Went on a drive today and the darn thing overheated! I hear a air in the heater core as well. I guess I have a combustion leak. Could this prevent water from circulating through the radiator? I did a block test (chemical changes from blue to yellow if combustion gases are detected) last week and it came out OK. I don't trust the test anymore so i'll do it again. But my question remains: could a combustion gas leak into the cooling system prevent flow through the radiator even if all cooling systems are fine (t-stat, radiator, hoses, water pump).

Thanks in advance.

 

I was just under my 01 disco today...and I have to wonder, how are you checking the temperature of the radiator? it's entirely encased in the shroud!

 

First of all why do you want to feel the radiator? You only need to do so if you are checking for cold spots (blocked). The radiator has a cover on top that is held with four screw clips. Remove them and pull up the upper rad hose and the upper shroud comes right out. Then you have large opening into the front and rear of the radiator. I wouldn't recommend sticking your hand down there with the engine running.

 

I did another block testandit turned from blue to yellow so combustion gases are detected. So it's either a blown headgasket or a slipped sleeve. When the engine gets very hot (over 220F)a tapping soundeminates from the engine. Sounds like a lifter tapping but maybe it's a slipped sleeve. When temp goes below 212 the tapping goes away. Any thoughts what that is. Only makes noise when engine goes overheat, otherwise it is quiet/no tapping sound.

The radiator always stays cold even though T-stat, radiator and water pump are fine and system does not leak. Temperature climbs over 210 regularly, fan comes on but radiator always stays cold. So it appears that combustion gases can prevent water flow through the radiator, how bizarre. Never sawcombustion gas prevent flow through a radiator on other cars but I guess this cooling system is somewhat unique. As mentioned radiator, t-stat, water pump and hoses are all fine and no external leaks.

I am running Blue Devil head and block sealer (sodium slicate) and will see if it makes a difference by at least temporarily sealing the crack, preventing combustion gases from going into the cooling system and finally check if the radiator gets hot as it should during heavy driving.

Update, the Blue devil didn't fix it. Will try one more time.[/align]

 

that's a bummer. I wonder how they go about testing for a slipped sleeve, other than the obvious approach of tearing down the block or dropping the oil pan.

I'm not sure if I mentioned it before, but your issue sounded alot like a problem that I still have on an 89 chevy pickup. Truck would overheat without warning. Replaced the T-stat, waterpump and even put an oversized radiator in. Flushed the entire system and she still overheats. Did the test with the turkey baster and it came back ok.

The strange thing was...if she started to overheat and I pulled over to check the upper hose, it was hot as hell but I couldn't feel any coolant. I've got one of those pressure release caps on the radiator, if I would pull over and very cautiously lift up on the pressure release, it would suck water past the thermostat and it wouldn't overheat anymore.