Stalling '91 Caprice Classic

It may not be a cracked/warped head or block. It may well be that your head gasket has rotted out.

This has happened to me a couple of times when I've used just water not coolant. Ford Cleveland V8's are notorious for it! What has happened is that you've fixed the obvious pressure leak, and now that pressure found somewhere else to go.

What you may find is that you have a coolant leak into the cylinder but not into an oil gallery. The reason it runs rough on start up is that the moisture in that cylinder is not allowing it to fire properly. It clears up after a short while and the pressure in the cylinder keeps the water at bay and possibly pressurises the cooling system.

To test is simple. With the engine cold, remove the spark plugs one by one and examine them for signs of corrosion (rust) or water droplets on the electrodes. Refit each of the plugs after inspection. If you do find water or corrosion, there's your sign.

2/ Remove the radiator cap (another reason to do this when the motor is cold), Note if there is any air pressure release. There's another sign. (a hot cooling system will have pressure normally)

3/ Top up cooling system, leave the radiator cap off. Start the motor, there may be some brief air bubbles present at the radiator filler neck but they should subside after a minute or so.

If you find an ongoing stream of bubbles coming out of the radiator filler neck after 5 minutes. You have a blown head gasket.

What to do?

To replace a head gasket is not rocket science however it has a reasonable degree of difficulty and is not recommended for first time shade tree mechanics without appropriate technical assistance. Also you will need to have the appropriate tools to do the job.

A good mechanical workshop, will take about 4 hours to do the job not including sending the head(s) away for checking/machining. Good Head machine shops will be busy so it may take a couple of days for them to do your head(s) and get them back to your workshop.

It's the incidentals that get you. Depending on what else is found when they pull the head(s) off. Usually you find there will be other cooling system issues like hoses and welsh plugs(freeze plugs) that will need to be replaced. Depending on the mileage of the motor and how kind you or the previous owner has been to it you might be better off replacing it with a crate motor. Than rebuilding it.

It all depends on what is the car worth, its' general condition, how much in love with it you are and your ability to afford the appropriate repair/replacement. If it's a $300 rust riddled clunker, then (even as sympathetic as I am to old iron) it would not be a candle worth lighting.

You didn't mention if you have had over heating problems prior to fixing the leak. If you have had over heating (boiled the motor dry) issues then you are looking at a total rebuild/replacement motor.

Having done a little research on this car, it has a Chevrolet cast iron small block motor. So its a parent bore block no liners, cast iron heads and block.

You really have to get these badly over heated to damage them. The OP could well get away with replacing the head gaskets if the gaskets have failed because they rotted. That said, if the gaskets have failed through overheating then its at least a top end overhaul including crack testing the heads. However to do the job properly,it involves pulling the motor out and rebuilding (freshening) the motor with machining, decking, line boring, re-honing the block. Fitting first oversize piston and rings, main, con-rod and cam bearings, a new cam and lifters. While your at it replace all the welsh(freeze) plugs, waterpump, and check that the oil pump is still serviceable. Like I mentioned in my first post its the incidentals that get you..

In the US the factory supplied warrantied plug n play crate motor is a cheap option, makes it a bit academic to rebuild your heat damaged motor.