I thought I'd chime in on this one.
There is a "fix" for this problem, for those with some mechanical skills or a friend so inclined.
Disclaimer, I'm not a professional mechanic, just a knowledgeable amateur. I have rebuilt engines myself (they run fine), and I do all my own work on older cars (2004 or so).
I just bought a 2006 Civic from a friend (long, long time friend) - precisely because she learned about the cracked block issue and stopped trusting the car, after 130K miles and 13 years. I'm going in with eyes open.
First, a clear understanding of the problem. A crack sounds awful, even frightening. It impacts around 1% of the casts from 2006 through late 2008. Chances are most Civics won't have the problem.
If you have any R18 engine, though, you should approach the issue of driving this older car (any older car, really) with diligence and...well, not exactly suspicion but extremely watchful eyes. If that's not a style you can handle, you are probably going to find driving an older car disconcerting.
The crack in the civic always occurs in 1 (or 2, or all of) 4 places. It doesn't impact the geometry of the engine. Nothing is going to fall apart. Just about everyone who discovered a crack probably had it for weeks before they realized it. The issue is that it leaks coolant, and cooling an aluminum engine is absolutely paramount.
At first you'll see no symptom. The cooling system operates normally. The "trick" is the position of the water pump. It is around 1/3 to half way down from the very top of the cooling system (which is at the radiator cap). As long as the coolant is above the water pump, you won't notice any problem, but that is the problem. The moment the coolant drops below the level of the top of the water pump, it can't move fluid. By then, too, the water isn't filling the cylinder head (the top 1/3 of the engine, approximately). Moments, maybe a few minutes later, the engine overheats very rapidly, and is destroyed.
Honda replaced engines, probably as a public relations decision as much as a genuine repair. It sounds wonderful to get a new engine. They were replacing the R18 with a newer design that doesn't crack.
To ensure your engine lasts, you must watch. Every day, whether it is 10 miles or 50 miles, whenever the engine cools after being used, check the coolant level. Do this the way they tell you not to, thinking more like a mechanic than a consumer. Make certain the engine has cooled, then open the radiator cap. Look to see fluid is right at the top. It should be the same level every time you check. If it is, you're good. Add an ounce or two (keep some handy) so the fluid is flush with the lip of the opening, the re-apply the cap (so you don't put air into the system). Don't open the radiator when it's hot - the fluid is under some pressure, and is over 160 F.
The fluid should always be at the top. If it isn't, there is a problem. A new Civic is designed to run with the same fluid put in at manufacture for 100K miles. It is supposed to be a sealed system. This is why they tell you never to open the radiator cap. Now that is older, though, you must know if the fluid level is dropping. There's no meter or gauge. You can't tell by looking into the reserve bottle. You must look into the radiator, because now that it is older and you suspect a leak or crack could appear, you must check.
If the level drops, before you assume a leak, check the reserve bottle. The system is supposed to push fluid into the reserve bottle when heat expands the coolant (to avoid over-pressure). When the system cools, it creates a slight vacuum which draws fluid from the reserve bottle back into the cooling system. If you let the reserve bottle run dry that will draw air into the system. There should always be a little fluid in the reserve bottle on a cold engine, but not much.
Otherwise, you have to check for leaks (and, of course, that crack). I won't detail how one pressurizes a cooling system to check for leaks. You'll find such tutorials all over the web. Use that method to find where a leak is happening. It could be a hose, but check the 4 places known for the crack to see if you have it. Two are on the front, facing you as you stand in front of the car, and are known to be the most common places. The other two are on the side of the engine facing the cab and are much harder to see, but you have to check. Find the leak before driving the car.
If you find there is a crack, you can fix it as long as you've been diligent so that coolant was never lost to the point the engine overheated. If the engine overheated, the block is likely warped and there's no chance to repair that. This fix applies if you've been diligent, caught the crack early, kept fluid in the car, and once you know you have a crack you stopped driving the car.
There are videos detailing how to repair cracks. Many (maybe most) are genuinely real tutorials - some are, like me, from amateurs (or even less) who may not have genuine expertise, but learned of this like you are now reading here.
To repair the crack (and according to the various online videos for any engine/crack), remove whatever components are in the way (likely the exhaust manifold, some wires and/or hoses - depending on the location, maybe even the intake manifold for those on the rear).
Use a Dremel (or similar rotary tool) with a grinding tool (I've used the green stone tool with good results). Some only "clean" the area, but I follow the wisdom of "digging a canal" into the crack. I like about 1/8th inch or more, digging a "trench" over where the crack appeared. At the ends of the crack, I carve out a margin of material beyond the crack, and dig in a little deeper. These "ends" of the canal stop the crack from spreading (when it is sealed). I've gone so far as to dig all the way into the water jacket, but that's not required. Some only bother with the surface, just roughing it up, but you are going to seal this crack, and the idea of digging a canal is in line with similar repairs on cracks in cylinder heads.
Some mechanics will weld in new aluminum with brazing rods. If you're a welder, have at it. It isn't required, but that's a fine, well tested way of sealing such a crack.
I don't, and it isn't necessary. I use a "cold weld" approach, using JB Weld or any number of similar products. These are "epoxy" compounds with metal particles. They bond so well that it is actually stronger than the block's metal. A version of this "epoxy" is used to "glue" wings to aircraft. The bond is so strong the metal will break before the JB Weld does. It works to about 500 F or higher, but your engine should never get above 225 F (or it's ruined).
I uses the "standard" or "quick" version in the tube. There is a version (quick steel) that is like modeling clay, which I've used in other contexts, but the "standard" and "quick" versions are like a thick syrup, and can be painted in place with a cheap paint brush (the small ones, for kids - $1 for 8 of them). The brush is trash afterwards. You have about 5 minutes or so once the two compounds are mixed. I often need to use a second and third "coat" to fill in the canal, and I generously "paint" the compound all around the area to "latch" onto the block's surface.
That will seal the water jacket and stop the crack from expanding. If you get one crack, it is hard to say you won't have another in one of the other 3 locations, but the crack repaired in this fashion is not likely to be an issue ongoing.
Then, re-fill the system (watch tutorials - there's a technique to get out all the bubbles) with coolant, and drive on.
Keep watch. I'd guess you can only "let go" of such diligence if you found and repaired all 4 known crack locations on an R18 engine - but then, there are hoses and other seals that can let go, too - including the water pump itself. Never let coolant drop a couple of ounces without checking into why. That is the only warning you can have before overheating, though you might catch the scent of coolant dripping onto a hot engine if the wind doesn't carry it away before you notice.
I run this "new" 2006 Civic with green dye in the coolant. I'll see it on the block when I check daily.
Then, too, before I put this "new" (old) Civic on the road, I put in a new timing chain, water pump, all the hoses, the main belt, the spark plugs, the oil.....
