Trouble with coolant cap !!!

[BoxsterLL11]

Having almost completed the servicing on my 981 I thought I ought to check the coolant.
Never done it (tut tut) in 4 years of ownership as I assumed there would be a coolant low level alarm.
Anyway, in taking the cap off when the engine was cold the level indicator was fully down.
I put in a mix of Porsche coolant and de-ionised water in, about 750ml.
But little did I know that from the min-max is about a quarter of an egg cup.
So it ended up being over the max.
Driven it over the last few days and obviously the excess has been expelled out through the cap.
To re-check the level, I tried to remove the cap tonight.
Bloody impossible by hand, had to use some pump pliers.
Thinking it might be coolant residue on the threads, I have washed the cap and the bottle threads but it only goes on one turn before it gets ridiculously tight again.
Has anybody had the same issue?

 

[tjb]

I believe it is easy for them to be overtight, after our last service I found that the cap had been put on back to front in that the coolant sign on the cap was upside down, being a bit OCD I tried to take the cap off to replace it back the other way round but it just would not budge. Had to take it back to the garage and asked them to shift it and put it on the opposite way round, they had a bit of a wrestle with it and I believe had to use pliers to remove it. I understand they can be easily broken this way as well.

 

[BoxsterLL11]

I'm not sure that the cap can be over-tightened as when it reaches its correct position with the icon on the cap the facing the correct way, the cap hits a stop and cannot go any further.
And am sure it can't be put on so that the icon would finish upside down in the fitted position as this would mean the threads are a double start thread (and have checked mine and its a single start thread) so for the cap to finish in this position it would have to be over-tightened by half a turn which I don't think is possible, or half a turn shy of its correct position.

I have just googled it and checked on some other forums and it seems to be quite a common problem.
Some owners have had to buy new caps on a regular basis.
On one forum it stated that the red floating stick should NOT be used as a guide for the coolant level. It recommended that the best way to check coolant level is via the engine access hatch (so I presume that is the one above the engine so not a 2 minute job to get access) and it is the level in the coolant reservoir that is important though obviously not easily accessible to see.
It is this reservoir that has the coolant level sensor so again assume if the system is loosing enough coolant to empty this tank then the sensor will pick this up and illuminate the "check engine" warning light and an OBD diagnostic tool will then show this.
Someone else recommended using a dry teflon spray on the cap threads and this seemed to cure the problem.

 

[AndrewCS]

I had the same with my 981 Cayman S ... there was internal damage to the cap, not sure what as OPC replaced under extended warranty

I have always checked the level regularly (CR - CS - GT4), any level indicator of that `bobbin float type` has to be initially `lifted` to check that it is free

Whenever I check the level the float is most always at minimum as it `must` settle out to that of the main header tank ... see picture for interface connections

As you say, it only takes a few mills to top up

 

[BoxsterLL11]

Thanks Andrew.
Mine was fine when I first took it off, topped up and then refitted ok.
But when I took it off again to recheck the level it was tight to get off and tight to put back on so am sure its not damaged.
Hence my thought about dried residue of the coolant being on the threads.
Having washed it, it is still tight but easier than before.
Am going to try the dry teflon spray.

 

[AndrewCS]

... when I took it off again to recheck the level it was tight to get off and tight to put back on so am sure its not damaged

I had the same symptoms and did not see any damage ... but the senior technician did

 

[AlistairF]

My OPC changed the cap at first service FOC. Said it had been overtightened (?) It takes little effort to move now in either direction. There is a definite stop when tightening.

 

[BoxsterLL11]

Have today given the threads on the cap a couple coats of spray dry teflon lube and the cap flies on & off.
Unlike yesterday when as soon as it got tight putting it on, I needed pump pliers to get it off.