Surfguygriff

Quick question. 2005 Bosxter S. I'm chasing a coolant leak and all things point to the trunk coolant filler cap. It's the older (996.106.447.01) version known to leak so I figured it's time to replace it with the newer (996.106.447.04) version. That said, various parts sites (Pelican, FCP, etc...) have conflicting references on the caps. Some show that the pressure relief cap should be in the engine compartment while the trunk filler is the simple non-relief sealed cap (987.106.044.00), and some show the opposite (vented in the trunk).

My question is which is correct?

quickboxster

The relief cap / bleed valve is in the engine compartment directly on the expansion tank. The fill cap in the trunk is just a cap.

ClemCLone

I had a similar problem with my '05 with 114K miles.
I was getting a thin film of coolant, the underside of the hood, on top of the oil-water relief valve.
there happens to be a decal there and it was always wet.
I replaced the oil cap with the new version and it came back.
turns out, it was the pressure relief valve. I got a new parts set and that fixed it.

old man neri

From the parts diagrams
Cap in trunk:987 106 044 00
Cap in engine bay:996 106 447 04

Download the parts diagrams here

Surfguygriff

What is odd is that Suncoast lists the 996 106 447 04 as applicable to either the engine compartment or trunk depending on year for Boxsters:

https://www.suncoastparts.com/product/99610644704.html

So mine could be correct in the trunk

old man neri

Correct? Not in my opinion.
Will work fine without issue and doesn't matter in the long run? Probably yes.

Spyder_2011

Just a note that you can also just change the O-Ring on the trunk cap, it is available separately and resolves the seepage issues. Seems they need to be changed every few years to keep them sealed.

M. Essaie

On a related note: if you don't want trouble with your cap, don't open it. On mine I can't see anything through the sight gauge but a blur and I'm too old to trust the "low coolant" idiot light. So.... on a couple of occasions I've opened the cap to have a look down the neck and on each occasion the following drive produced a leak from the cap. The 0-rings get old and hard, and also there is a false floor that lines the bottom of the area surrounding the fuel/oil caps. That warps up from time to time and binds, preventing full downward movement of the radiator cap. It may take quite a bit of torque to defeat that bind.....