Weird Cooling System Problem?????????? [Archive] - : Jeep Wrangler JK Forum

: Weird Cooling System Problem??????????

11-12-2008, 03:06 PM
I took the Jeep over to friend's last night to enlist his help in wiring up a new set of lights and the CB (but mostly to use his heated shop :D). His place is about 15 miles away so the Jeep got fully up to temp before arriving. Once there, we opened the hood and started to work. Half an hour into the project, he says to me, "look at your upper radiator hose". In short, the upper hose had collapsed as though you blocked one end and put a shop vac on the other. Now both of us are lifelong gearheads but we had never seen anything like this. Released the radiator cap and the hose resumed its normal shape. Then twenty minutes later, as the Jeep continues to cool, it does it again. This was repeated several times during the three and half hours we worked on the Jeep. Anybody have any ideas why? OBTW.........coolant level appears to be correct and the idiot guage never moves from its normal position when driving. :confused:

11-12-2008, 06:10 PM
any coolant in the overflow?

It sounds low and is creating vacuum

11-12-2008, 10:36 PM
Like paragon said. Check your Fluid level. I've had the hoses do the same thing on other vehicles.

11-13-2008, 06:41 AM
That's the weird part. Both the radiator and the coolant overflow are at the correct levels.

11-13-2008, 09:31 AM
When the thermostat is closed the water pump can create a little vacuum in the radiator, but this is a normal operating condition and your hose shouldn't collapse. If the levels are all correct, you could have a bad thermostat.

11-13-2008, 02:28 PM
Before I replace the t'stat, any chance this could be a problem with the radiator cap or the recovery tank hose?

11-13-2008, 02:33 PM
I would check the hose to the overflow to make sure it isn't pinched off somehow and if it's OK just replace the rad cap.

I could see something pinching the overflow hose and allowing the built up pressure to release into the overflow, but upon cooling down, if the little hose is pinched any, the vacuum would make it collapse and seal more... then causing vacuum in the rad itself which would make the upper hose collapse.

I'm guessing a rad cap could do the same thing.

12-28-2008, 12:17 PM
I agree with the hose to the overflow or the radiator cap being the problem.
With the coolant pump not pumping (engine off) these are the 2 likely to cause this aside from very rare exceptions. The thermostat wouldn't cause this, even if it is completely shut and doesn't have a bleed valve the pressure could still equalize through the radiator and the rest of the system.
As the coolant cools it shrinks and needs to pull coolant from the overflow to take its place. If there is not coolant in the reservoir it should still pull air, which is not good but the hose still shouldn't collapse. The components involved are the radiator cap, overflow and hose.
Radiator cap - most commonly has a seal at the top, a sealing surface held by a spring to set the pressure (also allows expanded coolant to reach the overflow) and at the bottom center of that it has a little one way valve. This one way valve is what allows coolant to return from the overflow jug, if this is stuck it could lead to the radiator hose collapsing.
Hose to the overflow - if there is any restriction or blockage or weak spot where it could collapse under light vacuum - it could cause the problem.
Overflow - blocked or restricted passage could cause this. When this presents in the winter itís a good idea to check for ice, water may have been added to the overflow tank.

You can check for clear passages and lift up the one way valve on the cap to check if itís stuck. If you see it collapsed again you could pull off the hose at the radiator and see if the hose fills, this will tell you if itís in the cap or elsewhere. I'll try to the reply shorter next time.

gold knight
12-30-2008, 07:39 AM
A little hijack but still coolant related, I figured I'd add it to your thread. I was doing a routine check of all fluids the other night. Over the course of 17 months and 35k miles I have noticed coolant in the reservoir has lowered about 2".

I opened the cap and couldn't see anything in the radiator as far down as can be seen in that little slit. Anyway, for some reason it seems to have stopped pulling coolant back into the radiator (and like I said it's only 2" below the max full line).

I used a (clean) kerosene hand pump to fill the radiator back up from the res. By the time it was completely full, the coolant was at the minimum level several inches down on the reservoir:confused:

Since reading your post, I'll refill the reservoir, check the cap and watch for the hose collapse thing too.

12-30-2008, 07:45 AM
Odd, definitely keep a close eye on temps.

FWIW I know every time I go wheeling I lose a few inches out of the res bottle due to been at odd angles etc and it just pours out.

12-30-2008, 07:47 AM
sounds like the hose is collapsing. Maybe just get some hose from the parts store and replace it and see if that does it. That's cheap trouble-shooting

12-31-2008, 12:08 AM
X2 on the coolant loss due to off roading. If I am jumping at the sand dunes I could usually open the hood and see where some came out. It’s not alot at once but adds up over time.

If the radiator has air in it and the reservoir still has fluid (preventing air from entering through there) then the air must have entered through a sealed part of the system. A collapsing overflow hose will definitely increase air entry due to the vacuum created.

Another possibility could be the over flow hose not sealing properly and letting air in (under the normal vacuum that pulls the coolant from the overflow). If this were the case I have had good luck with applying gasket sealant to the over flow hose ends but they must be cleaned first. But given that other people have had the radiator hoses collapsing (indicating a problem with the path from the overflow tank to the radiator) this seems less likely the problem or only problem.

There are also many other possibilities but given that people have had radiator hoses collapse it seems like checking the path to the overflow tank is a good starting point.

I'm curious about pulling my hose off and seeing how readily it collapses under vacuum.