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broken_down
07-13-2007, 03:03 PM
I have a 1990 xj 4.0 litre HO with the reservoir cycle style cooling system set-up.

My Question is why does the cannister always boil over when I turn the truck off. When I'm driving the temperature gauge stays between 40 - 100 degrees. Doesn't boil when it's running either, only when I turn it off....

Any suggestions on what is going on?????

jeeper
07-13-2007, 03:07 PM
change your rad cap -its a pressurized one with the bleedoff -its prrobably just getting week at the spring

Caribourob
07-13-2007, 03:24 PM
Good call jeeper. I'll just add that when you shut the engine off it actually gets hotter before cooling down since you stop the flow of coolant with the mechanical water pump. Coolant and/or water will boil at a certain temp and the pressure in the cooling system raises the boiling point. So, as Jeeper says, you seem to be losing pressure, thus reducing the boiling point and showing up in the resevoir.

broken_down
07-13-2007, 03:33 PM
Thanx for the info guys! Hopefully this works...

Leithmc
07-13-2007, 03:36 PM
I think he's describing an expansion tank/closed system. Is there a tank on the firewall instead of a rad cap? If so you could have a small crack in the tank allowing the pressure to bleed off and allowing the coolant to boil.


Leith

Caribourob
07-13-2007, 03:36 PM
Let us know so we can gloat about our mechanical wisdom.:party0010:



Or learn to shut about it cause we really don't know fuck-all.:confused0006:

ha ha ha.:happy0045:

broken_down
07-13-2007, 04:30 PM
Let us know so we can gloat about our mechanical wisdom.:party0010:



Or learn to shut about it cause we really don't know fuck-all.:confused0006:

ha ha ha.:happy0045:

Well you can allow for your head to grow for now. I bought a new rad cap just waiting for the engine to cool off. we'll see if it works. I hope so
:party0010: [cheers]

jeeper
07-13-2007, 04:51 PM
Well you can allow for your head to grow for now. I bought a new rad cap just waiting for the engine to cool off. we'll see if it works. I hope so
:party0010: [cheers]

I hope you hgot the right cap as theres two kinds -one for with a resevoir and ones for no resevoir !

broken_down
07-13-2007, 04:58 PM
yup bought the right cap. Going to put it on right now. keep my fingers crossed!

Pudge
07-13-2007, 06:10 PM
do yourself a favour and upgrade your rad to the open system style. I have a 90 as well and did it about two months ago, and drove to the interior recently with no probs, should have done it long ago. Before I did that I replaced the tank (was ready to go again) and cap, and thermostat, checked for cracks/leaks, etc... nothing kept it cool till I upgraded and added an extra electric fan.

good luck
Paul

broken_down
07-13-2007, 06:48 PM
It's working for now, new cap holds the pressure better. If it starts to act up again than I'll probably swap to a normal radiator open system.....

Thanx to everyone for all there input

:party0010: [cheers]

trex300
07-13-2007, 07:45 PM
I swapped out the closed system in my 88 for one from a 91 with a rad cap...haven't had any problems since. Straightforward swap with Pick-a-part pieces -$40 total.

kootenaycat
07-14-2007, 12:23 AM
I did the upgrade on my '90 as well when my pressure tank developed a crack. Bought a new wide row 2 core, biggest cores they made, cost me less then $200 for a new rad. Wouldn't even mess with a used unless you get it checked first. I also installed an electric fan (where the factory AC one goes) and have not had to use it yet. Nice for a backup though.

broken_down
07-14-2007, 12:49 AM
Truck is still running strong and cool since I put in the new cap..... Time to hit the trails on saturday. Can't wait!

:party0010:

Fuzzydog
07-14-2007, 02:53 PM
IMHO the closed cooling system gets a bad rap. My Audi has a closed system and works just great, and that sucker gets a lot hotter than my XJ.

I have found that every single XJ with the closed system has a tear in the hoodliner and scratched paint on the underside of the hood right above where the overflow tank cap is. The hood hits the cap, breaks the threads on either the cap or the tank and then it won't seal tight. shortly after buying my XJ I replaced the cap and tank and all was fine for a week then started boiling over again. that's when I looked closer and realized what the problem was - so I removed the tank and bent the bracket down and got another new tank and cap. no problems since then

I'll tell you what is really STUPID - its having a rad cap on a 90 degree elbow sticking out of the plastic end tank on an alum/plastic rad. that is crazy! every time you check your coolant level you are pushing down on that elbow and stressing it. I recently replaced my rad and I did get an open system rad with the cap on the rad but I don't use it for now - I still have my expansion tank and check my coolant that way.

broken_down - I strongly suggest that you look at your hood right above the coolant tank and if there is the marks showing contact, bend that coolant tank bracket downwards before you wreck your new cap. I'm just saying.....

broken_down
07-15-2007, 12:41 PM
I'll check that out, Just got back from camping this weekend with no cooling problems.