Closed to Open Cooling System

[bajajunkie]

I just found out bout the closed and open cooling systems that are out there on the pre 90' mj and xj. I have searched through here naxja and pnwjeep to find as much info on this as possible.

 

here is what ive gathered.

 

the closed system is a presurized system that uses a temp switch in the t-stat housing to control the electric fan and causes much headache as far as maintenance goes.

 

the open system is well ( I would say) "normal" cooling system.

 

I know alot of guys convert from the closed to open systems and i plan to do this myself.

 

here are the questions:

1. why in the world would someone want to stay with the closed system? it just seems like one more thing to worry about and way more complicated than it needs to be.

 

2. besides swapping out the radiator and putting in a reservoir what needs to be changed? new t-stat housing? temp switch to control electronic fan?

 

thanks for any attempts to clear this up.

 

oh and i remember reading a DIY thread on doing this. can't remember if it was here or elsewhere but it didnt seem very clear and it was way too rediculous considering he spent like $150 ("high-Flow") on a $15 t-stat housing he could get form napa.

[ratrapp]

the fan switch is actually in the radiator

[terrawombat]

No temp switch in the t-stat housing for a closed. That came around on the later XJs, but I don't know which year.

 

Here is how I converted to an open system for about $50. It can probably be done cheaper with junkyard parts.

 

Keep the closed system radiator. Buy a universal filler neck and splice it into your upper radiator hose. People swap to an open system radiator because they either already have one, can get one real cheap at the junkyard, or simply didn't know a universal filler neck was available. Here is the one I got: http://www.amazon.com/gp/product/B000COS5OW Unfortunately it looks like it went way up in price. I paid $24 shipped for it. I also had a relatively new radiator in my MJ so that's why I didn't want to get rid of it. I'll admit, swapping to an open system radiator is a much cleaner look. You'll also need a radiator cap - I had a couple lying around so no cost there. Also had hose clamps from another project.

 

I bought a universal coolant overflow bottle kit from Auto Zone. I think it was about $20 for the whole kit and it came with everything I needed. I mounted it right in place of the old expansion bottle.

 

I also needed longer hoses to reach my heater core. I had those lying around and I don't remember what the dimensions were, but I do remember one was larger than the other.

 

As to why people want to keep the closed cooling system...because it still works or they don't know that they CAN convert to an open.

 

Here is a pic of my finished product:

 

 

Oh, and my MJ went from consistent 210-230 degree operating temperatures to consistent 190-210 degree temps after the switch.

[ParadiseMJ]

here are the questions:

1. why in the world would someone want to stay with the closed system? it just seems like one more thing to worry about and way more complicated than it needs to be.

 

2. besides swapping out the radiator and putting in a reservoir what needs to be changed? new t-stat housing? temp switch to control electronic fan?

 

thanks for any attempts to clear this up.

 

The closed system works fine if it's properly maintained, has no leaks and has no air in the system. The pressure bottles crack, and the caps lose their seals fairly quicky. The same system is used on 80's and 90' era Volvos. My Volvo GL never overheated, just a better bottle IMHO.

 

You need to swap radiators, and heater control valve (if you decide to keep it at all).

You do NOT need a new t-stat housing, because there is no switch for the fan, at least there.

 

HO Open system = Temp sensor (which tells the computer when to power the fan as well as adjusts fuel/air mix.) Temp sender (which tells you what your coolant temp is via the gauge)

 

RENIX

Temp switch (located in the radiator of a closed system radiator)

Temp sender (back of head, for the gauge)

Temp sensor (lower driver's side block for the computer, air/fuel etc.)

 

96? or 97+

 

Just one sensor in the t-stat housing for everything.

 

I

[Pete M]

Oh, and my MJ went from consistent 210-230 degree operating temperatures to consistent 190-210 degree temps after the switch.

 

The higher the temperature, the more efficient the engine can burn. the big advantage of the closed systems. you can run a higher operating temp. lots of makes and models have used it. My neighbors Caddy had a closed system.

 

I kept my closed system but did get a late model radiator (wth the built in rad cap for easy filling) when the old one went south.

[Eagle]

here is what ive gathered.

 

the closed system is a presurized system that uses a temp switch in the t-stat housing to control the electric fan and causes much headache as far as maintenance goes.

Incorrect. There is no fan control switch in the thermostat housing. Even if there were, how would it cause any maintenance issues?

 

The electric fan is only the secondary, and a lot of XJs and MJs don't even have one. The primary fan is driven by the engine, regardless of which type cooling system you have.

 

the open system is well ( I would say) "normal" cooling system.

Define "normal." Both systems use a radiator, a fan (or two fans), and a thermostat. I'd say they are both "normal."

 

here are the questions:

1. why in the world would someone want to stay with the closed system? it just seems like one more thing to worry about and way more complicated than it needs to be.

Why is it more complicated? My question back to you is, "Why in the world would anyone go through the trouble and expense of changing to the 'open' system when it has the exact same size radiator and doesn't cool any better?"

 

2. besides swapping out the radiator and putting in a reservoir what needs to be changed? new t-stat housing? temp switch to control electronic fan?

Control for the electric fan.

 

Many who do the swap also change out the heater control valve.

[Naterenfo1]

Oh, and my MJ went from consistent 210-230 degree operating temperatures to consistent 190-210 degree temps after the switch.

 

The higher the temperature, the more efficient the engine can burn. the big advantage of the closed systems. you can run a higher operating temp.

 

I kept my closed system but did get a late model radiator (wth the built in rad cap for easy filling) when the old one went south.

 

I am not sure if this information applies to gasoline engines as well- but for diesel, this is how it goes:

Yes, while having 210-230 cooling system temp is more efficient for fuel burn and power transfer for your engine, you also risk damaging your engine. For diesels, if you have coolant temps over 230, you have SERIOUS damage going on to your engine. cracked/warped cylinder heads, block damage, piston lock ups etc. In a perfect world, coolant temperature would be around 180-190 degrees F. According to engine manufacturers, that is the temperature the engine is most efficient at burning fuel, and cooling.

 

correct me if I am wrong, but that's what I know!

-Nate

[Pete M]

210 is the normal operating temp for a renix era 4.0L. and it's perfectly typical for it to fluctuate up to 220. Different engines will have different requirements for the upper temp limit for the parts inside. :thumbsup:

[terrawombat]

Why is it more complicated? My question back to you is, "Why in the world would anyone go through the trouble and expense of changing to the 'open' system when it has the exact same size radiator and doesn't cool any better?

 

I know this question was for the OP, but I'll take a stab at why I went through the trouble and expense of switching to an open system. I went through three of the closed system pressure/expansion bottles, multiple caps for the bottles and a series of clamps only to have the same 210-230 degree temperatures. The closed system works when all of the components in the system are in perfect harmony with one another. With an open system, I have one less component to worry about with that pressure bottle. My open system overflow bottle doesn't care if the hoses are clamped tight or the cap is on snug.

 

Pete - while I completely understand the higher efficiency of running an engine hotter - when I put a brand new 190 degree thermostat in, I want the engine to hover right around 190 degrees, not around 210-230. On the hottest summer day with the A/C on, my closed system Renix was nearly in the 'red' zone on the gauge. Too close for comfort. I'll take the few MPGs less over running the risk of damaging my engine.

[terrawombat]

210 is the normal operating temp for a renix era 4.0L. and it's perfectly typical for it to fluctuate up to 220. Different engines will have different requirements for the upper temp limit for the parts inside. :thumbsup:

 

Since when? The FSM for a Renix-Era XJ lists the standard temperature as 192-198*F.

[Pete M]

 

the t-stat dictates when the radiator starts getting flow, not the upper limit of the temp range.

 

 

210 is the normal operating temp for a renix era 4.0L. and it's perfectly typical for it to fluctuate up to 220. Different engines will have different requirements for the upper temp limit for the parts inside. :thumbsup:

 

Since when? The FSM for a Renix-Era XJ lists the standard temperature as 192-198*F.

 

that's the first I've ever heard those numbers. heck, not one of my 4.0 MJs (3 of them including the one I sold) has had an e-fan that kicks in before around 220.

[terrawombat]

The E-fan switch is set to around 220*F, but that doesn't mean that's a normal operating temperature. The E-fan comes on when the mechanical fan can't do the work and the truck goes into 'OH CRAP WE'RE A HEATIN' UP" mode.

[terrawombat]

 

I'm not positive that this is the FACTORY service manual, but it is a service manual of sorts...

[Eagle]

210 is the normal operating temp for a renix era 4.0L. and it's perfectly typical for it to fluctuate up to 220. Different engines will have different requirements for the upper temp limit for the parts inside. :thumbsup:

 

Since when? The FSM for a Renix-Era XJ lists the standard temperature as 192-198*F.

No, that's the range at which the thermostat opens. The sender for the dashboard temperature gauge is not located anywhere near the thermostat; it's at the back of the head, which is a hotter location. Even when brand new (and I own three Cherokees with the 4.0L engine that were bought new) the normal operating temperature as indicated at the gauge is 210 degrees.Don't forget that the purpose of a thermostat is to keep the temperature UP, not down. A 195-degree (nominal) thermostat is supposed to keep the engine operating at a minimum temperature of 195 degrees.

 

Too many people get this backwards and think the thermostat's role is to establish a maximum temperature. Not so.

[HOrnbrod]

The E-fan switch is set to around 220*F, but that doesn't mean that's a normal operating temperature. The E-fan comes on when the mechanical fan can't do the work and the truck goes into 'OH CRAP WE'RE A HEATIN' UP" mode.

 

Exacerly. I replaced the power robbing mechanical fan with a 10-blade 97+ XJ electric fan. This fan is now my primary cooling fan and is set to come on at 195* LO speed, then 215* HI speed by an external controller. 99% of the time it runs at LO speed, or not at all in cold weather. IF environmental/hot/stuck-in-traffic conditions warrant additional cooling, then the stock E-fan then kicks in at about 220*, or when I use the A/C. It's a good setup and works better than the original mechanical + one E-fan setup. :cheers:

[RDAN1]

Exacerly. I replaced the power robbing mechanical fan with a 10-blade 97+ XJ electric fan. This fan is now my primary cooling fan and is set to come on at 195* LO speed, then 215* HI speed by an external controller. 99% of the time it runs at LO speed, or not at all in cold weather. IF environmental/hot/stuck-in-traffic conditions warrant additional cooling, then the stock E-fan then kicks in at about 220*, or when I use the A/C. It's a good setup and works better than the original mechanical + one E-fan setup. :cheers:

 

This setup sounds very good. Questions: What controls the 10 blade electric fan? also, can this setup be used with a closed system on an 88 4.0 ? if so what other mods would be required?

[HOrnbrod]

http://www.comancheclub.com/forums/viewtopic.php?f=9&t=8342&hilit=electric+fan