Crack in the Engine Block

Hello,
We have had our Town and Country into the same shop three times in the last month. The first time was a new Radiator, the second time it was overheating and they replaced a belt. 3 days after they replaced the belt, it started overheating again and we brought it in and they said there was a crack in the engine block. What would have caused this and why did it happen all of a sudden when they just fixed the fact that it overheated 3 days prior? I don't know alot about vehicles but am I right to assume that either it was already cracked and they missed it or they didn't fix the real problem and it continued to overheat and crack? Help please!!

My guess is they didn't fix the real problem which is a cracked block. Most of the time overheating a motor will blow the head gasket and not crack the block. If you ever ran water and not anti freeze in your cooling system and it was winter that's how your block got cracked.

They are also trying some sort of sealant to see if it will work and letting it sit for 24 hours. I hear that (if it does work) it is completely temporary (which they failed to tell us) and they are also not charging us to do this, which seems very strange to me.

We live in NC, so winters here are very warm, we were putting in water but it was in summer only. How long will a vehicle run with a cracked block before it starts to overheat?

The cracked blocked was likely caused by the overheating 3 days prior. It was just not realized until you put the car back on the road with cooling system serviced and working properly. Usually, overheating does not result in a cracked block, or head, but there are other factors to consider like how long was the car ran hot and the engine make and type. Some engines are simply more prone to crack when they overheat, and some are not, ask anyone who builds demolition cars, they look specifically for motors that have a reputation as die hard, will run a long time while getting very hot with minimal damage.

Not using antifreeze causes problems that a lot of folks don't realize. Not using antifreeze in the winter most of time does not result in direct damage from water freezing in the system, it causes your engine to overheat, and that is what cracks the block, not the freezing water as you might think. Your block has "freeze plugs" in it designed to pop out if water freezes and expands inside the block. They are simple and inexpensive to replace. What happens is water in the radiator hoses, or more exposed areas of the cooling system freeze, which in its self does no damage. But when you start the car, coolant cannot flow, in very short time, you end up with an overheating situation simply because water cannot flow through the radiator in its proper cooling loop. Low antifreeze levels can actually cause the water in the radiator to freeze while driving down the road. If it's cold enough outside, the engine may not need a lot of water flow while cruising at a low speed to keep it cool, so the thermostat shuts down water flow enough to allow that water in the radiator to freeze or become slushy and plug the radiator, then when the engine needs that water flow to cool down, such as going up a hill, or in stop and go traffic, or at high speed, suddenly no water can flow and the engine overheats quickly. If water does freeze inside the radiator, it will usually expand and "pop" the radiator apart at the seams, requiring a new radiator, but that is much better than cracking the block.

Antifreeze does a couple of other things as well that are very important. It contains rust inhibitors, and without a proper mix of antifreeze in your cooling system, rust can overtake and clog the system pretty quickly, leading to overheating. It also has lubricants to help prolong the seals and bearings in your water pump, and extend the life of your hoses. It raises the boiling temperature in the system, and that as well as properly functioning radiator cap reduces coolant evaporation over time.

As already described, it depends on just how big the crack is. If it is small enough, and depending on where the crack is, you can drive the car short distances and just carry water with you. If the crack is in such an area that water is getting into the crankcase and oiling system, you are pretty much done. Might as well start looking for a replacement engine now. Sealants may help for a while, but they are not a permanent fix. I drove a '72 Caprice classic with a cracked head for years (the Chevy 400 small block of the early 70's had a reputation for easily cracking the heads as I found out after only 1 minor overheating session) The leak was right in between the combustion chambers, so the small amount of water coming in was vaporized during the combustion process and went right out the tail pipe. It was small enough that I only needed about a gallon of water a week, and I did a lot of driving, 35 miles 1 way to work. I carried a couple extra gallons of antifreeze mix in the trunk. Cooling system "stop leak" products had little or no effect on this particular leak, and it was very small, but being that it was in the top of the combustion chamber, to fair it had a tremendous amount of stress placed on it. Finally got around to putting a rebuilt head on it after a couple years.

It will help if you can drive it with the leak to loosen the radiator cap, as this will prevent pressure from building and blowing water out the crack under pressure. It can mean the difference literally of driving minutes or days depending on the nature of the crack.