mhead
NAXJA Forum User
- Location
- Encinitas, CA
Watchout for the after-market radiator overflow bottle on pressurized cooling systems used on 4.0 Jeeps prior to somewhere around 1991.
I don't know where the bottle I have has come from but I suspect they are all the same. The cap on the bottle does not have continuous internal threads but has 4 groups of threads and 4 reliefs for overflow to exit from the cap pressure regulator. Unfortunately these reliefs allow the cap to flex. If the cap is tightened strongly the 4 groups of threads will slip over the bottle threads.
The problem is this: The cap can be tightened to a torque that seems reasonable and one that does not allow radiator fluid to pass under the cap seal. This is to say that the cap can be put on in the normal way.
BUT... when the engine is run at first things seem OK. The cap seems to hold radiator pressure OK. But as the bottle and the cap heat the cap plastic softens and POP! the cap slips on the threads and now it's one complete turn loose. All the radiator fluid will escape and if you are not watching the temperature gauge like a hawk the engine will in just a few seconds overheat to it's death. Don't ask me how I know.
The fix is to tighten the cap acceptably, THEN place a hose clamp around the cap and tighten. The hose clamp being metal will reinforce the cap so even if it softens a little it can't slip over the threads.
Or I suppose you could purchase the bottle from the Jeep dealer, for $90+ for the bottle and $25 for the cap. I've called the dealer recently on a couple of items and it seems their prices have skyrocketed. Maybe the new owners? Also I suspect, without proof, that the dealer parts are simply re-marked parts from Pep Boys.
The after-market cap I have, and the one that I purchased from the dealer, were both plastic, felt like high density polyethylene like the bottle. Both had the problem. Someone help me out here: I vaguely remember the caps being a bakealite (sp?) or some really hard plastic. Anyone have a 20 year old cap to examine? What's an original cap made from?
I don't know where the bottle I have has come from but I suspect they are all the same. The cap on the bottle does not have continuous internal threads but has 4 groups of threads and 4 reliefs for overflow to exit from the cap pressure regulator. Unfortunately these reliefs allow the cap to flex. If the cap is tightened strongly the 4 groups of threads will slip over the bottle threads.
The problem is this: The cap can be tightened to a torque that seems reasonable and one that does not allow radiator fluid to pass under the cap seal. This is to say that the cap can be put on in the normal way.
BUT... when the engine is run at first things seem OK. The cap seems to hold radiator pressure OK. But as the bottle and the cap heat the cap plastic softens and POP! the cap slips on the threads and now it's one complete turn loose. All the radiator fluid will escape and if you are not watching the temperature gauge like a hawk the engine will in just a few seconds overheat to it's death. Don't ask me how I know.
The fix is to tighten the cap acceptably, THEN place a hose clamp around the cap and tighten. The hose clamp being metal will reinforce the cap so even if it softens a little it can't slip over the threads.
Or I suppose you could purchase the bottle from the Jeep dealer, for $90+ for the bottle and $25 for the cap. I've called the dealer recently on a couple of items and it seems their prices have skyrocketed. Maybe the new owners? Also I suspect, without proof, that the dealer parts are simply re-marked parts from Pep Boys.
The after-market cap I have, and the one that I purchased from the dealer, were both plastic, felt like high density polyethylene like the bottle. Both had the problem. Someone help me out here: I vaguely remember the caps being a bakealite (sp?) or some really hard plastic. Anyone have a 20 year old cap to examine? What's an original cap made from?
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