.008" is the absolute max. Even that is pushing it. You can have the seats cut into the heads further to sink the valves in, but then spacers need to be made for the valve springs to keep the proper tension...

If you have to go over .008", just plan on getting a new head.

 

I'm thinkin that I'll have to do my HGs. I've taken it to my "friendly for dealer" for a combustion gas test of the coolant fluid, it came back neg. no combustion gas in the coolant? still it pushes coolant out the cap... I then took it to another shop they do not do the HGs but can perform all other repairs on the 6.0 they too found no combustion gases in the coolant, Ive replaced my degas cap 3 times in the past two years because of this? my power is still awsome, no mods only an open element filter (for the reuseable filter) and a 4 inch turbo back exhaust. I've had my EGR valve replaced twice and my EGR cooler replaced once, and my EGR cooler hose replaced once. I have to check my fluids weekly, (which you should anyways) and about once a month I'm topping my degas tank off to about the MIN level. If I go any higher than that she really pukes the fluid out. I'm stumped. I can do the EGR delete but the HGs are beyond what I want to do on my own on this thing.

 

The coolant should only be at the "min" level at it's max. There is a TSB stating this. My dealer wrote on my reservoir with a permanent marker, and I've seen some that have an actual sticker put on. The "min" line is your actual cold max line. Take that into account.

I don't think you'd find combustion gasses in there anyways, once you shut the truck off all the pressure starts pushing back into the cylinders. I bet you still have blown headgaskets.

Sounds like the exact issues I was having for about a year, then this finally happened....

 

The second shop that I took it to did what he called a stress test on the cooling system? he said that he put it in a high idle for about 2hrs with the front of the radiator partialy block and got the coolant temp up to 220 deg. and still found not signs of gases? I hope it's the EGR because I plan to delete it very soon. also I would like to remove the cat or de-sooter what ever they call it now from under the truck so that I can better utilize my 4" exhaust. the EPA is killing these trucks and making enemys out of faithful brand followers. thanks Mdud707 for your advice

 

Yeah I haven't had a muffler or cat on my truck almost since the day I got it.