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Engine blocks set low in the chassis to reduce the center of gravity and provide better handling. The skirt area of the block is the lowest portion of the cooling system. Coolants contain solids in the form of corrosion inhibitors, water pump lubricants, and anti boil additives. Antifreeze does not wear out, per se unless diluted, it will retain its ability to resist freezing indefinitely, but the additives in it do wear out. These additives form the solids in your coolant that fall to the bottom of the cooling system, as a thin mud, where it will solidify over time to become quit hard. The engine blocks ability to cool is reduced as this accumulation increases. Other debris from block scale, poor water quality, and core sand contribute to this problem. Regular flushing will keep this accumulation to a minimum, but can not remove it all, only engine disassembly can do that. Many blocks will contain large amounts of core sand, that should have been removed at the foundry. Core sand will not allow circulation of the coolant leading to over heating.

If you are rebuilding an engine, please be aware, that hot tanking, which removes oil and grease quit well, will not get the water jacket free of crud. Another method for cleaning is to place the bare block on an engine stand, rotate it upside down, then using an air nozzle and a piece of welding rod or coat hanger to loosen the build up. You will be surprised how much debris is still in there.

Over boring is capable of causing over heating problems. Cylinders are precision cast for location, this means that the more precise the casting the less wall thickness is needed for the cylinders. The small blocks are a case in point, being capable of only .030 safe over boring with out sonic testing. At .030 over many blocks will have less than .100 wall thickness left in some areas. Consider this dimension to be suspect, as many block have lost wall thickness over the years to water jacket rusting. I do not mean that over boring can not go past .030 because I have built engines at .060 over, but without regard for verifying wall thickness, .030 should be the maximum.

The last item to discuss here about blocks is the core plugs. Core plugs are commonly refereed to as 'freeze plugs', this being a misnomer. They were designed into the block to allow the foundry to shake out the core sand used to mold the block, they do not allow an expansion release in case of freezing.

Core plugs are problematic, in most cases the one that leaks is usually behind an engine mount, steering, or suspension parts, making it difficult to service. These plugs should be replaced if at all possible as a set. The reason being all the plugs are the same age, they have seen the same rust, bad coolant, and exposed to the same weather conditions as the leaking one. Ideally, the best time to replace core plugs is when the engine is out of the car.

An 'Axiom' in cooling system repair is, "you are repairing the weakest part, that is why it is leaking, now the next weakest part will fail because you just plugged up the pressure relief for the entire system. If I have not explained this point fully let me illustrate. You are wanting to do the right thing for that old car you just purchased, you drain the coolant and refill with new, replace the radiator cap with a new one, and guess what. The water pump starts to leak. Replacing the water pump, the radiator leaks. Repairing the radiator, the heater core leaks. Finally if a hose does not burst, a core plug leaks. Got the idea? Why change only the core plug leaking because the others will go out in short order. These type failures can happen in any given order, depending on where the next weak link is. Ford used stamped steel core plugs that rust from both sides, the brass ones from the after market are a wise chose, as they do not rust. Beware of the rubber expansion type as they are OK for emergencies but replace them as soon as possible with metal ones. The ideal time to replace the core plugs is while the engine is out. It does not have to be a rebuild, but out of the car makes accessibility much better.

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The cylinder block and heads are the major parts of the cooling system, both add heat to the coolant from the combustion process. Much of this heat will be conducted away from critical areas such as, valve seats, cylinder walls, and combustion chambers. Excessive heat causes critical engine clearances to be lost. Valve guides can tighten and gaul, scoring both guide and valve stem. Piston skirt to cylinder wall clearance is normally about .002-.003 on our engines, it can easily close up and cause metal transfer to the cylinder wall at high temperatures.. This both wipes out piston ring sealing and oil control along with piston skirt dimensions.

Cylinder heads warp across their deck surfaces, and crack at valve seats, and combustion chamber areas. Blown head gaskets are the result of these extremes in temperatures, allowing coolant into the combustion camber or crankcase.

Exhaust valves will be exposed to the full combustion temperatures, which can exceed the melt point of the valve material. Coolant is circulated through the head around valve pockets, seats and guides pulling heat from the metal, cooling them to operating temperatures.

Temperatures in the block and cylinder heads should never exceed the cokeing or burn limits of the lubricating oil. When oil is super heated it not only loses its lubricating ability, can also carbonize, and become abrasive capable of cutting metal. Both the block and heads have a series of small holes into the water jacket, down both sides of their deck surfaces. These are vent or relief holes. The propose of the holes is two fold, to offer coolant a way to circulate when the thermostat is closed and to allow air or steam pockets formed in the uppermost part of the block a way to escape upward.

Exhaust ports are exposed to extreme heat that could cause metal failure, were it not the coolant flowing around them. Porting and cutting on intake and exhaust ports, should be done carefully in order not to remove excessive material. The number one reason for this is that as the port wall thickness is reduced to the point that combustion heat is conducted at a much higher rate into the coolant. There is always the danger of hitting water Remember about 75% of combustion heat will be expelled out the exhaust, 20% into the coolant, and 5% into the air as block and head radiation.

Aluminum heads have many advantages over the cast iron, I will only look at the ones that relate to cooling. Aluminum has a much higher conductivity rate than cast iron, enabling faster heat transfer to the coolant. All specifications being equal, an engine with aluminum heads can run a full point higher compression than the cast iron heads, using the same octane fuel without pre ignition. The combustion chambers are cooler with aluminum. Where is this heat going? Except for lose to the under hood heat, the coolant is being utilized even more so to carry heat away with aluminum heads. It is possible for an engine to run hotter with aluminum heads, if the radiator was marginal when used with the cast iron heads.

Aluminum has a much higher thermal expansion rate compared to cast iron. Gaskets made for aluminum heads on cast iron blocks must be slick enough to allow the head to slide back and forth to compensate for this growth difference. Without this feature the gasket would shear and leak. Over tightening head bolts can cut the gasket or over stretch the bolts past elastic, at which point they will not hold torque settings. The result is the same, leaking gaskets. This seems to be a very difficult engineering problem, as most of the head removal performed on modern cars is from gasket failure.

Even momentary over heating can cause gasket failure. Iron heads on iron blocks do much better because the expansion rate is the similar.

Pre ignition or faulty timing can burn the metal fire ring that seals around the cylinder, leading again to gasket failure. Lean fuel mixtures, superchargers, and nitrous oxide can produce cylinder pressures and temperatures that can not be contained with out gasket failures, as well as burnt pistons. Some precaution are required to prevent these things from occurring. These safeguards include, larger more efficient radiators, timing retards, and boost controls. . This should in no way prevent you from supercharging your engine, just be aware of the safeguards needed to do so. Supercharging, nitrous, and higher compression ratios all produce higher levels of heat. In some cases with high boost the temperature gage seems to clime right along with the tach.

I hope that by now you are seeing just how important the heads and block are to the well being of your cooling system, and will give them the attention and maintenance they require. The block and heads are the foundation of the engine and doubly so the foundation of a good cooling system.

Next time on Woodys Tech. Board, we will look closely at:

Intake manifolds

Carburetor heater plates

Passenger heaters

And how they take their place in the cooling system.

PART 3

Mike the Radiator Man