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Air in radiator, burp necessary?

R

rustytierod

NAXJA Forum User
Location
pennsylvania
On the '97 XJ is it necessary to burp the radiator? I've read that it isn't but just want to confirm.

Also will this system purge itself of air automatically in park or at idle? I was thinking of putting the drivers side front on a ramp or parking on a steep incline?

Thanks in advance.
 
It should self purge, just make sure the "overflow" tank is properly filled. I usually run the front end up a bit (my driveway is far from level) when I fill. I also slightly over fill the overflow tank so there is enough coolant to be drawn back into the radiator. As I also have a back flush port in the heater hose, I open it and do the initial fill until coolant comes out of the port.
 
A 97 should not need a burping. It should pass air and coolant to and fro from the radiator to the overflow tank (not under pressure). Having the T and fitting in the heater hose can't hurt either.

Being in Park or Neutral (or any gear) shouldn't have a single thing to do with it. Not related systems.
 
Thanks for the quick replies. I meant to say "running" or "off" engine to affect radiator system.

I put the drivers side up on a ramp this morning and ran it a little with the cap off. From what I understand, the coolant fluctuate between the full and add levels, between hot and cold engine states?

I found a prestone T covered in 70 year old powered rust. I'll try and clean that thing out and put it on next time. Everything seems fine the gauge goes about literally a hair over 210 at idle sometimes. Touching the intake manifold and compressor though, i swear it could be cooler.
 
200-210 is the "average" running temp for the 4.0 If your gauge reads around 210, you are fine. There can be a little inaccuracy between the sending unit and the gauge as well. Verify with an infrared point and shoot thermometer pointed directly at the thermostat housing if you are so inclined.

Yes, by design the level of coolant in the reservoir should fluctuate between the cold and hot marks (kind of hard to see but they are there along with an indent or a bump in the reservoir at those points). Should be less in the reservoir when cold, more when hot.
 
In theory... With a 195 degree T-Stat you should cycle around the 195 mark. In reality, an indicated 210 is where we run. I use the italics as the gage in the dash is displaying a voltage (the dash really contains only volt meters) provided by the PCM. Jeep gages are not world class for accuracy.

In my case, once I have the Golectric setup fully installed, I will no longer have a T-Stat. Or, for that matter, neither an engine driven water pump or fan...
 
Yeah im aware the voltages are analogous to actual physical measurements, like temp. Although the comm between PCM and dash is a digital data bus, converted to analog at the dash gauge magnet, but the sender to computer is analog voltage, right? or is there a ADC in the sender?

Why do you desire to power the main fan and water pump electrically? It will just put more load on the belt from alternator pulley no?
 
The sender is a thermistor. By measuring the current drop across it, the PCM determines the temp. Oil pressure works the same way.

Yes, a full electric setup on the pump will add to the load once the pump is running at full speed. The manufacturer of the setup has data to support less of a load overall than the mechanicals. They are claiming 13.4 hp (crankshaft) increase over running the mechanicals. Time will tell, we will see. I have a rear wheel baseline dyno run so as I make the changes, I will document and let everyone know what I find.
 
o-gauge-steamer said:
The sender is a thermistor. By measuring the current drop across it, the PCM determines the temp. Oil pressure works the same way.

Yes, a full electric setup on the pump will add to the load once the pump is running at full speed. The manufacturer of the setup has data to support less of a load overall than the mechanicals. They are claiming 13.4 hp (crankshaft) increase over running the mechanicals. Time will tell, we will see. I have a rear wheel baseline dyno run so as I make the changes, I will document and let everyone know what I find.
Click to expand...

Voltage is an across variable so I assume you didn't mean current drop. So the sender gives analog signals to the PCM. Oh and I thought thermistor transducers were used in temperature applications, whereas the oil pressure sender is a strain gauge type transducer. Right?

I really dont think the alternator is going to be that much more efficient. Wouldn't it be less, since you are going from mechanical-->electrical-->mechanical conversion plus flux losses etc? Versus the mechanical crankshaft drive. 13.4hp wow? conservation of energy?
 
Last edited:
Most Jeep thermostats have a 1/8" relief hole in them,
but if your's dosen't, then drill one. The hole allows
pressures to equalize throughout the cooling system,
especially when the engine's cold and the thermostat
is closed. Might help with trapped air too.....
 
Runnin'OnEmpty said:
Most Jeep thermostats have a 1/8" relief hole in them,
but if your's dosen't, then drill one. The hole allows
pressures to equalize throughout the cooling system,
especially when the engine's cold and the thermostat
is closed. Might help with trapped air too.....
Click to expand...

i did read that alot of the oem aftermarket ones are missing this hole. some say the premium thermostats have them. good to know. just have to straighten my unibody out before i get back to mundane radiator stuff.
 
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