To further "truth", I'd say no one has articulated why one system is used over the other, or why one is better than the other. From a number of posts, I've read other auto mfg's use the so-called "closed" system as well as the early XJ. So why the differences? And, exactly what is a closed vs open system?
In the "olden" days, most (all?) cooling systems were closed. The expansion "bottle" was built into the radiator. When you filled a radiator, you did not fill it to the top; you left an air space to accommodate coolant expansion. Also, in all of the cases I've worked with over the years, the top of the radiator was always higher than the engine. This does not seam to be true any longer. The XJ's "closed" system uses an expansion tank located on the firewall, at a point insuring it's the highest point in the cooling system. The other system, which many on this board refer to the "open" system, really isn't open. The expansion function is just dealt with differently, using more moving parts than the early XJ system. The ability to cool the engine is the same in eather system, and the thing that irritates me the most is when someone complains of over heating, the first cry in resolving the over heating problem is to "modify
that piece of shit "closed" system. Now, I also had the closed system on my XJ before swapping engines, and I too, had problems with the plastic expansion tank. The only time I ever had overheating was when the bottle cracked, releasing coolant, or the new-style pressure cap would not properly seal, releasing coolant, and once, when my tired radiator became partially clogged. Now it's obvious, in any one of my cases of over heating, converting to the "open" system would have solved my problem, just like installing a new engine will solve my noisy lifter problem (if I had one); however, replacing the faulty component also solved my overheating problem, at a fraction of the cost and time it would take to change out the complete cooling system. Again, how about some real tech talk on the differences.
