1. It's plastic.
2. You can see exactly why it dumps coolant when overfilled (the joint at the filler neck AND there is an open breather hole behind the base of the neck).
3. As speculated by others before, it blocks the flow of air through the oil cooler. Look very closely at the pattern on the oil cooler fins and placement of the OEM expansion tank.

In short, trash this thing and use a metal tank from Summit.

 

I too don't like its location, it is a pain to NOT overfill as you have to add a little, check the level with the dipstick, add more, etc.

Being plastic ain't such a bad deal....ALL expansion tanks I have seen are this same sort of white plastic that seems to be very durable.

As for blocking the airflow, yeah that is obviously a problem. I THINK that since the oil cooler air path exits thru the extractor vents behind the front wheels one may pick up a bit of a venturi effect at speed, meaning the slipstream of the car will help pull air thru the extractor vents via the ducting to them.

But yeah, seems like that particular item could have been better engineered overall. Not sure where else they could have put it...that engine bay is pretty busy!

 

Clayne,

can you post a pic of the summit one...

I guess it is smaller? I have easy access to it right now so it would be easy to change.

 

what is that at the top of the pic, it looks like a peice of wood.

 

It's a piece of tape, is my guess....from the wiring, you know.

 

ah, i see now. the light made it look like a peice of wood...

 

I will agree with all the facts, but I don't think it is that significant, the position of the expansion tank where it is right now. It would be different, if it was flush against the oil cooler.
At least until someone removes it and measures the changes in temps. A before and after temps, with same day temps and humidity, same driving style and time of recovery after heat soaked.
I still think, it won't do much or anything at all.

Bajaman, I agee with the venturi effect more than the blocking effect.

SNracing, believe it or not, it is a piece of toasted and faded paper label or paper tape. You would know this, if you have been working in that area.
Mine looks just exactly the same.

Clayne, pictures please. Is that still the stock IC???

 

That open gap where the filler tube enters is also why you get dirt in the coolant (road dust). It can be sealed with a rubber grommet (home made) or tape.

It's also why I use a small hose fitted to my garden hose and immersed in the tank to clean it out when I change the coolant. The small hose doubles as a siphon once the tank holds just clean water. Siphon it empty, then fill with coolant/distailled water. Removing the tank is a pain.

 

The other thing that I heard sucks is the line going into the overflow tank. It is like a few hoses stuck together with a plastic centerpiece in the middle.