Can't find coolant leak
 

I've noticed recently a small wet spot of coolant under the truck after I've been stopped a while and I'll be darned if I can't find where it's coming from. I've crawled around underneath with a flashlight and I can see that it seems to be coming from the back of the engine, maybe the drivers side, but there's no way to actually see that area directly. There's just no room behind the engine to get a look and there's so much other stuff in the way...

Looking at the shop manual isn't helping. It doesn't show any coolant hoses in this area, and I can't even tell if there are freeze plugs that might be leaking. There isn't any coolant in the oil (than I can tell), and it isn't leaking very much. It's just enough to make the bell housing wet and leave a wet spot on the ground. FWIW, the truck has 102,000 miles and runs good.

Can anyone tell me where this coolant might be coming from? I'd hate to take this to a mechanic and give them permission to do exploratory surgery. They could make up anything they wanted and I wouldn't be able to tell if they're wrong or right.

Most auto supply stores will loan you a coolant pressure tester. It connects to the coolant system and you pump up the pressure with a small hand pump. The pressurized coolant will then seep out of any leak in the hoses or engine and you will be able to visually identify where the leak is coming from.

Check up top. It could be leaking from the intake area, running back and down. Using a small mirror will help to see the back of the motor.

If your smelling coolant in the cab, & the ground leak spot is back under the middle of the firewall, you could have a heater core leak thats dripping out the lower firewall AC condensate rubber drain tube

Might be helpful if we knew which engine you have.

Thanks for the suggestions.
I've checked the intake (as much as I can see) and didn't see the leak. The problem is visibility. Actually, I don't think that the 4.0 has any coolant going through that plastic intake manifold, anyway....

Unfortunately, the pressure tester won't help. I already know I have a leak. The problem is being able to see where it's coming from. If I could open a door in the firewall and peer thru from inside...

Pawpaw, I'm not smelling coolant in the cab. Having had bad heater cores in the past, I'm familiar with that smell. It would fog the windshield, too. But the heater is on the right and my leak seems to be on the left. I'll have to add the engine size to my sig (but it does say FX4).

Does anyone know if the 4.0 engine has freeze plugs? I couldn't find any reference to them in the shop manual. If not freeze plugs, do these engines leak from the head gasket? I jacked up the truck this morning and tried looking in from the drivers side wheel well. I could see that the split line between the head & block looked wet (:( ), but I can't rule out the possibility that it came from above. Although I don't know of any coolant lines above this area.

I don't have the OHC 4.0L, so I really can't speak to it with any first hand expierence, but I haven't heard of any perstant problems with the OHC engine after about 01, when they got the chain tensioner problem worked out, unlike problems we had with the pushrod 4.0L lower intake manafold & head gasket leaks.

The pressure will make the leak easier to spot.

Finally found the leak source. I took it to the dealer and they couldn't find it at first. So they removed the intake manifold to search under there and then they were able to see the leak at the back of the head, coming from a hole that is used to suspend a wiring harness support. Apparently, the hole had gotten drilled a bit too deep at the factory and broke into a cooling passage. Sealing the bolt was easy. Why it took eight years to start leaking is a mystery that will never be solved, but I'm glad that they didn't have to pull the head to find or fix the leak. :)

Good find, fix, & feedback. Give the Dealer an attaboy, for finding & fixing that one!!!!

Ditto to Pawpaw. Nice to have a close on a question. I still have a problem that I haven't solved so I can't close it. So thanks!