I have a 97 cadillac seville sls with a northstar engine. It has been in the shop a few times over the past 4 months. It started overheating so I took it to the auto shop, (which was supposed to repair it, so I figured). I had the thermostat, water pump, radiator, oxygen sensors replaced, but none of this seemed to fix my problem. Now it is back in the shop with a blown head gasket (which I do feel could have been avoided had it been properly diagnosed) I am low on funds and can not afford to replace the engine or repair the blown gaskets at this time. I was browsing the internet and ran across many sealants that claim to fix this problem. I would like to know if they really work and if they do which ones would be the best for an inexpensive way to repair my vehicle, or any other suggestions. Thanks!!

97Caddy

I'd start looking for another mechanic. I can't see any possible reason for replacing oxygen sensors when your vehicle is overheating; that's absolutely ridiculous.

To be honest, the head gasket was probably blown to begin with; the Northstar motors constantly have this issue. I don't personally recommend using a sealant; you don't know the extent of damage to the gasket and the sealant may not even fix the problem, not to mention the potential damage that the sealant could cause if it plugs something else up.

We haven't enough information to say why the sensors were replaced. Other than overheatin, were there any other issues?

Without knowing the mileage and repair/maintainance history of this vehicle, I'm just going to say that the Northstar has a reputation for the cylinder head bolts pulling the threads out of the engine block.
Initially, the coolant loss is insignificant and the overheat diagnose doesn't lead immediately to blown head gaskets.
Eventually, perhaps two or three bolts are worked loose and now the seal between the block and head is really compromised.
Then is when you're told the engine needs torn down.
Had your mechanic been more familiar with this condition, he may have been able to caution you.