jamurrin

Still sounds to me like a big air bubble is trapped inside the system. The engine block and the air gets very hot even thought the water is not.

There are lots of post about burping the close system radiators on this site....buying special funnels, or jacking up the car while the radiator is open to get the air out.

jhall

Alright, I'm going to put it all back together and then burp it. I originally blew out the coolant tank while pulling a trailer through the mountains. Replaced with new tank on side of the road without knowing anything about burping. Drive less than a mile and she pegfed out again. Towed her home and changed the thermostat. She still overheated within 5 minutes. Took off the water pump and all seems to be well. Bearings are tight, blades look really good. Never had a heating issue before. I am still going to swap out my closed system with my dead 99's open. Judt for craps and giggles and the know how, I want to burp it just to do it and to see if it was such a simple issue causing this headache.
Here's the question. All of the reads say to loosen the coolant sensor and turn jeep on to push the air bubble out while filling the coolant tank at the same time. Jeep must also have the back end higher than the front. Is the sensor on my 90 going to be the one on the driver side of the radiator right in the middle? That, is my question. By the way, you people are freaking brilliant!

freegdr

Just fill thru to rad hose when no more will vgo in attach hose .Start it add water to pressure bottle as needed .Highest point on closed systems bottle not temp sender .Bottle does not get filled to leave room for expansion Bout third way ups full.If pressure bottle caps shot it will not hold pressure causing water to boil out of bottle which leads to overheating.

djb383

Cruiser......where the heck r u man.....needs some Renix "burping" help/advise. So many myths in this thread about jacking up the XJ, air getting hot but coolant not, removing sensors, etc., etc.

(a "open system" WILL NOT COOL BETTER than a "closed system" presuming everything is equal in both......it's a myth perpetuated on the 'net that "open" cools better than "closed")

freegdr

Hes taking a power knap...lol...Ive had my 89 16 years no never took sender out ever to fill my old system.

djb383

ROTF,LMAO!.......does your XJ's cooling system have a 16 year old "belch" just dying to get out because u haven't removed a sending unit/sensor or jacked it up?

jhall

Confusion has definately set in boys. My mind is just like my old coolant tank, "BLOWN".
When it overheats the coolant in the tank doesn't boil out, it doesn't even boil.
I'm lost.
So you two are saying that an open system is no better than a closed system and that burping is pretty much a myth?

jhall

I'm not comprehending these directions. Im a tad bit dumb.

freegdr

Remove top radiator hose from thermostat housing pour coolant in hose until no more will go in. Is gonna take a little time and patient .When no more will go in install hose back on housing and tighten clamp. Now pour coolant in pressure bottle until it stays a little under half full. Start an add if needed. Install cap should be good.

djb383

A huge myth that just continues to be perpetuated on the 'net/in forums. Think about it.......the cores of the 2 rads (open vs closed) r identical. So, a closed rad in good shape will extract heat from coolant just as effectively as a open rad in good shape. Again, the rad cores are the same.

The main functional difference between the 2 systems is the bottle(s). Closed system, the bottle is closed to the atmosphere thus pressurized as the motor warms up. Open system, the bottle is open to the atmosphere, or not pressurized. Only the bottle is not pressurized in a open system, the rest of the cooling system is pressurized. Again, it's all about the bottles.

In either system, the front of the motor is higher than the rear. Air in a liquid will always move to the highest point, in this case, the front of the motor because the front is highest. In a closed system, the moment the motor starts, both coolant and air are expelled from the front of the motor (head) via the bypass port beside the t-stat and air and coolant separate in the bottle. In a open system, both air and coolant flow the moment the motor is started and exit the head via the bypass port beside the t-stat. Pressure must be released by the rad cap in order for coolant and air to flow to the bottle, where they separate. That's what both bottles do......hold reserve coolant in the bottom from the separated air in the top.

I never have understood why one would recommend making the low end of the motor the high end, by jacking it up. Makes no sense at all.

freegdr

No notice I said old system.After my third bottle cracked I upgraded....No more bottle for this guy...lol....And neither system perfoms different from the other. But both must be in good working order to cool .

djb383

Yep, I understand about the seemingly flawed Jeep/Chrysler designed closed system plastic bottle and cap. My guess is, the bean counters nixed quality plastic in favor of the cheap plastic. It just seems that the myth is,,,,,,,,,,"open" cools better than closed, and again that's just a myth 'cause it don't.....they cool equally well, all else being equal.