E420 MB defective cabin heating system causing overheating

AFAIK, only way that could happen would be if the defect was a leak that resulted in a loss of coolant.

Yes, but it's only flowing when the air needs to be heated. In summer, for example, it's off and the car doesn't overheat because the heat gets dispersed by the radiator.

If it was stuck, you could have a cold cabin or a ver hot cabin. But you would not have the engine overheating.

Perhaps someone else can help you out on that specific model. In general for almost all cars, setting cabin system to max heat and just driving will vent the air.

How did you check the thermostat? Either the thermostat or a blocked radiator would be the suspects. Also, though less common, could be a radiator hose that collapses when the engine is running.

You're not very specific, your car heats up to what degree? and what brings you to conclusion that it's over heating after you checked everything appears normal to you?

You did report overheating back in November. Is it the same symptom? Is the reservoir filled up after heated up? It sounds to me there is air going into the system. The air trapped in the heater usually can be bleed by full heat setting while running the engine (provided water pump is good and duct is not clogged). Trapped air will not expand because the whole cooling system is pressurized. However, exhaust is hot and high pressure. A blown head gasket sounds a possibility, which Tiger mentioned before.

Derf-E420-94 wrote:

I removed thermostat and placed it into cooking pan filled with water, heated and watched thermostat open up at 80c...

There's a tiny vent hole with tiny ball bearing check valve, on one side the base plate of thermostat. What is the correct orientation of that vent? I have it positioned on top when I installed thermostat. Is that correct or not... Help

Yes

Heater valve... monovalve

Usually I squeeze the upper radiator hose until it fills up with fluid and the system will do the rest.

Checking radiator cap means nothing. I believe you got air in the system and at what temperature do your gauge read?

Air in his coolant system? Not to worry, the pump will work thing out eventually new coolant from a reservoir will fill the air space.

richard ha scritto:

I do not know the specific car cooling circuit, but what you say, Richard, is not always true. As a matter of fact, very well hidden, but some cooling circuits have valves placed in specific points to help removing air bubbles from them. It's usually located on top of the internal radiator (the one used to heat air in the car) and sometimes it looks very similar to a tyre valve. Our friend should look for a repair manual if he wants to check this point on its own. OR ask professional advice.

I can remember once upon a time the user manual reported procedures not very... user related! as checking valves, changing fluids and so on. But nowadays... They hardly write the tyre pressure suggested! But they are filled up with useless hints as: "If you drive slowly you'll save gas and contribute to a more healthy environment"....

Even if such an air release valve exists on the heater core, how the hell is anyone supposed to be able to get to it? The heater core is about the last thing you ever want to have to get to in a car. I've never seen such a venting valve in a car.

Mercedes-Benz 1999 to present should behave the same thermal conductance system.

If you believe the air is there, you got to help the pump with its circulation since the thermostant doesn't kick in at low temperature(below 80C). To find out whether the air is there or not, check the upper tube, if it's tight and smelling, then there is No air in there.

Derf could have other problems besides the pump, a pump usually doesn't go bad easily. He could have frictions in his brakes, or friction in the pump itself, if he bought a rebuilt pump, I can guarantee you that he got a bad rebuilt part. How do I know this? I went through the whole inventory of autosupply companies to check them out physically myself. Don't believe the sellers, they lied to get your money. I learn this the hard way, by paying Optimum Fuel Systems to find out for me, then I learned it through them.

Mercedes-Benz 1999 to present should behave the same thermal conductance system.

If you believe the air is there, you got to help the pump with its circulation since the thermostant doesn't kick in at low temperature(below 80C). To find out whether the air is there or not, check the upper tube, if it's tight and swelling, then there is No air in there.

Derf could have other problems besides the pump, a pump usually doesn't go bad easily. He could have frictions in his brakes, or friction in the pump itself, if he bought a rebuilt pump, I can guarantee you that he got a bad rebuilt part. How do I know this? I went through the whole inventory of autosupply companies to check them out physically myself. Don't believe the sellers, they lied to get your money. I learn this the hard way, by paying Optimum Fuel Systems to find out for me, then I learned it through them.

Friction in the brakes causing an engine to overheat?

Friction in the pump? Even if the pump has some friction, which would be a bad thing, it would still pump water, no?

Here's a question. Has anyone ever seen a water pump fail in a mode where it won't pump water? The ones I've seen fail by LEAKING. For it to fail to pump water, I guess somehow the impeller could come loose from the shaft or have disintegrated from corrosion. Just curious, has anyone seen this actually happen?

I have seen plastic impeller falling apart and stop pumping. The blades looked like eaten by rodent and what was left was just a flat plate. Though the few pumps I have seen in recent years were all made of metal.

snipped-for-privacy@> Here's a question. Has anyone ever seen a water pump fail in a mode

If overheating is cause by head problems, how can I check whether it's a cracked head or blown head gasket (are there checks for both)? Also, I replaced my coolant with Zerex G05 and not MB brand... could that be a problem? If coolant is overheated do I need to replace it?

Thanks, Derf

It is easy to determine if you got a cracked head. There is a simple dye test where you extract some coolant and put a dye in it. It will change color when it react with CO.

I hear it all the time on BMWs... not Mercedes.