So I've been losing coolant slowly and am trying to figure out where it's going. With a 10k trailer on a 300 mile tow next week, I decided to give it a closer look.

Facts:

There is no white smoke at all and no puking from the degas.

I dove into it today and found what looks like white residue on the underside of the front of the engine. I wiped it down clean and will check it again in a few days.

A few months ago I replaced the oil cooler, EGR cooler (BPD), and added a coolant filter. My deltas have been about 7-9 consistently since then, so a leaking cooler should not be an issue.

I don't see any coolant residue on the top of the engine anywhere.

I decided to check for blown head gaskets:

I hooked up a pressure gauge (0-60 psi from a local pool store) to the degas today and went for a drive:

After cold start there was virtually no pressure. Slowly rose to 2psi as the engine warmed. After fully warmed up it leveled off at about 7psi. If I got on it, I couldn't get it higher than 8-9psi. Not sure how accurate this gauge is really.

I'm assuming those numbers are within acceptable range for an unloaded run, right?

Any other advice on tracking this down?

 

The readings sound good to me. Sounds like a leak somewhere - perhaps the radiator, a hose, or even the water pump?

 

Lets hope. I was dreading having to do the heads after all the work and preventative maint I've done to it. Would a leak check from a local shop pressurizing the system be worth it?

 

I think so. You could probably do it yourself also.

 

theres a few places that I know of leaking ,by the heater core the the vaccume heat control valve leaks out the top screw, down by the ficm lower corner where the hose wraps around on a bolt, heater core it self, degus crack hair line.

 

Let's play a game. It's called "Guess the coolant loss source on a 6.0".

Hmmmmmm. From what the OP describes, there are a couple places where coolant leaks come to mind. The water pump weep hole would be the most obvious source from the area in question. But given the OP has just recently replaced a set of coolers, secondary guesses would be a nicked o-ring on the metal tube going into the front cover on the passenger side of the engine, just below the alternator. And/or the fat rubber "donut" o-ring that seals the coolant passage between the intake manifold and the front cover. The latter two sources would be the more likely suspected sources, due to the need to remove them when doing an oil and EGR cooler replace.

All kidding aside, a pressure test will pinpoint the source of your external coolant leak with a far greater degree of certainty than my guesses behind a keyboard, miles away from you.