Engine/Transmission (1994 - 1998) 98 12v no heat. What is hose attached to back & front of theromostat housing?

[TBartlett1]

I'm working on a 98 with no heat, coolant is full and radiator is warm indicating a stuck thermostat or other problem.

I noticed a bypass hose that goes from the back of the thermostat housing to the front of the housing. Never saw this before & it doesn't look right.

Attached is a photo.

 

[GAmes]

That little hose connects to the wobble valve. I'm pretty sure that is it's name. The valves function is to bleed air from the engine cooling system. It is the reason you shouldn't leave the rad cap off after servicing the system. As far as I know, all 12 valves have them.

 

[TBartlett1]

My thought is that this is partly responsible for the engine running cold.
yes no??

 

[Missouri Mule]

One way check valve (right from service manual). States they don't use jiggle valves any more. The one way check valve is supposed to vent air when the cooling system is being filled. It also blocks coolant flow during engine operation (all coolant will go thru thermostat). Water pressure of flow will hold check valve closed.

Could be bad check valve.

Have you checked tempature blend door/cable to blend door?

What is the temp guage reading?

 

[TBartlett1]

So it is a 1 way check valve, I will pull it to check operation and also the thermostat.
Didn't check the blend door.
The radiator was only warm as were the heater pipes indicating the thermostat was stuck open or the vent valve/thermostat was defective.
Thanks for thr info.
Gona get on it this am.

90cummins