upper hose is collapsed

I have been dealing with some overheating issues lately and right when i think i have them nailed down this happens.I replaced the t-stat late last nite and today i went out to make sure everything is ok.i drilled 2 small holes opposite each other in the t-stat to help bleed the system of air.

I will run the engine at idle and it will come to 200-210 and the e-fan will come on for about 10 mins, shut off at around 180. All is well right?

After shutting it off and giving it time to cool off, i go out to give everything a once over, and i notice the upper hose is collapsed in about 3 spots.
If i take the surge tank cap off it releases the "vaccum" and the hose goes back to its normal shape.


Any ideas what is causing this? I will be putting the stroker in and converting to the 91
+ set up in the next month or so, but i need this fixed untill then.

89
auto
rad. is less than a year old
tstat is 2 days old
e-fan works
mech.fan works

To bleed air out of the older closed systems you normally do it thru the rear temp sender on the back of the head with the back of the engine as high as you can get it. Thats how you top off the system from all I have been told abou the closed ones. The hose collapsing is from air and not enough coolant. System gets hot, coolant expands, fills all the nooks and crannies then when it cools off it contracts. Because the system is closed it then collapses the weakest point, the upper hose as the lower hose should have a big spring in to prevent this from happening. I don't know if drilling TWO holes at 12 and 6 oclock would have any effect, I'll have to think about that for a while..

I read the post, new radiator but did you install new hoses? When you changed the radiator did you notice if the lower hose had the spring in it?

the upper hose should not collapse since it should be at a pressure compared to the lower hose. This is doubtful but hope you have the right water pump on there. With the serpentine belt you need a "reverse" rotation water pump. that "might" explaiin why the upper hose is sucking shut.

Yes, a guy CraigH did a write up on filling a XJ coolign system like we have, do a search. He suppested you park the vehicle with the nose down hill, then fill the tank while you have the temp sensor removed from the rear of the head. conintue to fill until coolant runs out the sensor hole, the install the sensor. Continue to fill until you bottle is half full, then start the engine and let it run top off.

frsno jeeper said:

After shutting it off and giving it time to cool off, i go out to give everything a once over, and i notice the upper hose is collapsed in about 3 spots.
If i take the surge tank cap off it releases the "vaccum" and the hose goes back to its normal shape.

Click to expand...

You've answered your own question. The pressure cap on the expansion bottle is faulty. The cap serves two functions.
It's rated at a certain pressure e.g. 16psi. If the pressure inside the cooling system rises to more than 16psi above atmospheric, the cap acts like a valve and opens to relieve the pressure by allowing air in the expansion bottle to escape. If the bottle is overfull with coolant, then coolant escapes instead. Now you know why you shouldn't fill it above the "full" mark.
When the engine cools down, the pressure inside the cooling system decreases and coolant is sucked back from the expansion bottle into the radiator provided that there's enough coolant inside the bottle, otherwise it'll be air that gets sucked back into the radiator. The space in the bottle that's vacated by the coolant (or air) should be filled by air that's allowed to enter via the pressure cap. If the cap is faulty, air cannot enter so a vacuum is created inside the cooling system and bottle. The bottle is rigid and cannot collapse, the lower radiator hose has a spring inside it so that doesn't collapse either, but the upper radiator hose is soft and doesn't have a spring inside it so that does collapse.
Replace the bottle pressure cap and you should be good to go.