94 - 4.0/V6 coolant leak?

[Jsteck]

Anyone able to give me some feedback on where this leak may be coming from? (see attached picture)

Initially found a leak and couldn't tell where it was coming from. Believed the thermostat was stuck and thus caused undue pressure causing a leak on lower coolant hose on water pump. Thought I saw some fluid coming out on top near water pump. Went to drain the radiator and maybe 4 cups of coolant came out. I just replaced the thermostat housing, filled the radiator and started the engine and this leak was revealed.

 

[alwaysFlOoReD]

Post a pic from farther back, this one is too close.

 

[backporch]

looks like your white part is the thermostat housing, silver cylinder to right is a/c compressor and battle ship grey is lower intake manifold and the stream is coming out from below that. Must be the lower intake manifold gasket where the head and block and intake meet.

I have never replaced but it always gets mention that extra rtv is needed there. May also be a first point of failure. others can probably verify that.

By the way... that is a 94 and the engine looks practically new to me.. where is the rust?

 

[Dirtman]

By the way... that is a 94 and the engine looks practically new to me.. where is the rust?

It's obviously had a thorough steam cleaning...

 

[RonD]

Yes, hard to see what part of the engine that is.

4.0l OHV engines have an aluminum intake and cast iron heads, and this can cause galvanic corrosion where coolant circulates between the two different metals.

Passenger side front and drivers side rear corners of the lower intake are where the aluminum and gasket could get eaten away, although any of the 4 corners could leak



Just FYI, radiator cap holds pressure in the system, thermostat is for temperature control, engine and radiator have the same pressure all the time.
The thermostat just prevents circulation thru the radiator until engine warms up enough to need extra cooling.

The pressure comes from the coolant heating up, like all liquids it expands in volume when heated, this expansion creates the pressure, the radiator cap holds the pressure to it's springs rating, say 14psi, then at 15psi cap will open and release some pressure(coolant) to flow to Overflow tank.
When engine/coolant cools down the coolant volumes shrinks, if any coolant was sent over to the overflow tank then pressure in the system will go to -1psi, this will pull open the smaller valve in rad cap and suck coolant from overflow tank back into the radiator, keeping it topped up all the time.
This transfer of coolant from radiator to Overflow tank is normal, and will happen each time you drive vehicle longer than 20 minutes or so, that's why there are COLD and WARM lines on the overflow tank