no heat while idling and mysterious coolant leak

[97exploder19]

Got a little problem Id like to solve before winter comes. My 99 5.0 will have good heat while driving, but if the truck is sitting at idle, I have no heat or luke warm heat.

Also I noticed I have a coolant leak right under the engine. It only happens when I have the coolant reservoir filled. The reservoir and lines arent leaking. Any ideas what it could be?

Last year before winter I replaced all rad hoses, bypass hose, thermostat with an OEM one, and changed coolant. The temp gauge needle is always in the center of the gauge.

 

[Convict1997]

The are a lot of places it could be leaking from. I'd get a cooling system pressure tester. You should be able to rent one from one of the major auto parts chains. Pump it up and look for the leak. I'm guessing either heater core or the valve that controls flow of coolant to the heater core.

 

[bobflood]

Another common leak on the 5.0L engine is at the water pump or the timing chain cover. TC cover likes to leak in upper corners where the walls, and hence the gaskets, are pretty thin. Good luck.

 

[1998Exp]

Unless it's massive, a timing cover leak is mostly noticeable as a drip from the rear of the torque converter housing. Coolant is blown there along the lip of the oil pan. And, if the OP noticed it only when the overflow bottle (and hence the radiator) is full, perhaps it's a leak somewhere at the top of radiator. A leak there will blow steam with a hot engine and go unnoticed with a radiator that's not completely full, because when cold, the leaking spot may be below the top of the fluid - just a speculation...

As for the lack of heat at idle, it seems like an obstruction somewhere, perhaps it's as simple as the valve at the inlet to the heater core not fully opening. I believe that it can be easily removed and inspected.

Another common leak on the 5.0L engine is at the water pump or the timing chain cover. TC cover likes to leak in upper corners where the walls, and hence the gaskets, are pretty thin. Good luck.

 

[bobflood]

Unless it's massive, a timing cover leak is mostly noticeable as a drip from the rear of the torque converter housing.

Agreed - unfortunately, after dripping for a year or so - mine suddenly became "massive." At least it was easy to find then!!

 

[Turdle]

Lack of heat at idle is due to the low coolant level caused by the leak. Leaking more when full points to something up high such as the heater core, which will leak and send drips to the top of the passenger side primary catalytic converter where it evaporates quickly.

Refill coolant, run the heater on high floor and check inside the fenderwell, watch for a drip on the exhaust pipe. You might need to crawl underneath or remove the inner fender liner to see clearly.

If you see coolant ready to drip off the main pulley, it is surely a timing cover leak.