Saab 9-5 question

I have a Saab 9-5 aero V6. It was overheating a little last week, and straight away filled the coolent, and had the car towed to my go-to garage that specialize in Saab. They came back with the water pump was done and that caused the radiator to crack. OK, fine and they also recommended I replace the timing belt while in there as it had not been done. The car has 130,000 on it.
Fine, I paid $1800 for all the above repairs and labor.
As soon as my wife drive the car on the way home it starts to pour smoke out of the engine hood and leaking green fluid rapidly. We call to get it towed back to the shop.
They call back next day saying the Head Gasket has blown and that will be another $1500 on top.
I basically said no way, how do we know when the head gasket was blown and was it down to their negligence. They said it was blown at the time the water pump went and thats the way it goes. Surely the tests they should have done on the car should have shown some fault before we came in to drive away.

Question- What would you do?
How is at fault? And how much should all this cost?

Cheers for your time

It is likely that the first overheating incident caused the head gasket to blow, but this would be rather difficult to prove. As to an alternative explanation, it is also possible that the cylinder head became warped during the first overheating incident–but was asymptomatic–and that this warpage led to the head gasket blowing later.

If you have worked with this mechanic previously, I think that he should cut you a break on the new repair costs, simply because neither of you can prove his case.

Thanks my friend. I have been with this garage for a few years and have been many times with the 2 saab’s we own. The price break I thought at least would be the customer service we should all see.

I’m in agreement with VDCdriver about this but might add this.

Shops often have a different methodogy for doing things and while the details behind this shop’s line of thinking is unknown to me I can tell you what I would have done.

First step is run a compression test and check the spark plugs for coolant contamination. If the head gasket does not have a breach in it yet the test can give an indication of any piston ring damage. If it does have a breach then it will be obvious at the time of the test.
With a failed water pump or radiator any cooling system test or hydrocarbon test would be meaningless.

On a job like this, it’s also incumbent upon the shop to operate the car for a while (in my opinion anyway) and make double sure there are no problems before calling the customer and telling them to come and get it.

What I would be a bit nervous about at this point is the condition of the rest of the engine. Overheating can ruin piston rings and coolant diluted engine oil can wipe out an entire engine.
One would hate to spend 1500 on a head gasket only to find out that you’re left with a car that has a knocking engine or is burning oil at a high rate. This goes back to the compression test and whether or not the engine oil was contaminated. Hope that helps.