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As you probably realise, the intercooler on these cars is a water /air type. The plug is to bleed the air out of, or to help fill the intercooler water jacket. This is necessary even though it is connected to the expansion tank. Mine had been left full of air after the garage which sold me my car changed the thermostat before purchase. Maybe worth opening it (when cold) and checking that you can see coolant in it and if not top it up slowly.
Thanks John
I undid the cover and checked the coolant, it was not at the top so I added some, maybe half a litre, then it started to flow into the reservoir which is now full above the max mark so it was not possible to completely fill the intercooler to the top of the hole. I hope the core is full when the level is at the bottom of that inspection hole.
I had been intending to pull off a hose to check the intercooler coolant pump is working so pic before filling
I thought maybe while the intercooler inspection cap was off I might be able to see coolant flowing inside. I switched on the ignition and could hear the pump whirring (after disconnecting the fans) but no sign of coolant flow. Maybe the pump impeller is broken?
That's what the level looks like in mine, and I couldn't see any movement with the ignition on and the pump whirring ether. Does anyone know if you should be able to see the water circulating? I would have thought so.
a new intercooler pump is an easy upgrade/peace-of-mind exercise
Having said this, I got my mechanic to fit it!
I bought the Bosch one with the -002 suffix as per other forum posts
Make sure it comes with the plug adaptor
My mechanic used an old coil clamp to fix it, as it is slightly larger in diameter than the old Hella one
Well, I pulled out the pump and it pumps water ok, plenty of flow while not attached to any hoses, but low pressure. If I put my finger over the outlet it is very easy to stop the water. I guess this is normal, all it needs to do is circulate the coolant.
I pulled off the hose which feeds coolant to the intercooler and you can see why there was no flow evident (the green coolant is in the intercooler outlet stub, the "in" pipe is the stub on the left):
Well, I pulled out the pump and it pumps water ok, plenty of flow while not attached to any hoses, but low pressure. If I put my finger over the outlet it is very easy to stop the water. I guess this is normal, all it needs to do is circulate the coolant.
I pulled off the hose which feeds coolant to the intercooler and you can see why there was no flow evident (the green coolant is in the intercooler outlet stub, the "in" pipe is the stub on the left):
Well I guess THAT would do it!
....soooo what the heck happened, what is plugging up the hole?
A new and better higher flow Bosch pump (do a search here in the X300 or X308 or X100 forum for the right part#) is only about $100 as I recall, so this might be a good time to clean out the intercooler and upgrade your coolant circulation.
You could try back flushing it with a garden hose and mains water pressure, which is much higher than any pump will deliver, assuming you live somewhere with decent mains water pressure.
When I replaced my dead intercooler pump with one of the higher capacity bosch pumps, I had very strong flow out of that port. Definitely a very good investment.
I cleaned out the gunk which appeared to only be in that inlet stub, then I back-flushed the intercooler and the radiator. I used a garden hose but limited the pressure so there was less risk of rupturing the intercooler or radiator. A bit of gunk came out and the water flowed easily so I am hoping that the intercooler and radiator are not partially blocked. I think the gunk grew due to a chemical reaction at the (probably) zinc-plated steel inlet stub.
A short drive went well, intake air temp about 14deg C above ambient.
Forgot to mention that now, after the cleanout, when I squeeze either of the intercooler hoses the pump note changes, which was not happening before. This I take to mean there is coolant flowing now.