Possible cracked block. How to diagnose?

[Boobonman]

I'll try and keep this as succinct as poss, car is a 1992 Eunos 1.6 bought with query HGF.
I removed the head and sent it for a pressure test / skim, water jackets looked really manky and furred up, maybe had radweld or something through it before?
Head replaced with new head gasket, new water pump, belts etc.
Starts straight up, idle adjusted, seems to run fine, no fluid leaks or anything.
Took for half hour test drive, no problem other than some steam from rad cap after switching off, I assume this is an air lock.
Next day go back out for another test run having topped rad up, runs fine but after approx half hr seems down on power,shortly after down to two cylinders and James Bond style smoke screen from exhaust. Limp to layby, switch off.
Seems to have consumed all the water in the rad.

What can I do next from a diagnosis point of view? I assume the engine block is cracked or I have badly messed up somewhere fitting the head gasket. If it was the latter though, surely it wouldn't have run so well after going back together?

Any help greatly relieved.

TL;DR - head gasket replaced 20 miles ago, seemed to cure, now have even worse HGF symptoms

[FordPrefect56]

Manky water jackets says no anti freeze in it for a long period of time. The alloy has corroded. May well have then popped a core plug or cracked the block one winter if the coolant froze. Not sure why it's worth throwing money at a car that old anyway.

[Boobonman]

Well, I want it as a cheap track/fun car. Is there any way of telling for sure the block is kaput before I buy another engine to fit?

[FordPrefect56]

Pressure test the cooling system. If it doesn't hold pressure then you can dig deeper. Could be all sorts of things at this stage until you know more.

[227bhp]

^^ What he says. Either get a garage to do it or buy a kit on Ebay as they aren't expensive.

[RR-B fixer]

Use a block tester. Best way to check for failed block or head...
http://www.ebay.co.uk/itm/Universal-block-tester-k...

[Boobonman]

Won't that just show exhaust gases in the coolant? If the head hasn't sealed properly then that would also leak gases across wouldn't it?

I've gone over everything in my mind and I think that I didn't do the head bolts up to spec when re-assembling. They were a bugger to crack off when we took it off and I think we placed too much faith in my friends ageing torque wrench to do them up again. With my recent practice I reckon I can have the head off again in a couple of hours, plan is to take head off, check for obvious damage and see what the gasket looks like, then re-assemble and do the head bolts up tighter, new coolant and fingers firmly crossed.

I'll try to keep you updated, many thanks for your suggestions.

[227bhp]

You always resort to taking something apart after you've done your best to find out what it is first. The reason being once it's apart nothing may be apparent and you can no longer test anything.

[PositronicRay]

I've bodged up a pressure tester before. I used an old foot pump with pressure gauge + some pipe onto a bleed pipe. Note some cars aren't supposed to be pressure tested cold.