Leaking cylinder no overheating 995sfe

[R31]

I'm getting air bubbles in the overflow after flushing recently (new rad cap also). I drove about 1000kms and still had bubbles and a mechanic reckons he did all the tests but could give me no info other than cylinder 4 is leaking exhaust. It has never overheated afaik, no power loss after doing 40000 on it in total and it somehow still runs smooth. Should I get another opinion or could it be something other than a headgasket problem? 

[trentmeyer23]

I would start by getting the cooling system rebled.

Did he perform a cylinder leakdown test?

[R31]

12 hours ago, trentmeyer23 said:

I would start by getting the cooling system rebled.

Did he perform a cylinder leakdown test?

I believe so, my leads were all tangled afterwards. Ive done another 3000ks since then and it wont give up.

[trentmeyer23]

Take it to another mechanic and have them inspect/diagnose it.

[Jim.]

I suggest you confirm that a leak down test was done and ask for the results.

How about a quick CO or hydrocarbon check of the cooling system? Has that been done? It is quick and easy to do yourself or to get the mechanic to do it if it has not already been done.

Surely the cooling system would have self bled all air out after 3000 klms plus, wouldn't it?

[R31]

How would I do that myself for in the future? I've heard of tests that check for exhaust in coolant but no idea where to buy it. After 6000kms it still runs fine so I threw some sodium silicate through it a few days ago for the hell of it and the bubbles stopped in the overflow so a bit of good news.

[trentmeyer23]

You need a compressor and a leakdown test kit to do the testing yourself.