996T - Coolant level, expansion tank, that sort of stuff...

[996TT02]

Here goes.

Background. Replaced radiators 4500km ago.

After 3000km, coolant level had dropped to just below min, so topped up. Guessed that was pretty normal, air bubbles, whatever.

After a further 1500km, level again on min, but bang on.

First Q. Is the level supposed to be on min with a cold engine? If so, end of story.

If not...

Second Q. No obvious leaks. However, there is a "waterline" of pink around the expansion tank top-bottom halves join/seam. Well not really halves but just to get the picture. Could well be due to filling accidents in the past, though pretty sure I always rinsed out well in every aftermath. Seems a bit unlikely to be filler cap leaks, due to the location, such leaks are contained and drain out.

Dammit, the question has not yet made an appearance...

I have two theories, assuming that yes there is a "leak" of sorts.

1) A failure of the black cap that contains the bleed valve, leading to overflow that runs around the seam by capillary action, etc.
2) A failure of the expansion tank, if these fail at the seam.

So, which is it likely to be, which knowledge of the failure mode of the expansion tank would help in eliminating?

Thanks for any help guys keeping fingers crossed that it's not the tank, it's not particularly yellow but reads like it's a definite pig to replace.

[Homer J]

The first level drop you mention could have been due to the system not being fully bled after the new rads. The full procedure is a bit of a chore.

The second level drop, less so. Without any obvious leaks it is difficult to say. But your right to look at the caps. The blue filler cap is a known weak point, especially if your on the older cap. It was re-designed after 2002 / 3.

Check you've got the latest design first.

I'm not sure of exact symptoms for a split tank. But I'd guess you'd see the coolant loss on your garage floor if that had a fracture in it? It sounds more like your loosing coolant as a vapour, so small fitting leakage or cap as your guessing.

Have a good listen around the rads and engine while the engines hot and the coolant is under the most pressure.

[996TT02]

I all but eliminated the blue cap, as overflow here would be contained, "walled in" and flow down the proper drain. The red staining seems to go around the seam indicating either a leak from the black cap subsequently running around the seam, or from the seam itself, if this is where these tanks commonly fail from. (?)

Then again I do not know whether the level should be at min when the engine is cold.

Unfortunately I noticed this just before I travelled (not with car) so I can't check anything, not even the manual... if anyone can advise that would be great I could look into sorting out an expansion tank if needed.

[Homer J]

Level should be mid point I.e. Joint between top and bottom halves of tank when engine is cold.

Missed that out of first post.

[Rockster]

Original coolant tank cap leaked with my Turbo. I replaced it. New part, better cap, part number ends in 02 or 04. 03 is missing.

With my Boxster the cap was leaking and I replaced it. Some months (at least) later when I was checking out a suspected non-functioning radiator fan the coolant tank finally let go with a gush. The seam long the bottom let go.

Back to the Turbo just within the last couple of months the water pump exhibited leak sign. A build up of anti-freeze residue appeared under the pulley at the bottom of the pump. Hard to see as the pump is hidden by a metal shield or something.

Replace the cap. The cost is small.

If you want to test the tank and the rest of the system drive the car around with the A/C off until it is fully up to temperature. By this I mean the coolant gage needle has reached its usual position and has been there minutes. Really you want the thing fully warmed up.

At a good spot raise the RPMs to say 1500 and hold until the radiator fans come on. When they come on shut off the engine. The heat load in the engine will raise the coolant temperature and pressure and this will subject the system to quite a bit of pressure, with of course the system hot, which is when a lot of the items will have the least resistance to leaking or in the case of my Boxster and its coolant tank when I did this just gushing coolant out of a tank that had been leaking slightly for a long time.

Or if the tank has any anti-freeze residue build up underneath the odds are high the tank's seam is leaking and should be replaced.

If you want clean this with fresh water and remove all the build up. Be sure the cap is new and seated securely. Note the coolant level in the tank. Note it accurately. Do not rely on your memory. And be sure you do not mistake the stain line in the tank for coolant. Remove the cap -- with the engine off and dead cold -- and remove the screen and visually determine the level of the coolant in the tank.

Then drive the car normally but be sure you drive it enough to get the engine fully up to temperature. These engines run cool as the Turbo's cooling aerodynamics are superb so you have to drive around at a slow speed in a low gear. My Turbo gets the warmest when I'm negotiating a crowded parking lot or driving around with my Dad in the car looking at houses. Lots of time running in 1st gear with very little speed to push any air through the radiators.

Every morning before starting the car confirm the level is unchanged. If it goes down there's a leak. Probably the tank but it could be the water pump or radiators or any hose although in my experience they are long lasting. Another source of a leak is the hose fittings at the engine block. The fittings are epoxied in but can in some cases loosen and leak. Most often tracked cars develop leaks at these fittings but the occasional street car has been known to leak. If the fittings are leaking this is an engine out job to put right.