How do you tell if there is a head gasket leak or a cracked engine block?

Answer 1

Having lived through both events in different cars myself, the tell-tale signs vary depending on where the crack is, not just if it is block or head gasket. Sometimes when it happens it is horribly obvious, like smoke billowing out the tailpipe, while other times it is almost unnoticable. A tiny crack in the wrong place can be worse than a larger crack in other spots. Some folks think their block is cracked when they notice coolant leaking out. This can be from a crack in an engine casting plug or a bad radiator hose, which is relatively easy to fix compared with real crack issues as discussed below. A crack in the head gasket or block between the water jacket and cylinder causes coolant to exit through normal engine combustion, and/or blow-by to enter the coolant. Indications you have this include one or more of the following: the formation of a grey sludge on the PCV valve and oil filler cap (things that have exposure inside the valve covers); discoloration of the coolant; a whitish coating formed on the inside of the tailpipe or on the affected spark plug(s); loss of coolant over time; coolant being pushed out the overflow tank as the engine warms; overheating of the engine due to the loss of coolant; passenger compartment heater quits working caused by the large air bubble in the cooling system, smoke out the tailpipe (usually whitish or grey). A crack between an oil galley and cylinder usually causes horrific smoking out the tailpipe, and discoloration of the oil. A crack between oil gally and water jacket is less common, but has similar problems as a cylinder crack, but usually no smoking. Most of the time the head gasket is where the crack is, although it is possible in the head or block itself. Also, a "warped head" can do the same thing when the head becomes distorted due to excessive heat. The fixes depend on what is wrong, but in any case it won't be cheap. A cracked head gasket fix at a shop is likely to run over $500 if they do the job right, and probably more if they rebuild both heads. A cracked block and you are looking at more major costs, up to a new engine at $3000 or so. I have nursed some headgasket cracks along for quite a while using block sealer, but ultimately only a replacement will work. I also suspect that the block sealer plugs up other openings that may cause more trouble than it is worth.