Coolant can only go three places.

1) Out the overflow tube that runs down next to the air box (or some other external leak).
2) Burned in the cylinder
3) Mixed with the oil.

3.5 gallons is almost the entire cooling system. You're not going to have a hard upper radiator hose if there is no coolant in there to pressurize, the gases would just escape from the reservoir cap. To me it sounds like the coolant is either getting pushed out, or burned. Double check your oil to make sure it's not mixing. Cracked heads are uncommon, but not unheard of.

How many miles are on the truck?

You can also buy an exhaust gas test kit to see if the exhaust gases are in the cooling system (almost certainly if you're losing coolant).

 

3.5 gallons... that's pretty serious. Looks like the previous owner didn't take care of the truck. Take the above advise and start there. When I bought my LLY , within the first few months I had to replace the water pump and radiator hoses because of leaks. Then it started pushing out the coolant tank.

 

Thanks for the advice! The truck has 217k miles however, previous owner had some aftermarket stuff done to it, so probably drove it hard. After filling it up I then checked the upper radiator hose after sitting overnight, there was still coolant in the overfill tank, it was not hard and I could hear coolant being pushed into the engine. Im thinking it could be being burned, but then again, there is no white smoke. I checked the overfill tube, and there is nothing. I take off the cap after the truck has been driving and warmed up, there is no release of pressure noise. Relieved that it doesn’t sound like a train which I read means it could be headgasket but also im turning the cap very slowly, so maybe it’s released little by little until the cap comes off. Like I said, the only leak I could find is under the transmission, and that is the fluid coming from the bellhousing, did research and it sounds like its just gonna be bolts inside the trans, but I rarely if ever see coolant. I have yet to check out the weep hole on the water pump, but I would imagine that it would leak onto the ground if that were to be the case

 

Forgot to add, I checked the oil, the dip stick was black, not gray. But I must ask, how black should that oil be? Is the gray very gray or a lighter shade of black?

 

Note: It is RARE for a Duramax to dump coolant in the crankcase-!! Diesels generally turn the oil black a lot faster than gas engines- normal. The coolant dye test does not work well on a Duramax.


Fill the coolant and drive it hard, do not open the reservoir cap-- park overnight and see if you still have pressure in the morning- This seems to be a good test for bad head gaskets. You could remove the glow plugs and inspect them-- think "Steam Clean" that may give you a clue-!!
Also check the lower coolant hose where it attaches to the waterpump- show signs of leaking-?? The waterpump generally leaks when driving-- not when sitting.

 

I did look at the lower radiator hose, It did look like it was leaking, but then after a while I checked it again, and there was nothing, bone dry. I am going to fill up the coolant and drive it hard rn, let it sit overnight and see what happens, If there is no pressure in the upper radiator hose, I will check the glow plugs and EGR Valve for the steam clean look. Im hoping that it is just something simple and not a head gasket or cracked head!

 

Two common spots for coolant leaks that people miss are water pumps and the yellow/white heater hose fitting on the firewall. The coolant leaks directly onto the downpipe and can burn off before you notice it. The fact your low coolant light came on after driving it ten mins could simply mean it burped the remaining air in the cooling system. check the heater hose fitting/downpipe for wetness or white/orange crustiness as well as check the water pump weep hole for the same thing.

 

Ok, So I put coolant into it, Drove it hard for 30 ish min, maybe like 10 miles or so, and the coolant already dipped below the visable level, I really am thinking its burning coolant bad... but then again, if it burns coolant that badly, I should definitely see white smoke, there is no white smoke at all, I looked around and saw what could be it, underneath the EGR valve, near the cooler, there is build up, but its wet, like always wet, it only seems to lose coolant when driving, lower hose is dry as can be, looking under the truck, everything looks dry with no signs of a leak or residue from coolant.
Could the coolant be leaking from the egr valve onto the valve cover and then burning up since its hot? I dont see any smoke tho, but that also makes sense. It does seem to burn more coolant the hotter the engine is!
Ill attach some pictures of what I found and also my transmission, as I am sure you guys could tell what it is, Im pretty sure its leaking from the bellhousing.

 

Another picture, sorry it posted when I was trying to select the picture

 

My friend just brought up a good point, There is 0 pressure escaping the overfill tank when opening when hot, he is saying that a hose could be broken that I cannot see.

 

In your pics, I only see a glimpse of the side of the cooler tube...not any leak residue.

 

Yeah, since I talked to my friend, It really could be the cross over tube that runs under the intake, if that is cut then there wouldn’t be any pressure in the system I believe

 

Hooks' favorite picture...

As long as your oil doesn't look like this

 

Hooks' favorite picture...

As long as your oil doesn't look like this <img src="http://www.duramaxforum.com/forum/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" />

View attachment 1025715

Oh dear, 😂 It definitely doesn’t look like that

 

My 12v project in the signature had a HG failure and made my oil look like gravy

I fixed it though

 

My 12v project in the signature had a HG failure and made my oil look like gravy

I fixed it though <img src="http://www.duramaxforum.com/forum/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" />

Yikes! Yeah I am really praying its not a head gasket. Altho, None of the head gasket symptoms are matching up, If I am burning coolant, It would have white smoke, it would just have too, I would also see bubbles in my coolant, but neither of those are shown on my truck, its just lossing coolant with what seems to be no trace left behind

 

Pressure test the system.

 

Great Idea, Never thought about it, but Im gonna do that first thing in the morning!

 

Another possibility, if you still have the EGR, the cooler could be bad and leaking straight into the exhaust. It would blow it out through the turbo in that case, instead of burning it so there'd be no white smoke.you can fashion some temporary gaskets out of soda can walls to stop egr flow to the exhaust and also the intake. Then do the drive test again and see if coolant is pooling inside the cooler.

 

I know w this being an older thread you have solved or sold... one thing nobody mentioned is checking an inconspicuous spot on overflow tank. When I purchased my 05 lly the head gaskets were bad, but previous touchhole drilled a small hole where it could not be seen and would let pressure escape along w minimal Dexcool! Generally these duramax engines w failing/ failed hg will blow out overflow tank tube. My situation, although rare, has been an issue for others as well. You purchase a truck w blown hg and don't realize for months...Always examine the overflow for small drill holes. If you find any just walk away as people that stoop this low will deny or play dumb, which of course makes you want to smack em even more!

 

Internally Leaking EGR cooler is downstream of the turbo.....leaking there would drop coolant into the manifold/Y bridge air flow. Small amounts would go unnoticed.

 

Well, I believe I found it, This morning I pressure tested the cooling system and it barely hit 10 pounds before puking the rest of the coolant in my tank out because of a leaky hose near the intake manifold. Still there is no white smoke, so I believe my head gasket is fine since my engine was staying cool the whole time!

 

My 2015 used to have a low coolant level all the time. Went threw 3 egr coolers. Now my 2017 just had that come on this morning for the 1 st time. Just had the exhaust filter replaced since it would not regen. The filter was completely clogged and truck would not run. Not sure since they just replaced it 4 days ago if that is why my coolant is low.