More of a query than a problem which I hope someone can shed a bit of light on.

Following rain, the radiator tank is getting covered in water. (water rather than antifreeze mixture).

At first I thought it was the cap, but I've replaced it already due to a faulty seal. As long as the weather stays dry, the tank is dry and the car isn't losing any anitfreeze mixture.

I'm assuming that it's something to do with the intercooler intake scoop whereby water is somehow making it's way onto the sound deadening material on the underside of the bonnet and running across and dripping on to the tank.
It seems to happen no matter what angle the car is - the common denominator is that when it rains, the tank gets wet.

Does this sound feasible?

Is this a common occurence - hence the drain hole in the top of the tank?

 

I found the sound deadening under my Impreza bonnet acted as a sponge for water and when full would drip onto the engine, problem was it also rusted all the bolts holding the scoop in place. After removal I couldnt see what difference it was making so I left it off

Thanks Jay762 - based on your experience I'll remove the sound deadening and see how it goes. I'll take a look at the scoop fixings at the same time....

.... But why would the tank still get wet when the car has stood still for several days before a rain storm?

 

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condensation?

Removed the intercooler scoop today. The car had stood for a couple of dry days. It rained this morning and before removing the scoop the expansion tank was wet.

With the scoop removed it was clear to see that the gasket on the base wasn't doing much and therefore letting water past the rim and into underside of the bonnet/sound deadening. The water then tracked to the lowest point above the radiator tank. I've also removed the sound deadening because it had begun to deteriorate.

I've temporarily replaced the scoop while I source something to replace the base gasket. Clear daylight can be seen at certain points around the base so no wonder it was leaking.

 

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Quick update to say that the water ingress problem is now resolved.

As suspected water was getting past the inter-cooler scoop and running around the sound deadening and on to the top of the expansion/filler tank.

Removed the scoop again, cleaned up the recess and fitted a bead of butyl bolt on panel sealer (the sort of stuff that gets used as a water shedder seal in doors).

As supplied, the bead was a bit too wide for the recess so just gently fed it around the circumference, stretching it slightly as I went.
Then refitted the scoop, pressed all around before tightening down again.

Couple of rain showers later and the engine is still dry.