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PostPosted: Fri Dec 18, 2009 8:36 pm 
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Joined: Sat Dec 20, 2008 9:16 pm
Posts: 2866
Location: Sylvan Lake, Alberta
CLOSED

http://www.olypen.com/craigh/cooling.htm

Quote:
Care and Feeding of the Early 4.0L "Closed Cooling System"

By: Craig Houghtaling
Photo: courtesy of Matt Tway

When discussing the two types of cooling systems the XJ uses, the terms "open" and "closed" are actually reversed, but have come to be accepted that way among the XJ community, so in this article I will hold to them to avoid confusion. The "closed" system refers to the one that uses a pressure (or expansion) bottle which is at the same pressure as the system, unlike the "open" system which uses a conventional radiator cap and coolant recovery bottle that is not under system pressure. One other point I will make that is not common knowledge, is the plastic coolant cap on the pressure bottle has a pressure relief valve built into it, so it is a pressure cap, even though it doesn't appear to be. There are slots in the threads of the cap to allow excess coolant and pressure to escape when the cap is screwed on.
The closed system needs to stay "closed" in order to function properly. As long as the system is under pressure, and there is no (or very little) air in it, it can tolerate temps above boiling, and continue to maintain normal operation. However as soon as any leak develops (crack in the bottle, defective cap, loose hose clamp, etc.), pressure is lost and the coolant starts to boil. Once the boiling starts, coolant is pushed out through the pressure cap, and unlike an "open" system, there is no way to recover the lost coolant, so it is replaced by air as the engine cools down. Once this happens, overheating is inevitable. Everything has to be in perfect order for it to operate normally.

There are a couple of weak points in the system. The first is the coolant bottle. Its plastic and does not hold up well to the extreme temps and pressures encountered in the 4.0 system. It cracks easily, usually around the bottom hose outlet. Also the mating surface of the filler neck/cap can become slightly distorted and prevent a good seal. The plastic cap itself is inherently weak and is also prone to failure. The most common failure I have encountered with the cap is the seal (the flat "O" ring) inside. Over time it becomes distorted and allows pressure to escape, leading to overheating. Also it is easy to tighten the cap too much, forcing the seal out of place and allowing it to leak. I found I got a very short life from the cap and had to replace it often. I highly recommend carrying a spare since they are not available from just any old auto parts store, and it's usually way out in the "boonies" when it starts to leak. This is cheap insurance.

After flushing the system, or replacing any component of it (or after an overheating episode resulting in coolant loss), it is necessary to bleed the air from the system so it will operate properly. Under normal circumstances, it might eventually "burp" itself, however usually not without an overheating episode or two.


In order to bleed the air from the system do, the following:

It is best if you jack up the rear of the vehicle in order to raise the back of the engine (this is optional, but provides a more complete purging). With the engine off, fill the system until the coolant bottle is topped off, leave the cap off and using a 13mm deep socket, unscrew the coolant temp sensor (located on the top of the cylinder head at the rear on the driver's side), and slowly start to pull it out until you hear air escaping (you don't have to pull it all the way out, it extends down beyond the threads), coolant will soon follow, at which point you screw the sensor back in and tighten it snugly. Now top off the coolant bottle if necessary, and install the cap. When the engine reaches operating temperature, the excess coolant will be forced out through the pressure cap as the system stabilizes itself. This is a normal process so don't be alarmed by the escaping coolant.


>> Warning! <<

Never, ever unscrew the temp sender with the engine running, or start it up with the sender loose in its threads! (Not even on a cold engine). It will be launched into orbit, and you will be left standing there covered in coolant, wondering where you will find another one late Saturday afternoon }:o<
(please refrain from asking how I know this!)

Other Cooling Tidbits


There is a popular misconception that installing a lower temp thermostat will help an engine run cooler, and/or solve an overheating problem. This is simply not true. The engine will still operate at the same temp regardless of what thermostat you install. The only function of the thermostat is to determine at what temperature the coolant starts to circulate through the system. It does not determine how hot the engine can get after it opens. That is a function of the system's capacity and radiator's ability to exchange or dissipate heat. Once the thermostat opens (whether it's at 195º, 180º, or 160º) the coolant starts to flow and the engine will eventually heat the system to the same temperature, it will just take a little longer with a lower temp thermostat opening sooner, and this is not what you want. Since the internal combustion engine is less efficient at sub-normal operating temps, the thermostat is designed to get the engine temperature up to normal as soon as possible. By installing a low temp thermostat, you are probably doing more harm than good. Another popular "Band-Aid" fix is a high flow thermostat and housing. This will help some, but is seldom enough to solve the inherent overheating problems of the early 4.0. Increasing flow does not always improve a cooling system's ability to cool an engine. This is why it is never recommended to remove the thermostat completely. Flow can be increased to the point where the heat doesn't have time to transfer, and in many cases can make things worse. For this reason a high flow water pump will not necessarily help either, unless the original design was too restrictive to begin with, which is not the case with the 4.0. Remember the warning about the temp sensor being launched into orbit? A stock 4.0 water pump can produce enough pressure and flow to blow the sensor out of its hole. The key to cooling is heat transfer. This is a function of coolant capacity and heat dissipation, not just the speed of the circulating coolant. It is the ability of the coolant to collect as much heat as possible while it is in the engine, then dissipate it in the radiator. The radiator is the prime component in this process and it needs to lower the temperature of the coolant as much as possible before it is pumped back into the engine. Since the coolant capacity of the engine itself cannot be increased, the radiator is the likely candidate for improvement. The 4.0 radiator was under designed from the beginning and is marginal at best. Even in perfect condition it is only adequate, and there is no margin for extreme (or even moderate) conditions. If you are having overheating problems (or just want to insure you don't), you need to increase the efficiency of the cooling system by either increasing its capacity, or increasing its ability to transfer and dissipate heat. An aftermarket radiator will do both. A 3-row radiator increases the capacity of the cooling system and exposes more coolant to the airflow at the same time.


Even the Jeep engineers admit the "closed" system was the worst mistake Jeep ever made, and in mid '91 it was dumped in favor of a conventional recovery style system. Unfortunately they did not improve the radiator much, but adding a filler neck with a conventional metal pressure cap and a coolant recovery bottle was a giant step in the right direction. If you are interested in eliminating all the idiosyncrasies of the "closed" system once and for all, consider converting your current system to the later style "open" system. All the components are a direct replacement and no modifications are required. It is well worth the $200+, especially if you tow a trailer, live in a warm climate, or are planning on having your radiator internally cleaned by a shop.


Questions or comments may be sent to:
dch@olypen.com


`48 CJ2A, `54 CJ3B, '13 Rubicon

My Willys is your TJ's daddy.....


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PostPosted: Fri Dec 18, 2009 8:38 pm 
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Joined: Sat Dec 20, 2008 9:16 pm
Posts: 2866
Location: Sylvan Lake, Alberta
OPEN



http://www.olypen.com/craigh/rad.htm

Quote:
Converting to the Newer Style "Open Cooling System"

By: Craig Houghtaling

For a little over $200 total (parts), you can ditch your troublesome "Closed" system for good.
A later style XJ radiator introduced in 1991 will bolt right in with very little re-plumbing, and provide a far more trouble free cooling system. There are a couple of manufactures that offer a heavy duty (2 row core, or larger capacity 3 row core) replacement radiator with a filler neck with conventional cap (kill two bad birds with one stone). I chose the GDI (Go-Dan Industries) radiator for my conversion because they make a high quality product and have a great reputation.
1991 was actually the changeover year, but there can be a little confusion when ordering cooling system parts since there was a lag in updating some parts manuals. For this reason the new style cooling system is commonly referred to as 1992 and later. I also recommend that when ordering parts you order them for a 1992 model. Radiators Direct and Duracore both sell the GDI (Go-Dan Industries) 3 row radiators, and will ship them to your door for $180~$200 including shipping. You can e-mail them both for a quote, giving them the info on your model, and requesting a GDI 3-row replacement w/filler neck (I found Duracore to be about $20 cheaper for the same radiator). It will work with either transmission and has the studs for the A/C condenser mounting brackets. It is truly a drop in replacement for the old 1 or 2-row closed radiator.

This upgrade will eliminate the troublesome plastic pressure bottle and the associated hoses that divert the coolant to it. For this reason you will need to order a '92 heater control valve since you will be eliminating the "T" junction that is part of the old heater valve. It is possible to plug the unused outlet from this "T", however this could become a weak point in the system and cause trouble later. The new heater valve is only around $20 and will simplify the conversion. You will also need a coolant recovery bottle, which can be placed in the same location as the pressure bottle after it and its platform are removed. This is where the factory mounts it in the post '91 models. If you have installed a K&N/air tube conversion, you can mount it in the opening left by the Air Box which is much closer to the radiator. This can be any good aftermarket bottle, or you can order a stock '92 & newer bottle from the dealer (or Leon Rosser) if you want to stick to all Jeep parts. I also strongly recommend buying three of the four heater hoses for a '92. Although you can use regular bulk hose, it is difficult to adapt the upper heater core hose to the valve due to the fact that the nipple on the heater core is 3/4" and the one on the valve is 5/8". The factory hoses will really make pluming the new valve a breeze and the end result will have a neat and tidy factory installed appearance.

There is one caveat with using the '92 radiator. It does not have the provision for mounting the temperature sensor for the electric auxiliary cooling fan on the side of the tank like the earlier model has. In '91 the sensor was changed and relocated to the thermostat housing. There are two ways around this minor problem. You can purchase an adapter that is spliced into your lower radiator hose and accepts your current sensor. Or you can install a manual switch that turns the fan relay on as desired. Since I had previously installed a manual override switch for the auxiliary cooling fan, I chose to eliminate the sensor altogether. I found that it never came on until it was too late anyway, so I didn't bother spending any more time and money adapting it back into the system.

Installation of these items is straightforward and easy. All the later model parts are direct replacements with the exception of the heater valve which has a different configuration. If you use the factory heater hoses in your conversion this will pose no problem and everything will fit into place perfectly. There is an arrow imprinted on the body of the valve housing indicating the direction of flow. Refer to the diagram for the proper orientation of the valve and the various hose connections. You will note in the parts list below that I have listed both a '90 heater hose and a '92 heater hose that runs from the heater valve to the water pump. This is because the formed shape of the hoses don't allow for easy interchangability between the years. So what you will need to do is connect the late model hose to the heater valve and the early model hose to the water pump. Then find a spot in the middle along the top where they lay beside each other and cut both hoses. Install a cooling system flushing-adapter as a splice to join the two hoses together. This not only serves as a splice, but also a convenient place to bleed air from the system. Hook up the vacuum hose that operated the old valve to the new valve and everything should operate as before. If you need some more guidance through the swap, feel free to e-mail me for details, or look at Bob Mock's article on the Pre '92 Radiator Conversion that is posted on the Cherokee America site. He has a well written article on the swap with lots of photos. however I think there might be some discrepancies with his part numbers (not sure), so better double check when ordering the parts. I have verified the heater valve part number above through the dealer, and it is correct. The important thing to remember when ordering your parts (now or in the future), as far as any parts clerk is concerned, you are buying parts for a '92 4.0 cooling system. Don't let any salesperson tell you the '92 parts won't fit your year, they are direct replacements with no modifications necessary.



Parts List:


* GDI 3-row Radiator with a filler neck: 43-2335

'92 Heater control valve, 4 port: 56005900

'92 Heater hose, T-stat to heater valve: 56004783

'92 Heater hose, heater valve to core: 55036941

'92 Heater hose, core to heater valve: 55036942

'90 Heater hose, heater valve to water pump: 52003878

'92 Heater hose, heater valve to water pump: ________

Aftermarket Cooling System Flushing-Adapter

* Optional temp sensor adapter: 83505113
(splice into lower radiator hose)
Available from Leon Rosser

* Denotes parts not available through the dealer. All other
parts are available through your local Jeep dealer.
These part numbers are courtesy of (and were verified by)
Rick Hangartner, Parts Manager at Port Angeles Jeep/Eagle/Honda.


`48 CJ2A, `54 CJ3B, '13 Rubicon

My Willys is your TJ's daddy.....


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