Jeep overcooling?

[KellenNold]

1985 XT 600

Hey, I have a 89 cherokee I6 4X4, still closed system. Recently the jeep was overheating, so I found a leak and replaced the upper radiator hose and flushed out the heater core. Now the engine (reading from inst. panel) won't even heat up to 210. It has only rarely gotten to 210 and that includes on the freeway (~170 on an hour drive) and around town. I still get hot air from the core. It mainly stays a little over the dash mark after 100 (~150). Also the panel temp jumps up and down, especially after giving it gas after a stop. I am thinking that it could be a bad thermostat (stuck open??) or a faulty temp sender to the panel. I thought it was supposed to run at 210.

Any thoughts or help

Thanks,

Kellen

 

[MudderChuck]

My 88 was running to cold at the beginning of winter. I replaced the thermostat and it runs closer to 200, was around 160. The OEM thermostat, has an extra air bleeder hole, built in that is supposed to help burp, trapped air, out of the system. Mine typically runs about 200, the stock thermostat is rated at 195, but they are often only accurate to plus or minus say 5 degrees (I´ve tested more than a few).
The Jeep has a low profile type thermostat, a common (Chev) thermostat will fit in the housing, but often crushes when the thermo housing is tightened (causing too cold operating temps). A stock hight thermo will only fit (kind of) in a certain position, the clearances are really hard to judge with the hoses still hooked up. The stealership thermo works best.
Trapped air in the system usually causes overheating, not over cooling. Cleaning the threads on the temp. sending unit (coolant will squirt out, don´t attemp with the engine running) at the rear of the block, drivers side top, near the valve cover and cleaning the motor to firewall ground strap (drivers side) has helped me get fairly good gauge readings.
Removing the temp. sender is helpful in removing trapped air, after a radiator or coolant system service, but can get kind of messy. Don´t remove the temp. sender with the engine running, don´t ask how I know this, coolant showers are hot and sticky.
I usually only fill the surge tank half full on a cold motor, on a hot motor the coolant expands. Over filling the surge tank, has caused my surge tank, to swell, from excess pressure. Which can´t be good for the surge tank or the system in general. Anything over about 30 PSI is apt to damage something, they usually run at about 12-15 PSI of pressure.

 

[KellenNold]

Other Hobbies?

Allright, I will try cleaning the temp sending unit and the ground stap tomorrow. Do your guys' temps vary erratically? Just on this trip, it will vary by 40 degrees and this is over like one second. Just now, the temp registered 210 (finally) at a stop and then when I gave it gas to go, it dropped to 150 right away.

 

[MudderChuck]

My temp. gauge is graduated in Celcius. It typically fluctuates between straight up (or a little left of center) to maybe an eight of the scale to the left. Or best guess between 190 and 200. I tested my thermo switch (which turns on the aux fan) it turns on (closes) at 210 or there abouts, which rarely happens.

 

[judge09]

Your instruments are not reading the actual temp of the engine correctly. There is no way the actual temperature of the engine can go from 210 degrees to 150 degrees. Time to start replacing parts.

 

[MudderChuck]

Can´t is a big word. Mine before repaires, had a pin hole leak and a stuck open thermostate. It would go from overheated (because of an air bubble) to too cold, at the blip of the gas pedal.

 

[judge09]

There is no physical way any liquid is going to drop 60 degress in a matter of a second. Esspecially in a natural environment. It CANT happen. Something is wrong with the hardware sending the signal. Start replacing parts.

 

[jay79cj7]

The gauge is measuring the temp of the fluid, not the engine... If the thermostat is stuck open, the fluid moves through the engine slowly at idle and much faster when you hit the gas. The temp could vary wildly as you stop and go and move that hot fluid away from the sender.

 

[MudderChuck]

My 88 would heat above normal at idle, a combination of a partially plugged radiator, pin hole in the radiator, that sucked air into the system, with the motor off and cooling (causeing a partial air block), a leaky surge tank and a weak fan clutch. my aux fan would turn on at around 215 or so (let me know my temp. gauge wasn´t lieing to me).
A short drive and /or a blip of the engine would send the needle down to the lower quarter of the temp. gauge. Sometimes the motor would, slip into warm up mode (high idle, a little rich), the temp. at the temp. sender for the computer, lower left of the motor, would get below 140 (let me know my gauge wasn´t lieing to me). My thermostate was hanging open intermittantly. Sometimes the motor would run at about 150, sometimes above 210, seemed to have a mind of it´s own.
New thermostat, new radiator, new surge tank, needle stays pretty much in the middle, but sometimes drops to around 190, when I give it gas, still need to get a new fan clutch.
Cleaned the grounds, the ground at the firewall, changed the normal needle position on all of my gauges a bit, seems to work better now.
Impossible is an even bigger word than can´t.