Where's It Going (coolant)???

[Larryjb]

Just to add to my previous coolant leak:
It was about the same as yours in terms of how much I was losing. I removed the heads and took them to a machine shop to rebuild. They tested both to make sure they were disposing of the cracked one, but they both tested fine. It seems that the crack was so slight that it only leaked once torqued to the block.

 

[mattbta]

Because cracked heads are common, a quick and easy check involves removing the valve cover and pressurizing the cooling system. Then you can look for seeping coolant in the head.

Check post #31:

https://www.tahoeyukonforum.com/threads/latest-oil-change-oil-filters.99646/page-4

I did not have condensation in the oil cap, no milkshake in the oil. My oil did thicken and darken between oil changes. Since doing the heads, the oil is still almost clear by the time I change it now.

The signs were VERY subtle for me.

Larry was very helpful with my questions when I was going through replacing heads and then replacing a refurb that cracked, too. In my case, they were both 706 castings and cracked in the same spot but Larry's were 862, IIRC.

Pull the valve cover, look for milkshake. If none, then look for clean spots near the bolt holes. If none, clean the shit out of the heads/springs/oil ports and pressurize. Observe with your UV light. Mine was obvious within minutes but others have taken significant time to bubble up.

First two were from original to vehicle heads, next two are the refurb that had less than 500 miles on it with UV - note the bubbles and visible crack: (click for larger)

 

[iamdub]

To make a crack even more difficult to check, in addition to only showing when torqued down, the crack may not leak unless it's at operating temperature. If you change your oil regularly and use good oil and the underside of the valve cover still looks dark and gunky, you may have a cracked head.

 

[S33k3r]

Could it be a tiny leak into his heater system? Is it possible he is luid coolant from the water pump weep hole?

 

[iamdub]

Could it be a tiny leak into his heater system? Is it possible he is luid coolant from the water pump weep hole?

He said he didn't smell anything and it passed a visual inspection, including using dye. But, you do raise a valid point in questioning if these areas were checked. We don't know for sure if he could smell coolant in his heater system nor smell coolant steaming off of a hot engine.

 

[treehan77]

Probably either water pump is leaking and burning off and you just can’t tell. Mine I missed leaking for a while at those T connections on the firewall. Def check that too. Otherwise, as prev people said, maybe trouble internally

 

[91RS]

706 heads?

 

[exp500]

Wrap the plastic Tees or any suspect leak with TP. If it gets wet it falls apart and stains.

 

[isp5190]

2005 XL...adding 1/2" a week. Three garages + the Dealer all say: "I dunno"!
No symptoms like rough idle (could balance a nickel on it), loss of MPG (none - gets 22 on the road), smell outside-or-in (none).

Did the big 4 Tests multiple times at different garages: Visual look, Pressure test (always good), Dye Test (no visible leaks), Head Gasket test (fine).
Then why have I added 1/2" coolant weekly for the past year???

My brother had a 2004 with the same issue. GM had an issue with the material heads were cast with and would seep coolant through the porous material. GM has a tablet to put in the radiator. He put the tablet in and it took care of the problem. It would be worth a try.

 

[OR VietVet]

Yea, those tablets were standard operating procedure any time we did coolant work on specific GM engines, especially Cadillacs.