Mystery coolant leak

[IIBRONCOS]

I have been getting a small coolant puddle only when the system is under pressure. I've used an inspection mirror around the heads, intake, all core plugs, and it all looks dry. The closest I can come to seeing where it originates is the rear corner of the drivers side oil pan has a visible drip on it, right next to the starter. It then travels down and drips off the bell housing. I don't see any sign of coolant higher up than there.
Anyone ever have a leak like that ?

 

[RonD]

Mystery leaks can be hoses.
Pin hole leak only sprays when engine is warmed up, pressure is up.
And it is invisible to the eye.

So you look where the coolant is dripping but leak is not there, so check near by hoses.

You can rent a pressure test kit, pump up COLD engine pressure to 25psi and then feel around for a leak, much easier on cold engine

 

[Ianjay]

intake manifold?

I was using coolant. Replaced all the hoses. The scary part was that it was burning (white smoke) a little too. Head gaskets? Decided to try the intake manifold gasket before taking the heads off. Fixed the problem. It has been a few years now and so far so good.
Apart from the leak, is there any evidence of coolant in the oil? If there is, the oil will become brown and there will be foam in the oil cap.
Extreme cold may have an effect on leaks due to shrinkage that may not normally occur. I wish you good luck in your search.

 

[IIBRONCOS]

I followed RonD and pressure tested the cooling system with the engine cold today. It took about 5-10 minutes for the leak to make it to the ground. It puts out about 6-8 drops every half hour or so. I had my inspection light and mirror everywhere I could put it. I still see no evidence of a coolant trail. I may try removing the starter to get a better look. It leaks so little it makes you not want to spend a lot of time tearing things down. I see no evidence of coolant in the oil, and no detectable white smoke by eye or smell.
The temps were moderate here, 60's-70's.

 

[RonD]

Could be Core Plug(freeze plug) has rusted thru, but they are usually gravity leaks, leak all the time, don't need pressure.

Hoses expand slightly with pressure so can seal up when cold and leak when warm and have pressure.

You can get UV Dye and UV Flash Light.
It can be added to coolant, or oil, or pretty much any other fluid, it is inert so doesn't hurt anything.
Then drive it a few days and in garage with lights out or at night look for the trail

 

[IIBRONCOS]

I have neoprene adjustable core plugs, and I can see all 6 on the block, and they are dry. I put new heads on the 2.9 and had no leaks for the first 1000 miles. I think I can see the head sealing surface to the block most of the way around the head, but there may be an area my mirror won't work to see. If I use sealant what kind do you recommend ?

 

[RonD]

You can't seal a coolant leak from the outside, unless it is a hose and you put tape on it, lol.

If a gasket is leaking then you have to remove it and replace it to get a good seal.

If it is a head gasket then you can try re-torquing that head when it is cold, but longshot at best.

Pour in leak stoppers do work but temp fix at best, because the metal parts of a cooling system expand and contract when heated and cooled, so any liquid sealer will not hold as leak point changes sizes so constantly needs to be resealed.
And if your rad or heater core are older and have narrowing passages then particles in the liquid sealer can finish them off, lol, fully blocking the narrowed passages, won't hurt new rads or cores, particles are not that big, just older ones that would have failed eventually in any case.

 

[4x4junkie]

Mystery coolant leak
I had a recent leak on mine that almost fits your description exactly. (All core plugs and areas around the heads dry) It turned out to be the clamp on the heater hose I recently replaced at the t-stat housing was apparently insufficiently tightened. Coolant would very slowly leak past the fitting (about one drop every two minutes), flow down along the edge of the water pump, over to the lip along the edge of the oil pan, and finally dripping off at the bottom of the bellhousing. When I first saw it, I didn't expect to find the leak at the front of the engine, but there it was.

Something to check for anyway.

 

[IIBRONCOS]

I had hopes of going out to the B2 and tightening up a heater hose clamp and being done with this coolant leak. I carefully looked around each hose fitting and found no evidence (dry or wet) of leaking coolant. I snugged the clamps a little anyway. I did another cold pressure test and after a minute or 2 coolant slowly started leaking off the bell housing. I took my inspection mirror and looked everywhere I could reach and saw no coolant. I reached around with my hand and all came up dry. I may have to run it in to a shop and see if someone else can locate it. Any other last ditch efforts anyone can think of ?

 

[adsm08]

There are freeze plugs in the back of both heads.

That is probably your cuplrit.