Heater Hose Question

[Tryfan]

Which heater hose is the inlet into the heater core at the firewall and which one is the outlet. One of the hoses comes from the water pump and the other one comes from near the thermostat housing. 2001 XJ, 4.0 I6, AW4, A/C. Thanks

 

[CharlesS]

The one on the thermostat housing is the return and the one coming off the waterpump is the supply....
Usually which ever fitting is higher is the return and the lower is supply.

 

[Tryfan]

Thanks Charles

 

[O-Gauge Steamer]

The one on the thermostat housing is the return and the one coming off the waterpump is the supply....
Usually which ever fitting is higher is the return and the lower is supply.

Actually... Per my FSM, the coolant path is from the T-Stat housing to the heater core and it returns to the pump. The bottom line at the heater core should be the supply. The factory did this to aid burping... Just as the Transmission cooler in the radiator has the inlet on the bottom and the return to the trans on the top.

 

[hubs97xj]

The FSM shows the heater hoses crossing at the core, which is not how my Jeep is set up. Top (larger) hose runs from Tstat housing to heater core; bottom (smaller) hose runs from heater core to water pump. Top hose is supply.

 

[CharlesS]

Thanks for correcting my mistake.

Guess I should have looked at mine instead of going by memory... :eyes:

The hose leaving the thermostat housing supplying the bottom connection of the heater core is higher pressure than the one leaving the upper connection returning to the water pump....

 

[ehall]

plus the coolant in the thermostat housing is hot, which is useful for a "heater" core

 

[Tryfan]

Thanks to everyone for resolving this

 

[O-Gauge Steamer]

So, why two different diameter lines... The theory is relatively simple.

Feed side is the smaller 5/8" line and the return is the larger 11/16" line. Using a larger return than the supply creates a local pressure drop on the return side which promotes flow.

Leastways, that is how it was explained to me back in 1960... I guess physics still works. At my age, it is kind of difficult to tell. Considering how many other thing do not exactly work as designed.

 

[hubs97xj]

The hose from the thermostat to the heater core is the "hot" hose, and it's larger. The smaller hose is the return to the pump. Big hose on top, little hose on bottom. While it may be drawn that way in the book, the hoses do not actually cross each other.

Two sizes = no mix-ups on the assembly line.

 

[Tryfan]

Actually I just checked my hose routing and the larger hose is on top and runs from the thermostat housing to the firewall. The smaller hose is on the bottom and is actually attached to some hard line pipe that comes out of the water pump and then runs to the firewall. But I am still not 100% certain, which is the direction of flow into and out of the core.

 

[ehall]

The thermostat housing has the thermostat, but it also has a small bypass port for the heater core. This lets the thermostat stop coolant from moving out of the head and into the radiator, but still allows the (hot) coolant to pass to the heater (otherwise the heater would only work when the thermostat was open). Meanwhile the water pump draws coolant from the radiator and the heater core, and pushes it into the block. When the thermostat is open, the pump is able to draw larger amounts of coolant than when the thermostat is closed. However there is always some circulation since the bypass port in the thermostat housing is always open and never closes