Head Gasket Problems on 87 GMC Safari

I believe I have a blown head gasket. I loose about 1 gallon of coolant every 100 miles. I keep filling it, but how long can that go on?

Anyway, is it possible to change the head gaskets in this vehicle without removing the engine?

Thanks With the amount of coolant that you are loosing you should look like a Orient Express going down the road.
You should have the system pressure checked for leaks. It may not be headgaskets and something else leaking. Also check the oil for coolant contamination and have a cylinder block test done to see if exhaust gases are in the coolant system.

You don't want to be driving around like that cause if coolant is getting into the oil then it will ruin the bearings. As for pulling the heads, yes you can take the heads off without yanking the engine out.