5.4 L engine has developed a leak between the cylinder head and engine block. At first I could see it leaking and spraying under the intake manifold. I brand of sealer. Seamed to work for a few days, but them I determined that is had blocked my radiator. So I flushed the entire system. There is now flow and I have driven the truck and it has not run any hotter than normal. However I have been having to add water. Yesterday I discover that with the expansion bottle (pressurized my truck doesn't have a radiator cap) open that water pours from a spot I can't see on the lower passenger side of the truck and has trickle in the passenger head area. I topped the water off, put the cap back on and it stopped leaking. So I ask now what????

Do any of the head gasket repair actually work. Does anyone have any experiences with one in particular?

I am really trying to avoid replacing the engine in a 17 year old truck with almost 300,000 miles

 

It seems your still not sure where the leak is.
On the rear of the engine you have the heater hoses at the firewall.
They are plug on fitting to the heater stubs.
I just had to replace one hose on my 267,00 mile truck.
Through the block valley area there is a coolant line from the front to the rear.
it could be leaking in the valley area under the intake or outside the rear of the block.
You really don't know what the repair should be until you locate it.
Good luck.

 

I had the coolant line under the intake replaced last year. The heater core is bypassed so it can't be that line.

 

Also check the freeze plugs.