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New XJ Owner. Questionout PO's cooling mods

matchrocket

NAXJA Forum User
Location
Utah
So, I recently purchased an 89 XJ and I am having cooling issues. (Go figure right?) I have found a TON of good documentation on the issue, but I have a question about a mod the PO has done.

The overflow tank has been replaced with an alum. unit. There is a hose going from the cap to the tank, which I would expect. What I don't understand, is the hose nipple on top of the tank not attached to anything. It looks like there was once a hose attached, but no longer. It is an open fitting into the tank. Thoughts?

I go no where.
DSC02580.jpg


I go to the bottom of the tank.
DSC02583.jpg
 
OK - so he's converted to an open system (the filler cap in the upper hose) and gone to a non-pressurised overflow (the aluminum tank.)

The 'extra' fitting up top (that has had the hose removed) is the "overflow guide" from the overflow tank - assuming the thing should fill up entirely and the fluid isn't drawn back into the radiator, this is where it will come out. The hose there would be to guide the overflow-overflow coolant from the tank around anything important - and it can be pretty much any hose that will fit on the nipple - which looks like about a 3/8" hose, going by the size of your finger and the likely thread of the thing. You don't really even need a clamp (but I would suggest pulling that fitting out and putting a "street ell" in so the hose doesn't go out straight up and hit the hood. That's probably why it isn't there anymore.)
 
OK, you answered two of my questions. Thanks! (Open or closed)

The tank was bone dry, and I was low on coolant. I added some to the tank, and the filler, but I don't suspect it will suck in. Or will it? (Still need to try the "down hill burp" trick.)
 
"Open" systems use the overflow tank for exactly that - overflow. I'm assuming that the smaller hose under your radiator cap filler goes to the overflow tank?

Your radiator cap (like 90% or so of caps out there - nothing wrong with the closed system, nothing wrong with the open system) has two valves in it. If you take it out when you re-read this, it will make more sense to you.

Valve #1 is the overpressure valve. That's sealed by the large black rubber disc against the lip inside the filler neck. The large spring is calibrated to release at the rated pressure of the cap (theoretically) - typically 6-16psig. Since things expand when they get hot, the full coolant has to relieve somehow - so it goes through this valve and into the overflow tank.

Valve #2 is the vacuum relief valve, and that's the little silver disc in the middle. That valve comes into play when the system has overflowed, and is now cooling down. At this point, a partial vacuum is created in the cooling system - this valve opens, and it draws coolant back into the system (technically speaking, it's "pushed in" by atmospheric pressure.)

Valve #1 is tested with the typical pressure tester - it should hold any pressure below rated pressure for a minimum of two full minutes, and it should release any pressure above rated pressure until it gets down to rated pressure - then hold that pressure consistently.

Valve #2 is checked more simply - take any flat, thin tool (I usually use the point of my pocketknife) and gently pry up on the edge of that disc. It should come up easily - there's not much spring pressure holding it up (it's usually held shut by system pressure anyhow.)

If Valve #1 fails to hold or to relieve pressure properly, replace the cap.
If Valve #2 does not move easily, replace the cap.
If the cap is over five years old, have a spare handy (can't hurt - it's cheap insurance.) I'll usually write the date I replace the cap on the cap itself so I know how old it is.
 
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