1998 GC w/ 4.0 / auto

Last April saw a drip hanging from water pump vent hole. Replaced water pump, idlers, and belt. Ran about an hour - header blew off radiator. Replaced radiator, hoses, thermostat, and cap. Drove around town - maybe 200-300 miles. Left Jeep in Florida.

Started Jeep last Saturday when I got back to Florida. Within a minute the belt flew off - unbroken. Turned out to be due to a harmonic balancer coming apart. Replaced that and reassembled. Installed the external regulator kit I bought last winter. Except for one electrical fitting. Drove a mile to Auto Zone, got the add-a-fuse widget. Came out and antifreeze was pouring out. Hoses and overflow all dry - PS header tank is apparently leaking (I can't remember which side blew off the last time).

Engine never overheats - runs just over 200 degrees all the time.

The new/failed radiator has a lifetime warranty so I went to get another new one but my job ain't changing radiators every few hundred miles. Anybody have any ideas? What could cause this nonsense? What might prevent it in the future? I forget the brand of the radiator but I got it from O'Reilly as Auto Zone didn't have one in stock at the time.

PHM
------------------

 

What pressure cap are you using?

 

I will look at the actual cap in the morning but it is the standard pressure - according to the vendors. It strikes me that it seemed high when they gave it to me and that made me ask them to re-check it.

But when I suggested using a lower pressure cap they seemed to balk - saying that it might cause overheating. (Or maybe overflowing - I wasn't taking notes). But in any case; They advised against using a cap lower than the OEM spec.

PHM
--------------

 

Sounds to me like you might need a flush. It certainly won't hurt anything to do it. Also maybe water pump issue?

 

Radiator not mounted correctly.

 

Not mounted correctly how? I mean, its not rocket appliances, and how would it being mounted incorrectly cause this? Upper hose runs into the t-stat housing. A hose runs from that to the heater core, from the heater core to the water pump. Lower radiator hose to the water pump.


Honestly, if youre actually blowing out the radiator, Ive got nothing. It makes no sense to me if the hoses are all hooked up correctly, which again, is REALLY hard to screw up.

 

That last person you trust is the vendors because they religiously stick to what their computers tell them and these computers are wrong a LOT. I have to second guess them all the time. Just happened yesterday with a fuel filter, If I hadn't looked and told them it was the wrong one I would have made a 150 mile round trip to the parts store for nothing.

I'm running a 13 lb cap in the second hottest place in the US and have never had it boil over and spit any out. And I wheel in first gear low range for miles and miles at a time in the dead of summer out here. Coolant mixture is way more important than cap pressure.

I'm not for sure exactly what these are supposed to have but a 14 lb is probably more than enough in any environment. Overheating is usually caused by other problems, the cap just relieves the pressure once it has already overheated so that the other problems don't blow up the radiator or pop a hose too.

 

My '96 calls for 16lb. I believe your '97 does to.

 

You are probably right and I think this holds true with most current makes and models, but this higher pressure trend was started back before plastic radiators. But I now know for sure it's not needed and I feel much safer with a lower pressure cap if it is working fine because of these plastic radiators. Honest... Never had a "shut off boil over" pressure issue with mine at all using the 13 lb cap. And my environment would be the ultimate test for sure!

 

Actually specs read 14-16lbs. Earlier XJ's called for 13. So we're good across the board.

 

Thank you for chasing it down! Nice to know I wasn't totally wrong with my concept! lol

 

3 PSI difference in the cap pressure is not going to cause the problems you have. The plastic tanks are known to be a failure point in all radiators that use them. Yes, they can be reliable for a ton of miles, but when they let go, thats it. It is possible that the new radiator was defective. Again, all too common. However, if you replace it again, i would get to a mechanic or see if you can borrow a tool to measure the pressure in the cooling system. If you have a head gasket issue, cracked head, etc. it is possible that it is overpressurizing the system. If that is fine, I would chalk it up to bad replacement parts and motor on

 

They sell 18 to 22 pound caps. Get a hold of one of these and you very well could be in trouble with a plastic radiator.

But you are absolutely right. If it has a habit of blowing tanks or pressuring open any cap rating it could be a compression issue.

This would be an even more important reason to make sure it pops the cap before it pops the radiator.

 

The cap is what O'Reilly gave me when I bought the original new radiator in April - 18 lbs.

Today I returned the warranty radiator and asked them again. They repeated: 18 lbs.

Think I should change to a lower pressure cap? Or will that reduce the cooling effectiveness in some way?

How low a pressure can I agreeably run and still be OK?


PHM
---------

 

I would go to a 14 no matter what they tell you. And if it spits fluid out, then you have other problems because it shouldn't at all with even a 14. Like I say, I am running a 13 lb in 125 degree conditions without any problems at all.