|
The cylinder head gasket is a gasket (imagine that) that fits between the cylinder head (the engine part just below the valve cover) and the main engine block. It serves as a seal, or mating surface if you will, between the head (usually made of aluminum) and the engine block which is cast iron. As these two metals are different and expand at different rates as the engine heats up to normal temp, the CH gasket is crucial in maintaining the combustion cylinder integrity and sealing it tightly. The CH gasket has a hole for each cylinder plus holes for the water passages that allow antifreeze to circulate around the cylinders to cool them.
When a HG failure occurs, it usually “blows” between two adjacent cylinders or between a cylinder and a water passage. The latter situation can allow antifreeze/water to be sucked into the cylinder involved. If the leak is very tiny, you may not notice anything except an unexplained loss of coolant with no evidence of an external leak. A major failure is considerably more impressive (there is no doubt) with steam/antifreeze blowing out the exhaust, overheating and finally a no run situation. Compression from the involved cylinder can also be transmitted backwards through the rupture into the cooling system via the cooling passages blowing the radiator/hoses/water pump seals etc etc. The most common cause of failure is warpage of the CH itself, gasket materal failure or improper tightening of the cylinder head bolts which must be tightened in a specific sequence and to a specific torque..
Two worrisome questions arise when considering a car with a known HG problem. The term “external” HG failure implies that the failure has occurred to the outside of the engine which probably results in antifreeze and or compression being lost to the outside. The classic blown HG is usually an internal engine problem. Cars with HG problems often overheat if the driver doesn’t note the problem right away. If the car in question was driven hot for any length of time, the engine could have sustained major (often terminal) damage that might not be apparent right away. The other major problem is antifreeze contamination of the engine oil similar to what happened to your tranny. A large HG failure between a cylinder/water passage allows the piston to suck large quanties of antifreeze into the cylinder that in turn gets past the piston rings and ends up in the engine oil (not good). This antifreeze in the oil may or may not destroy the internal engine bearings surfaces. If it does, this constitutes a major engine overhaul.
HG repairs aren’t cheap ($1000. is probably close to reasonable) unless you know someone knowledgeable who can do it for you (still may not be cheap). It is SOP for the cylinder head to be taken to a machine shop after removal from the engine to have it “trued” or machined perfectly flat to remove any warpage. If the person doing the repair doesn’t plan to do this, take it somewhere else as it will just fail again. Sadly, there are a lot of jacklegs around looking for a fast $$$. If the job is done properly, it should be as good as new and last indefinately provided the above mentioned problems (overheating didn't occur and no antifreeze in the oil) didn't occur.
|
