Hello all,
This is a Nissan truck, 4-cylinder, question, so I'll understand if nobody is interested in it.
Anyway, my truck would lose water without notice. It got hot (several times) and died (the last time). The oil was very milky. I kept check on it before that and it was always fine. I would check it twice a day trying to find out where the water was going. I must have been burning it. And looking through the oil fill, there was boiling water on top of the head, five minutes after it died.
I took the head off last night and unfortunately the head gasket looks good.
So, which is more likely, that I have a cracked aluminum head or a cracked iron block?

Thanks,
Danny

Hard to tell really but I've found the head will usually warp before the block will crack.
All depends on how hot is got...

Danny,
Some of the Nissan engines have a problem where the timing chain gets loose at high mileages and actually will cut a groove in the front cover into a water passage. This lets the water get into the crankcase and mix with the oil. If the engine has any kind of miles on it, you probably need to pull the timing cover and take a look.

My B-I-L's '67 Firebird 400 motor had an aluminum timing cover-w/p mount on the front of it that corroded and did the same thing Bill mentioned.

Boy, did he get MAD!! I think the front lip of the pan bolted to it so wasn't fun at all to get to...

pdq67