Reply To: Exhausted!

[ChrisParticipant]

some thoughts – you probably know all this but here goes anyway…

Steam must be from water. It’s either coming from the coolant or from some other water source – see below.
If the water is coming from the coolant it’s either the head gasket, the bottom liner seal or a crack somewhere.
If it is intermittent I would think it is least likely to be the head gasket – and more likely to be a crack in the metal.
The only thing I know about the bottom liner seal is that they don’t like being disturbed – hence Dave’s recommendation. Do they fail otherwise? – I haven’t heard of it but that doesn’t mean much.

So – I would think about there being a crack somewhere – which I guess would most likely be a liner – would a crack in the head result in water getting into the combustion chamber? This would need something like a UV dye penetrant test. See – https://en.wikipedia.org/wiki/Fluorescent_penetrant_inspection. But you’ve had the head pressure tested so that sounds unlikely. So that leaves the liners.
There’s a kit you can get to test the coolant for CO2 content – based on the premise that, if coolant can get into the combustion chamber, then combustion gas by-products can get into the coolant. Given that the cooling system is not pressurised I would think this is a fair assumption. Here’s an example of such a kit – others are available.
http://media.wuerth.com/stmedia/shop/masterpages0000/std.lang.all/07234.pdf

Where else can the water be coming from? A silencer full of water might give a similar effect. You would only get steam when the exhaust is hot enough to start boiling it off quickly. Then you see the cloud of steam and you slow down and the exhaust cools off again. Why would a silencer become full of water? Condensation / rain? Don’t know really but it might be worth checking this is not the case before ripping things apart too much.
In a previous life I did some emissions work on diesel engine development – there was a problem with the vehicle’s exhaust giving off a cloud of steam after sitting idling for a while and then accelerating. This was because the engine produces water as a by-product of combustion and that water was condensing in the cool exhaust and forming a puddle somewhere. Then, when roaring away from the lights it would be boiled off. It was worse on cold days.
In which case your corroded spark plug threads could be a red herring. Or not.

Chris