I have a major coolant leak, is not the water pump, appears to be leaking out driver's side of the engine rapidly. 2003 Grand Cherokee 4.0l . Runs fine; water in oil; any ideas?

 

Head gasket ?
Get a compression check done before anything else.

 

Has it been in the extreme cold? Was the antifreeze protection adequate?

 

Yes, and possibly no.

 

Runs fine, no loss of compression or there would be an engine miss. Something in the water jacket opened up on the driver's side of the engine. I was hoping someone would know what that might be on a 4.0. It's not from the rear so I don't think it's a rear freeze plug.

 

There are freeze plugs across the side of the 4.0... 5 if I recall.

 

I wonder if there is a block drain plug there that might have popped out...? I'm pretty sure that on 4.0 sixes there was at one time, I'm not sure about my 2003 Grand Cherokee...

 

Under the manifolds then?

 

There are core (freeze) plugs behind the exhaust manifold in the side of the block and a pipe plug drain just above the oil pan surface on the same side. What threw me was water in the oil. THAT could mean a cracked block.

A straight 6 engine is more susceptible to cracking because of the length of the water jacket acting on the metal, plus the long stroke adds to the area for the ice to work on. There is no support between the cylinder barrels and the outside of the block. On the passenger's side there are the cam bearing webs and oil gallery holding it together internally.

A lot of people who live where it's not usually freezing temps don't use a proper 50/50 mix of coolant because they don't think they'll need it. They don't realize that it cools better than straight water and protects the system from rust and corrosion as well. To me, it's the ultimate sin to destroy a perfectly good engine by HOPING it'll never freeze! Sad.

 

Yup gotta pull intake and exhaust manifold. If you have a block heater could be from that too.

 

Oh, yeah! I love block heaters! They fit in a core plug hole and will keep the engine coolant at 100*F all night when you plug them in. NOW would be a good time to install one if the block is okay. Kat's even makes heater wraps for batteries!

 

I have 2!! Not sure what the PO was thinking but yeah lol. Got a chuckle from that.

 

Heck, I've even seen an electric blanket thrown over an engine! IDK what good that did. In my younger years I tried a oil dipstick heater. Worthless! All it did was carbonize the oil on the stick! It warmed the oil but not the block.

 

There IS NO water in the oil.

 

Sorry, but I must have misread your original post.