows air through the radiator just like the radiator in front of your car. There is nothing that can cause a gas smell during this process. Check to see if your exhaust system does no have a leak by holding a rag over the tailpipe and get someone to listen at the front. The chances are that the fan is drawing in exhaust gas and circulating themn in the passenger area.