Chevy 305 over heating - The head gaskets have VERY small water passages. Is this normal?

Question

After taking off the heads on my Chevy 305 I can't find a spot where the heads are blown. What does a blown head gasket look like?

I think the cause of the overheating might be the extremely small water passages. Each head gasket water passage is about 1/8 of an inch in diameter while the passages in the block and head are much larger. Can this be causing the over heating? Maybe someone put the wrong head gaskets on?

Answer 1

Usually when the head gaskets are blown you'll see the difference on the surface on the gasket were the water cross over thru the seal.  It goes from the water passage ways to the cylinders, or from cylinder to cylinder.

Was there any sign of water in any of the cylinders/ spark plugs?

Could be wrong head gaskets but more common mistakes are installing them backwards.  Been there done that.   I'm assuming that you have diagnose the cooling system properly and everything is working correctly, and that the engine has the correct ignition timing, and is not running too lean.

Did you work on the engine before it overheated or did it just began to overheat? Have you tried running it with out a thermostat? was water circulating through the radiator?  Did it overheat at idle no load or under load driving?

Have the heads check at a machine shop to be in the safe side and install new head gaskets make sure to install them correctly read the instructions first to identified any markings on the gaskets and any special instructions.   Good luck

Answer 2

The small holes are used to control the flow of coolant through the cooling system. The holes in the heads and cylinder block are bigger only to enable removal of the casting sand.

If the water passages were all large, you would only get circulation at the front of the engine. Water takes the easiest path. You also want to make sure the coolant spends roughly the same time everywhere in the engine equally, to promote heat transfer to the fluid and to keep all the parts as close to the same temperature as possible.