A friend of mine's wife was driving home yesterday and her car started to overheat. She kept driving it until it died, after it got so hot it wouldn't go over 30 mph, floored. So, big, bad hot, melted the temperature sending unit off. So we find a stuck thermostat and replace it. Thermostat will not open, pull it out, now it runs cool, of course, but it's losing water. It's not going into the oil, I can't see or feel any water vapor out of the exhaust, no indication of it being pushed into the coolant. So where is it going? I ran out of time to pull plugs and look at them and see if it is indeed going into a cylinder. But like I said no indication that it's getting exhaust gas pushed into the coolant. It's loosing about a quart every 5 minutes. So, what do you guys think, I'm still leaning toward cracked head, but I just don't know for sure.

 

typical, you need to tell women that when it gets near "that little red line" stop driving..........the motor is toast, either head gasket but more likley a warped or cracked head.......tear it apart

 

I'd edit that, but it isn't my post. I've seen male-type people do that, too. "Well, it still seemed to be running O.K."

My guess is that you either crakced some iron or warped a casting badly enough to lose the head gasket seal. Either way, a pressure test of the cooling system and a cylinder leakage test of all holes should be informative.

There isn't much of a question whether the engine will have to come apart for some items to be replaced. The question is do you replace just the heads, or the woman, too. I guess it depends on how good the head really is...

 

:sillylol:

 

A novice question on this topic... I understand if the engine is iron about it cracking or warping heads but what would happen if you overheat an aluminum block/heads? Isn't that worse than overheating an iron setup?

 

It's not a hard-and-fast rule, but cast aluminum TENDS to warp more easily than an iron casting. Gray iron castings will crack under stress a little more easily, however.

This, of course, all depends on the alloy of the castings in question. Cast steel is very rigid, but also has a tendency to crack, whereas aluminum will tend to distort a lot before cracking. Gray iron is somewhere between - generally.

The casting process can affect this greatly, too. Centrifugally cast items tend to be more dense and stronger, while plain old sand castings are a little less dense. Surge-filled die castings are a bit more dense as well, and therefore a little stronger. For reference, all case, intake, and head castings that I'm aware of are poured sand castings, regardless of the material used. Transmission housings and clutch bells are usually die cast with the molten metal being surged into the molds under extreme pressure. This is why such a thin aluminum casting can take such force and abuse without distortion or failure.

Aand none of this changes the fact that I still want to know if the quality of the head is worth keeping it....

 

Thanks a lot, Vader .