I have a 1990 jeep cherokee 4.0. It has a coolant leak only overnight.
I can drive for miles and miles and no leak, I can let it idle in my driveway forever and no coolant leak.
But if I let it set overnight it leaks coolant at the rear driver side of motor on the exhaust. I am stumped WTH.

 

well going off what you said it obviously dosent happen when its hot. look for a hose down there and try to tighten or replace it. sounds like when it cools down ( being so close to the exhaust it heats up quick) it opens up a small gap on where its connected.

 

Sound like hoses to the heater core.

 

I cant see any hoses on the intake side. Is the intake manifold on these liquid cooled?

I checked the heater hoses and core area, all looks well, And the leak is on the intake side at the back of motor.

 

Well get a flash light.. craw up under it.. look between header and block.. you will see some freeze plugs... im guessing one of them is leaking..

 

Freeze plug....I have a leaky one on the back of the block that does the same thing.

 

Dangit, not what I wanted to hear but I will live with it for now. Not that bad, and ty.

 

I had the same issue with a leaky freeze plug. It just so happens that this plug is located on the back of the head just inches from the firewall. I am pretty handy but wasn't ready to commit to pulling the engine or dropping the tranny. The leak was quite small but enough to cause me some problems with overheating. I was prepared to do a bit of cheating. I stumbled across a post about "water-weld" by JB Weld. It's an epoxy putty that dries rock hard in 1 hour. I cleaned the affected area very well and then cleaned it again. I used steel wool, emery cloth and throttle body cleaner on a clean rag. I was able to get a mirror back there to check it. It was good to go. I applied the "water-weld" and one hour later no leak. Drove it again today with no leaks. So far so good. I'll keep you all posted.