Head gasket? Crack?

[hillbilly deluxe]

I have a '96 6.5 TD Suburban. It has 213k on it. I have a Heath Diesel computer and it runs really good. It has been leaking coolant for about 6 months now. I need to put in about a half gallon of coolant a month. It just makes a little puddle each time I park it for a while. I thought it was just a lower hose and I would get after it eventually. But here's what I noticed:

The cooling system is always pressured up. I expect that when its's hot, but I can park it overnight and come out in the morning and still relieve a bunch of pressure from the cap.

If I bleed the pressure off the system through the cap when I park it at night it stays bled off when I check in the morning.

I can't see how thermal expansion explains any of this. Seems like it must be getting pressure from the combustion chamber.

I've never seen any indication of coolant in the oil which I change every 3k.

Thoughts from the more experienced 6.x owners?

 

[63chevyll]

Well i did have a 6.5 TD that never got coooant in the oil. Same systems as you. And occasionally smoke white. Cyl 7 had a blown head gasket. Prety common.

 

[campfire]

I have a '96 6.5 TD Suburban. It has 213k on it. I have a Heath Diesel computer and it runs really good. It has been leaking coolant for about 6 months now. I need to put in about a half gallon of coolant a month. It just makes a little puddle each time I park it for a while. I thought it was just a lower hose and I would get after it eventually. But here's what I noticed:

The cooling system is always pressured up. I expect that when its's hot, but I can park it overnight and come out in the morning and still relieve a bunch of pressure from the cap.

If I bleed the pressure off the system through the cap when I park it at night it stays bled off when I check in the morning.

I can't see how thermal expansion explains any of this. Seems like it must be getting pressure from the combustion chamber.

I've never seen any indication of coolant in the oil which I change every 3k.

Thoughts from the more experienced 6.x owners?

This does sound like my Dad's cracked 6.5 block. Oil was fine, cooling system was pressurized while running. In that case, we could hear a trail of bubbles flowing into the cooling system. And it regularly belched out a water/gas combination. Sounds like your truck is not as bad. But it does sound familiar.

If this is what's happening, you will have a buildup of gas in the cooling system, and it will bubble out of the relief valve eventually. In our case, it was after just a few seconds. Your leak may be much smaller. But it will actively accumulate while the engine is running. The leak into the water jacket could be located in the block, the head, or the gasket.

 

[hillbilly deluxe]

Yikes. That's what mine does. I turn it on and start driving and it sounds like bubbling coming through the heater core. When I shut it down now I always bleed off the pressure at the cap and it comes bubbling through each hose up the the cap.

I'm about to go trade this truck in. It's my daily driver and I don't have time to fix it or to be without a vehicle.