No, previously I had flushed the core. This time I pulled the lines off the core to flush them back the other way to flush out the t-stat housing. But...

That didn't work either. The res level was down a little and once again there's a 1/2 air gap in the top of the radiator. It blew hot air for half a minute and then cold again. And now cold all the time. So it must be leaking down to a level and staying at that level resulting in enough in the system to cool the engine but not enough to get circulated to the heater core.

So now where's the leak? There is nothing visible on the outside and nothing that I have found to show the heater core is leaking. If there's an internal engine leak, I'm thinking, it wouldn't leak down to a level, it would just keep leaking until all of the coolant was circulated through and out of the engine. So maybe the radiator or the heater core is leaking? I guess it would have to be something kind of higher in the system since it seems to level out to a certain point in the radiator.

 

have you tried replacing the radiator cap?

 

Yep, brand new cap, t-stat, and water pump.

 

here's what i would try next.

fill up overflow tank and replace lid. fill up radiator and replace cap. locate the longest hose around the tb and holding it up sort of high, fill it. do it slow and allow air to escape.

so now you've filled the system from both sides of the t-stat, including the heater core. see what happens next.

i agree that if coolant was leaking out on the ground, or into the cylinder, or into the oil, it would continue to leak down.

if this doesn't work, buy a "leak down tester" radiator cap. it has an air valve where you pressurize the system up to 15 or 20+ psi. leaks will whistle or spit water. i'll look for a link...

well, damn these things are expensive. be careful of this one, i'm not sure it fits all sizes.
http://qualitytoolsforless.com/Produ...ProductID=3632

this one has more adapters.
http://www.harborfreight.com/cpi/cta...emnumber=65053

 

Ok, here's the latest.
I bypassed the heater core and both hoses run nice and hot. After filling the system again with clean water and then running it, the res tank went low and there was again a 1" air gap in the top of the radiator. Last night I bypassed the throttle body. Today we'll see if it continues to drop. I suspect it will.
Now, with as much clean water that I've put in it, the rad and res should also be clear water. Unfortunately it is the color of apple juice. So it's getting contaminated somewhere. I have again checked the oil (clear and brown) and the tranny fluid (clear and pink/red). If it drops again I'll bypass the tranny cooler at the bottom of the radiator and see what happens.
What a pain in the **** this thing has been.
What would turn water in the cooling system the color of apple juice?

 

rust from the water jackets in the cast iron block.

 

A Nissan 2nd Generation Ram?

wut?

 

Today she took it in to get the radiator pressure tested at a local radiator shop. The guy looked at the coolant/water and smelled it. He didn't want to or feel he needed to test the radiator. He said it's a blown head gasket or cracked head. That's what I was thinking for a while but trying not to think it too much.
She called a couple places to get a round about quote for either and they are talking $1400 to $2000 and a week's worth of work. That's nuts. You literally look right down on this motor. It's not like half the motor is under the dash or you even have two heads to deal with.