56 plate Rav4 TX4 D-4D: coolant becoming pressurised

[midLjohn]

56 plate Rav4 TX4 D-4D: coolant becoming pressurised so that spurts out of cap release tube whilst car being driven.  Block test indicates combustion leak.  After a run and when engine totally cooled to ambient, coolant reservoir remains pressurised depressing coolant level until cap released.  No visible effect on coolant.  No visible effect on engine oil.  No loss of coolant whilst car not being driven.  No loss of performance.  If car driven so as to minimised load on engine, little if any spurting: delaying each transition to a higher gear: ending up 60 – 70 mph in fourth.  Advice so far ranges from cylinder head gasket replacement to complete engine rebuild around new cylinder head and  block – can’t remember if long or short.   

[IanML]

Well, there's a dilemma.  I would tend to the gasket change, but I'm an optimist.  Perhaps you should take the mileage into account, and only consider the complete rebuild if its really high?  What is the rebuild cost vs. trading it in for a younger model (maybe a hybrid)?

[Rosgoe]

Have you had a sniff test done on the coolant to see if there are exhaust gases in the coolant a decent garage will do this for you.

[midLjohn]

Thanks to IanML and Rosgoe ... Mileage 160k: Reckon rebuild cost cheaper than upgrade to what would be as good as my rebuilt car: prefer this model to the later Ravs: Will sniff test tell me something the block test hasn't? Cheers

[Rosgoe]

28 minutes ago, midLjohn said:

Thanks to IanML and Rosgoe ... Mileage 160k: Reckon rebuild cost cheaper than upgrade to what would be as good as my rebuilt car: prefer this model to the later Ravs: Will sniff test tell me something the block test hasn't? Cheers

Must admit I have never heard of a block test but if that threw up a combustion leak then you will almost certainly have combustion gases in the coolant pointing to the head gasket.

[midLjohn]

It's what garage called the test where they drew a sample of coolant and added an indicator colour change of which showed combustion gas contamination of coolant.  Some quite experienced car maintenance guys puzzled by combustion gases getting into the coolant without any visible effect on coolant or oil, but seems like this is not an issue for you in terms of diagnosis. 

[IanML]

47 minutes ago, midLjohn said:

I...  Some quite experienced car maintenance guys puzzled by combustion gases getting into the coolant without any visible effect on coolant or oil, ...

Well, there is a visible effect on the coolant - it is being displaced out of the system.  I don't think a whiff of exhaust gas changes the appearance of the coolant.

[midLjohn]

Granted, but they are puzzled by the fact that in their experience whenever there has been a head gasket failure there has been a mixing of oil and coolant with the obvious visible effect on the coolant and oil per se.  I'm taking from these responses that I can now counter them and tell them that gas leaking into the coolant can happen without oil and coolant cross-contamination.

[IanML]

That is my experience.  It all depends on the position of the defect in the gasket.  If it just "bridges" between a cylinder and a coolant passage, no oil gets into coolant, and vice-versa.

[midLjohn]

Thanks for this confirmation.  Much appreciated.