Open or closed cooling system discision

After replacing my blown motor in my '87 XJ, installing new water pump, thermostat, and radiator, I had two weeks worth of overheating and having to burp my truck. I reviewed the countless threads covering open and closed systems. I wanted to keep the cooling system stock, but decided to cross over. I took out the expansion tank and all the excess hoses, and made it straight to and from the heater core. Haven't had a lick of trouble!

Huh, my closed system has been fine for 19 years. Then again i decided not to abuse my truck...

after replacing my worn out motor in my '88 XJ, installing a new water pump, thermostat, and radiator, I had two weeks of...... no problems. I know the non-vented system is unusual, but if you work with it- it'll bleed like any other. I filled it 'till it leaked from the bottom hose, then tightened it-- I filled it 'till it leaked from the H2O pump, then tightened it-- so-on 'till I got to the temp. sensor in the head. I filled 'till it came out there and closed off everything else. I filled the rest and ran it for the first time-- 2000 rpm for about twenty min without any problems-- kept filling from open surge tank and no problems-- never got hotter than 210deg and runs like new after 5000 miles of easy driving. 7500miles and pulls like an 8cyl (at least like a new 4.0l)
Top temp recorded after breakin was 220deg. in 94deg temps after 25min at dead stop in traffic. I stopped and got dinner after that- ran cool as poop when I went out to leave!!!!!

The new Ford's and Chrysler vehicles all come with Closed Cooling Systems (Don't know about GM or the imports). It almost seems Renault/Jeep was ahead of its time.

Granted, I never had a closed cooling system, and looking at it, I would worry about the durability and longevity of that plastic bottle exposed to the pressure and heat of the cooling system. And judging from the posts, that does seem to be the weak spot of the system.

As well, I don't see how an open system (if the coolant recovery is working properly) would be an different than a closed system in performance and durability. Keeping the plastic expansion tank isolated from the heat & pressure of the cooling system seems to me to be a good thing. As well, I do like the ability to open the pressure cap on the radiator and look inside it to judge its condition.

But, the big manufacturers wouldn't switch to another system if there wasn't a good reason. Whats the benefit of the closed system over the open system?

I tend to favor driving older vehicles as I find them interesting and enjoy working on them. One thing I have found out is that the less you touch your radiator (with plastic end tanks) - the better. I have found that the plastic pressurized expansion tanks are actually more durable than the plastic end tanks on most radiators. I shudder at the thought of pushing a rad cap on and off a plastic tanked radiator. It is doomed to cracking.
both my current 17 yr old XJ and 19 yr old Audi have pressurized expansion tanks and as long as they are in good shape, it is an excellent system.

One thing I am going to do to the jeep though, is replace the maze of rubber heater/expansion tank hoses with copper line for less chance of failure out in the bush

Rick Anderson said:

The new Ford's and Chrysler vehicles all come with Closed Cooling Systems (Don't know about GM or the imports). It almost seems Renault/Jeep was ahead of its time.

Granted, I never had a closed cooling system, and looking at it, I would worry about the durability and longevity of that plastic bottle exposed to the pressure and heat of the cooling system. And judging from the posts, that does seem to be the weak spot of the system.

As well, I don't see how an open system (if the coolant recovery is working properly) would be an different than a closed system in performance and durability. Keeping the plastic expansion tank isolated from the heat & pressure of the cooling system seems to me to be a good thing. As well, I do like the ability to open the pressure cap on the radiator and look inside it to judge its condition.

But, the big manufacturers wouldn't switch to another system if there wasn't a good reason. Whats the benefit of the closed system over the open system?

Click to expand...

I was going to say (so I will say it) that the open system is exposed to oxygen and CO2 which disolves in the liquid coolant in the overflow bottle, then it is dragged into the cooling system overnight. CO2 forms carbonic acid when it disolves in water, and disolved oxygen in the coolant promotes oxydation, rust.

I hear (and it makes sense) that the closed system breaths gas in and out too, so it may be no different as CO2 and O2 would be dragged in there as well. Maybe it has more to do with the difference in the cap and the breathing process itself. Gas is not going carry or produce solids that can build up in the vent area. An open system can see a build of solids in and around the cap sealing area, in the vent liine and at the bottom of the overflow bottle which can eventually hange up and hold the radiator cap open and keep it from sealing properly.


I think one of the tricks to burping that many miss is to initially run the system with the plastic bottle cap off, and to fill the bottle to the fill line periodically as it burps, then once the level is stable put the cap back on. That was all I did with mine and I had no problems. I did that right after replacing the bottle and radiator and hoses, just once.

To burp or not to burp. I spend enough time burping my 4 month old daughter, not going to give my truck the same babying.

Closed cooling system > Open cooling system

I grabbed this expansion tank from a 1997 Lincoln TC, cost me $5.:gee:

Slo-Sho said:

Closed cooling system > Open cooling system

I grabbed this expansion tank from a 1997 Lincoln TC, cost me $5.:gee:

Click to expand...

do you have heat?

Heater core is bypassed for the summer time. It lets my A/C cool much more efficiently w/o boiling hot coolant right next to the evap core.

*update*

I had to hook my heater core back up as the weather is getting cooler now.
My custom closed cooling system has been great thus far and NO, that is not garden hose, it's silicone hose used on the police package Vic's.
Closed cooling system 4LYF.