I've been trying to hypothesize this for about week now. So to start off, I had a head gasket job back in Jan/Feb and I have not overheated/lost coolant since before that work was done.

The truck runs really smooth. I recently returned from Australia where I was away from the truck for a month. It was not driven in that time. I have driven the truck since I've come home with no issues. However when I checked the coolant reservoir after driving one day it looked practically empty. When I slowly loosened the cap, coolant slowly returned into the reservoir(though not all the way to the top).

I decided to add a little bit of coolant and I have checked it every other day since and it has maintained the level that I filled it. So I was wondering if this sounds like I've got a leak some where? Perhaps air in the system, or maybe there wasn't enough coolant added after the head gasket job?

It has been very very hot here for the summer. It is possible for some evaporation?

I'm getting ready to check all of the clamps. FYI I have seen no obvious leaking or puddles under the truck.

 

Bleed the system. Find Spikes post on how to do it, I think it's a sticky. Not difficult from the looks of it.

If that does not work, Find a coolant pressure testing kit, hook it up to the reservoir cap, fill it with pressure and look for a leak. I found a good kit on Amazon, but someone also posted saying that found one for 60 bucks at Harbor Freight that came with 15 adapters (one of which fits our reservoir cap).

Reads like you just have air in the system though.

 

Better yet do it my way. Only open, check or add coolant when the engine is stone cold, bleed it if necessary only with the engine off and make sure you keep your level all the way to the cap, check it a couple mornings in a row, if it continues to drop, have a pressure test done and get back with the results.

 

Question: I have flushed my coolant every two years (twice in the last year as I replaced ALL hoses and plastic lines a few weekends ago) and my coolant ALWAYS is just a fraction below the "fill cold" line, never dropping. Over the past few years, I have filled the coolant to the cap, when the engine is stone cold, only to check it the following day, to find it just below the "fill cold" line.

My theory is that as it heats up, under presure, the excess coolant escapes from the overflow tube, bringing it back to the same level.

I have NEVER had it go below that mark, and have NEVER had to add any coolant, except to raise it to the top of the reservoir, only to find it back to the original level the following day.

I don't think there is anything wrong with my cooling system, or am I missing something?

 

Systems tend to seek their own level, I have found just under 1/2 can stay at the cap level, the rest drop to a sweet spot and stay there.
Have you switched away from Dexcool, if not you should, also replacing your t/stat and cap if it is warn on the inside. Install one of the better coolants like Peak as well as a bottle of either Water Wetter or Purple Ice to help the engine run cooler.

 

That is correct. You can watch it happen/catch it out of the overflow if you care to.

My current Disco's coolant level likes to sit exactly where yours does, as do the two others I regularly work on. I wouldn't be concerned.

 

Mine sits there as well.

 

Just my $0.02 about my positive mystery coolant FIX. I HAVE NO AFFILIATION WITH AC DELCO and this is not an infomercial

I had a mysterious coolant "leak" for several months. I was probably buying a gallon of Dex (no peanut gallery comments please) every couple months to keep it topped off. Never overheated, no drip spots, no white smoke, no waterfall sound, etc, etc,...but coolant kept disappearing.

Pressure tested the system above the recommended pressure WITH my mechanic and we could not locate any leaks. He recommended I try some of the AC Delco Cooling System Seal Tabs that GM used/uses as part of their regular cooling system maintenance. I was skeptical, but I added 3 of these tabs per the instructions to give it a shot. For the first time in over a year, my coolant level has held steady, it has been full for a month and I couldn't be happier.

Not saying these things are a magic bullet, but they worked for the type of "leak" that I was experiencing.
2011-06-16_15-48-02_979.jpg?t=1308265324

 

That's great if it worked for you, but that is not a fix. It is a band aid.

 

Beg to differ, but I understand the skepticism.

I saw the TSB online for these things from GM, they are meant to help with the porous aluminum blocks (especially in Cadillacs) so in that regard I would say it is more like "stitches" to hold together a system that was flawed out of the gate. I had NO leaks show up on my pressure test, yet I was losing coolant, added the tabs, and I'm no longer losing coolant.....and I'm at 131K on the original HG.

I'll repeat myself in saying this product is NOT advertised as a "leak stop" nor should it be expected to repair any major issues. They don't stick it up on the shelf next to the garbage like "Head Gasket Repair in a Bottle" so I have more faith in it than I would anything you find on the shelf with bright shiny packaging.