Cylinder head gaskets seal a lot of different passages from each other and from the combustion chamber. The symptoms will vary depending on where the leak is. Coolant leaking into the oil is probably the least common failure but it can be the most catastrophic. Antifreeze will melt the first layer of very soft metal on the crankshaft and connecting rod bearings. This is rarely a problem if you replace the head gasket and drain the oil and replace it right away. To let that antifreeze sit in the oil for a couple of weeks will damage the bearings. The metal will start to flake off and plug up the tiny, precise clearances making it harder to crank the engine fast enough for it to start. At that point you need a head gasket plus bearings, and you may be able to save the crankshaft. If you get the engine started and the bearings are already damaged, you will do a lot more harm in a few minutes by chewing up the journals on the crankshaft.
Antifreeze mixed in the oil makes it look like light brown mud, and it loses its lubricating properties. The level on the dip stick will go up too. If the oil level is normal and you're seeing a white-colored creamy substance on the bottom of the oil cap, and maybe even some clear water dripping from it, that is due to condensation. It is caused by excessive short-trip driving and is not as harmful to the engine bearings as antifreeze is. To clear that up, the engine needs a good 30-mile run at highway speeds after it's up to normal temperature, at least once a week.
Most commonly head gaskets leak between the cooling system and combustion chamber because that's where there's the most pressure. You may see air bubbles in the cooling system reservoir while the engine is running, but it's more common to see white smoke from the tail pipe. When the leak is bad enough, once the hot engine is stopped, coolant under pressure yet for a while gets pushed into the cylinder and fills it. Liquids do not compress so the piston can't move. That's called "hydro-lock". You won't be able to crank the engine until that spark plug is removed, then the coolant will be spit out through the spark plug hole. If it sits like that for a few weeks, the water in the coolant is going to rust the piston rings to the cylinder walls and make it still harder to crank the engine.
Before we continue, we should also clarify some terms to be sure we're talking about the same things. "It would turn over and sound like it would want to crank but never did."
"Crank" and "turn over" are the same thing. Did it or didn't it? Some people think to "turn over" means to turn the ignition switch. It does not. It means the starter is turning the engine. "Cranking" means exactly the same thing, as in a hundred years ago when the engine was cranked with a hand crank. Some people confuse "cranking" with "running". An engine will not run until it is cranked fast enough for it to start. If your engine is not cranking, we have to discuss troubleshooting the starter system.
As for the "mechanic-in-a-can" products, there are some chemicals that work very well for what they're intended for, but when it comes to forming a high-pressure seal where a stainless steel ring has corroded away, I am very skeptical. How does that chemical know where it needs to congregate, and why will it stop right at the leak and not get sucked into the combustion chamber just like the antifreeze does? If you pour it in as a liquid, how does it know where to turn into a leak-stopping solid at only the one place it's needed? If it is going to magically plug a leak somewhere else, how does it find that leak and not confuse all the other passages as leaks?
No mechanic would ever repair your car with these kinds of chemicals. That's not to say they might not work in some cases, and that would save them a lot of time doing a miserable job, but no one is going to risk their reputation. We know that even if a chemical stops a leak for a little while, it's going to start leaking again in the near future, and on which deserted country road will you be sitting on when that happens late at night? If those chemicals really worked as they're advertised, all shops would stock them and promote them. They would fix a real lot more cars. Your cost would be much lower AND the shops would make a much larger profit. There's a reason they don't try to cobble your car that way.
Saturday, January 11th, 2014 AT 6:20 PM