Cooling system questions

[90 work truck]

I bought my Truck 2 years ago, not knowing what/how the po handled maintenance did a lot of maintenance right away changed filters, fluids etc.

 

Then this winter noticed the truck was running cooler than normal bought a laser thermometer(truck has idiot lts) and haven't been able to find a gauge cluster locally)

 

Put a Macs pressure bottle in last year when the plastic one developed a crack and the cap had issues, then this winter in trying to solve my under heating issues Put in a 195 degree Mopar stat & deleted the Vacuum actuated heater control valve.

 

All of that with the help of  the folks here have got "Old Paint" a lot closer to Normal, now I'll get on to my question:

 

Don't know if it was because of now I have a system under pressure or it was just time, now the radiator has a small leak, I've read all the topics I could search for here & Google and it seems like the Mod of choice is to convert from a closed to open system.

 

I'm thinking that I already have an "Open" system as the Macs Bottle has the missing radiator cap, when I did the deleting of the HCV I used Copper plumbing Ts with sleeves for the larger heater hose, not a pumber (Hot On Left, cold on right and Crap flows downhill) but no leaks.

 

So the only advantage I can see by "Upgrading" to a 92+ radiator with a cap, would be getting rid of the Ts, then I could use the Macs as an overflow bottle, guess I'd have to depressurize that cap so it would function as an over flow, or just use one of the other inlets(with larger diameter hose as the over flow..

 

Looks like an OE plastic and metal(whats n there now) is less expensive and I'm just wondering if I'm missing something?

 

The Mac's Bottle is sitting where the oe plastic one was.

 

This is my DD and work truck, the most "wheeling" It'll see is an occasional logging road, or crossing a cow pasture to get me closer to a deer stand so its not going to get hammered on trails.

 

I would like your opinions, Thanks much,

Mark

[ftpiercecracker1]

For simplicity sake I think it's hard to beat an open system. don't have to worry about bleeding it just so or having all the extra pressurized plumbing that could spring a leak.

 

That being said, I still have the closed system. Had to buy one new pressure bottle and upgraded the cap to the Volvo unit. Also deleted the HCV. I have had this setup for years now and have never had a problem.

 

The truth is, all things being equal, the closed system actually has a larger coolant capacity.

 

The only benefit I see to switching would be for convenience and a little more simplicity.

 

Why fix what ain't broke?

 

FPC

[omega_rugal]

the closed system actually has a larger coolant capacity.

 

how is that?

[Eagle]

The installation of the Mac's aluminum tank does, indeed, convert the system to an "open" system. The Mac's bottle is not set up to function as an overflow recovery bottle. The only advantage to buying a new radiator with a cap is that you'll have a new radiator. Personally, I would (and have) replace the leaking radiator with a radiator made for the Renix years, and keep the Mac's tank that you spent good money for. If you installed a Mac's tank, you should already have added a coolant recovery bottle.

[Eagle]

 

the closed system actually has a larger coolant capacity.

 

how is that?

 

 

Becauese the surge tank/bottle on the firewall is part of the pressurized system, so that capacity is in addition to the capacity of the radiator.

[90 work truck]

Eagle, dumb question why would I need a coolant recovery bottle With the Macs pressure bottle when the cheapo plastic one just had an overflow hose to ground?

[90 work truck]

Hose I'm referring to is the smaller diam..

Hose right under cap I assumed if pressure is to high (pressure relief hose?) that is a short section that runs down near oil filter

[Eagle]

The OEM plastic bottle did NOT have a hose to the ground. If yours did, somebody had screwed with it,and that would explain why it had problems.

 

The OEM plastic bottle (and the Mac's aluminum replacement) is an integral part of the sealed, pressurized cooling system. The cap is a pressure cap, to hold pressure and thus to raise the boiling point of the coolant to around 240 degrees F. When coolant heats up, it expands. In a normal, "open" system, the radiator cap has a two-way spring valve that allows coolant to flow out to a catch bottle, and then allows the coolant to be sucked back into the radiator when it cools down. There should be NO air in the open system.

 

The factory "closed" system has no overflow provision on the pressure cap. To allow for coolant exoansion, the plastic bottle is filled only halfway when cold, and the remaining air space is to allow for expansion. There was no tube to allow coolant to dump to the ground. The Mac's aluminum tank, however, (like the Moroso aluminum tank I use) takes a conventional radiator tank and DOES have a fitting for a tube to an overflow catch bottle. Which means the Mac's tank can (and should) be filled completely rather than leaving half of it empty to allow expansion.

 

http://image.fourwheeler.com/f/8956868+w600+cr1/154_0607_01_z%2bcooling_system_buyers_guide%2bmacs_radiator.jpg

 

If someone modified your plastic tank to allow a tube to atmosphere, they defeated the purpose because it can't hold pressure when there's a vent line open to atmosphere.

[omega_rugal]

 

 

Becauese the surge tank/bottle on the firewall is part of the pressurized system, so that capacity is in addition to the capacity of the radiator.

 

 

 

 

i was under the impression that open cooling radiators have slighty larger compartiments to hold more coolant than closed ones which makes sense since the closed system has to build up pressure in order to raise the boiling point, which may take longer and/or be less efficient if the radiator had larger compartiments (more room, less pressure) in closed systems these compartiments are slim

[omega_rugal]

Why fix what ain't broke?

 

because OEM expansion tanks break easily? or that an engine like the 4.0 doens`t need it?

 

why break what is already fixed...?

[ftpiercecracker1]

 

 

Why fix what ain't broke?

because OEM expansion tanks break easily? or that an engine like the 4.0 doens`t need it?

 

why break what is already fixed...?

The first part is true, I'll give you that, but I don't follow the second part. Doesn't need what?

 

 

And just to be clear I said that because I thought your system was working as is, if not my mistake.

[Eagle]

 

 

 

Becauese the surge tank/bottle on the firewall is part of the pressurized system, so that capacity is in addition to the capacity of the radiator.

 

 

 

 

i was under the impression that open cooling radiators have slighty larger compartiments to hold more coolant than closed ones which makes sense since the closed system has to build up pressure in order to raise the boiling point, which may take longer and/or be less efficient if the radiator had larger compartiments (more room, less pressure) in closed systems these compartiments are slim

 

 

Both systems have to build up pressure to raise the boiling point. That's why that thing you screw on after you check the coolant level is called a "pressure" cap.

[omega_rugal]

but the open cooling opens at some point, the closed doesn`t right?

[DirtyComanche]

but the open cooling opens at some point, the closed doesn`t right?

 

The closed system should never vent and the XJ/MJ system doesn't really have provisions to do so.  Some modern vehicles with closed systems have provisions to vent, but it is a design feature that only comes into play in the event that the system has been overfilled.  Overfilling is something that will cause problems on the XJ/MJ system.

 

The open system doesn't open THAT much, it pukes maybe a liter or two into the overflow/recovery tank, depending on temperature and system capacity.  If you don't saturate the cooling system, IE it's cold out and you don't really load the engine up, it won't even be that much.

 

System capacities between the two are essentially the same.  There's a couple more liters of coolant being recirculated in the closed system (not less), but that's about it.  Radiator dimensions are for all purposes the same.  Since the closed system radiator is harder to source, there is many closed system rigs running around with an open style (with rad cap) radiator, they just have the overflow plugged, and it works fine.

 

I don't know if the design similarities hold true for all vehicles that can be had in both an open or closed cooling system configuration, but looking at modern GM trucks (closed system) I would say they did not skimp on the radiator/radiator tank capacity in any way.  I guess if you had a massive radiator/tanks/pressure bottle and ran a real hot thermostat, you might be able to get the coolant in the engine to above boiling before the system pressure built high enough to prevent it, but I'm not aware of anything having that issue.

[90 work truck]

I misspoke. Had a senior moment correct the plastic bottle did not have a hose that went to ground, I put that smaller diameter hose on the Macs cause I thought that's what was done on other/older vehicles I've had. Seeing how that small nipple is right below the cap and above the seat for the cap, fluid would only flow to that hose when pressure exceeds 16 psi (overheating) right? How would the Mac's pressure bottle draw coolant from bottle if spring has rubber seal pushed down to seat? Where are other users with aftermarket putting the bottle?

 

I've been using mine like the plastic one(filling it 1/2 way when cold) I've never seen anything draining from it though I have made sure that the bottom hose on the Macs is the suction and the side hose (Under the smaller hose) is the inlet so with the cap off and running I can watch fluid coming into tank,

[90 work truck]

Did some more searching here, might of answered my own questions(your previous posts did) looks like a 2.5 overflow bottle is in my future, as well as a radiator.

I like to try to know why/how things work, and I am under some misconceptions about the cap. And doing it the way I have been filing it (the mac bottle) 1/2 way at cold , I might be allowing air to enter system when sitting as the inlet to the tank is above the coolant level (when 1/2 full) Would of thought between the pressure of the system ad that being the incoming fluid it would of been good, anyhow worse that I can see is adding a quart or so of coolant to the system.

 

I'd rather not have to run a hose all the way over to airbox if I don't have to, I've relocated my vacuumed canister under the pressure bottle bracket and have a little room between the Macs bottle and the fender wall, going to look into there first.

 

Where have other people done for over flow bottle that went with the aftermarket tanks?

Thanks,

Mark

[Eagle]

but the open cooling opens at some point, the closed doesn`t right?

 

Correct. On the "open" system the radiator cap acts as a check valve.

 

Grab a radiator cap and look at it. It has a fairly strong spring that holds the gasket down against the flange inside the radiator neck. That's the pressure seal, and the strength of that spring is what determines the pressure rating of the cap. When the pressure in the system exceeds that value, it forces the gasket off the seat and allows coolant to flow through the overflow tube into the catch bottle.

 

Now we have to have a way of getting the coolant back into the radiator. See that smaller disc in the middle of the gasket? It also has a light spring on it. When the radiator is under pressure, the pressure holds that disc against the gasket and maintains the seal. When the system cools down, now the radiator goes into a slight vacuum. This pulls the small disc away from the gasket and allows coolant to be pulled back from the catch bottle into the radiator.

 

The "closed" system doesn't have any of the overflow/return provisions. It relies on the air space in the plastic bottle to accommodate the expansion. That's why the plastic bottle (if you still have it) must not be filled more than halfway.

[90 work truck]

Thanks Eagle, GREAT explanation, so correct me if I'm wrong the tube that goes to overflow from my Mac's Pressure bottle needs to go down to the bottom/lower part of the overflow bottle? Can't see the fluid jumping up to the inlet near top of overflow? That "slight suction" wouldn't be enough to bridge a 4-5" gap? Also command sense tells me the top of overflow bottle should be close in height of the Mac's bottle? Was thinking I'd have room for it under the Mac's(in front of blower motor) Experience with aquariums says that an accident waiting to happen, with all the fluid above it siphoning down into my blower motor!

 

I would need to move a lot of vacuum lines relays etch to mount it over by the airbox on the driver side inner fender.

Did some Google searches and looks like guys are making these from everything from High energy drink cans to spent whiskey bottles.

 

Does your overflow bottle have 2 inlets or a hose inside the bottle?

[Eagle]

I switched my ;88 Cherokee over to aluminum a long time before Mac's came out with the tank you're using. I used a racing surge tank from Moroso, the speed equipment manufacturer. It's a universal, so I had to troll the hardware stores to find the right fittings to make it work. I bolted a length of slotted angle to the pinch seam under the OEM tank location and then attached the Moroso tank to that.

 

 

 

 

I put the overflow catch bottle over next to the air box -- couldn't figure a better place for it, so there it is. It has been there for at least ten years, and it works fine.

 

[90 work truck]

Thanks Much Eagle, AGAIN GREAT EXPLANATION thanks for the picks!