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The only brand of expansion tank and cap to buy is Modine and only Modine! The installation of aftermarket cooling system parts is strictly verboten.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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The expansion tank photo you posted is indeed missing the lower (one of two) O Rings.
However the end of the cap is melted. From excessive heat/steam. (We see this a lot)

So the question becomes (chicken or the egg) what happened first?

Was the cap bad, you continued to loose coolant until an overheating type of situation happened and the steam melted the cap? Into complete failure.

Is there an issue with the cooling system and the car overheats, eating the cap and you can't keep it cool because of the root cause AND the (now) bad cap?
 

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2002 E46 320 se tourer
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Mr car is right your definitely missing an o ring
I had the same problem with my cap bought a new one only to realise that I only needed the o ring
 

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Discussion Starter #9
The expansion tank photo you posted is indeed missing the lower (one of two) O Rings.
However the end of the cap is melted. From excessive heat/steam. (We see this a lot)

So the question becomes (chicken or the egg) what happened first?

Was the cap bad, you continued to loose coolant until an overheating type of situation happened and the steam melted the cap? Into complete failure.

Is there an issue with the cooling system and the car overheats, eating the cap and you can't keep it cool because of the root cause AND the (now) bad cap?
I'm more than positive. The radiator switch stopped working. Causing excessive heat to combust the expansion tank. I've orderd a new kit for cooling from ecs. Should be here in a few days. All hoses will be changed. Along with the switch and tank
 

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I see something disturbing but it may be a trick of the light. Are there small pieces of clear plastic film on the cap? If so, those may be pieces of your head gasket, which is a laminate of many layers.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Lets not freak him out.
Looks like threads from a used rag.
 

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Discussion Starter #12
Yeah I used a rag to wipe the cap. Around the the threads. But what I find scary is chips of plastic from the cap are missing. Noticed them also in the top expansion tank hose?.. cause of concern? For possible damage to the engine itself?
I see something disturbing but it may be a trick of the light. Are there small pieces of clear plastic film on the cap? If so, those may be pieces of your head gasket, which is a laminate of many layers.
 

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Discussion Starter #13
The expansion tank photo you posted is indeed missing the lower (one of two) O Rings.
However the end of the cap is melted. From excessive heat/steam. (We see this a lot)

So the question becomes (chicken or the egg) what happened first?

Was the cap bad, you continued to loose coolant until an overheating type of situation happened and the steam melted the cap? Into complete failure.

Is there an issue with the cooling system and the car overheats, eating the cap and you can't keep it cool because of the root cause AND the (now) bad cap?
I'm more than positive it's a bad cap. Which led to excessive heat. Then to the expansion tank itself. Better than anything to just change. The switch. The hoses and tank. All in one go
 

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Discussion Starter #14
I'm more than positive it's a bad cap. Which led to excessive heat. Then to the expansion tank itself. Better than anything to just change. The switch. The hoses and tank. All in one go
But also I think the switch may have stopped first. and made the cap get severely hot..to melting point. Terraphantm is gonna be the best bet after this..
 

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Is the “switch” your talking about the temperature sensor in the lower radiator hose? It’s actually a thermistor, a resistor that changes resistance as its temperature changes. It’s a “negative coefficient” thermistor which means it’s electrical resistance goes down as its temperature goes up. Basically, the engine computer (DME) measures the voltage drop across the sensor. As the voltage drop decreases the DME knows the temperature of the coolant leaving the radiator is increasing. At some temperature it turns on the electric fan.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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NTC in BMW speak. (Negative Temperature Coefficient) Most temperature sensors used in BMW's are refereed to as NTC in wiring diagrams and FUB documents.
There was a time that they also used PTC sensors.... IIRC the heated washer jet heaters are of the PTC design.
 

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Discussion Starter #17
NTC in BMW speak. (Negative Temperature Coefficient) Most temperature sensors used in BMW's are refereed to as NTC in wiring diagrams and FUB documents.
There was a time that they also used PTC sensors.... IIRC the heated washer jet heaters are of the PTC design.
Yeah...you guys are speaking Japanese..i dont claim to know all but you guys seem to know what your talking about lol
 
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