2000 grand Cherokee 4.0 overheating. Got the truck with what I believed to be a cracked head or bad head gasket. Confirmed by dealership. Low compression on cylinder 3 and 4. 125 psi vs. 170 for others. So took the head off, didn't see anything. Down to machine shop, shop says hard to believe but it's fine. Put everything back together today and same problem. I can see compression through radiator fill. So now I'm thinking cracked block? No oil in water, or water in oil. Did have a coolant loss when I got it. All same symptoms as before I took it apart. Does the board have any input on this?

 

It is possibly a cracked block. You don't necessarily have to have coolant in the oil, or vice versa. It could be a crack between the cylinder wall and the water jacket. Sorry to confirm the bad news.

 

Well pretty much confirmed the cracked block. even took the T-stat out to see if there was a change. Funny thing is as hot as it gets, no heat. Both hoses do get hot though. So might be blend door. Pricing out motors now. We'll see

 

Ok i'm handing in my tools. On a whim I decided to pull the water pump. Previous owner said it was replaced and it looks fairly new. So, pull it and the dam impeller is broken in three places. Win for me! Can't believe I almost decided to go ahead and put a motor in it.

 

Man that's a big load off your shoulders. I'm happy for you

 

Thanks man. Now to finish cleaning and put it up for sale.

 

doesnt explain the low compression on two cyl thow

 

wouldn't a piston or ring be a more likely culprit than a cracked block?