My temp gauge sits at 210 most of the time. Sometimes on the highway or around town it goes to 220-225 and stops (a/c on or off). It always comes right back down to 210-215 and has never overheated. I have replaced the radiator with a 3 row, the t-stat with a mopar one, flushed the coolant, clutch fan, coolant temp sensor on t-stat housing, and the tempeture switch on the back of the motor. The water pump is not new but it is good and pumping a good amount of water.The air has been bleed out of the system. When the temp guage is around 210-220 I used a temp gun on the motor and the temp gun never read above 195. Is their something that I'm missing or could I have a bad guage. Any suggestions??
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How Hot is too Hot
- Thread starter jt29
- Start date
JNickel101
NAXJA Forum User
- Location
- Alamogordo, NM
Replace your temp senders - one at the front and one at the rear of your block.
How do you know your water pump is pumping a "good amount of water"?
How do you know your water pump is pumping a "good amount of water"?
5-90
NAXJA Forum User
- Location
- Hammerspace
"Too hot" is about 240*F - that's when the thermostat gets wrecked and wants replacing. (If you want a better answer, take 212* and add 3* for each one pound of pressure your cap is rated for. So, with a 16# cap, you're looking at 212 + 48 = 260*F. That's the point where water will begin to boil, and steam voids will start to form. If you get steam voids in your cooling system, you've wrecked your thermostat.)
While this is still inexact, it's a better idea. Do replace your temperature sensor (the one at the rear of the head, if present, is the one that reports to the gage.)
Yes, the antifreeze is supposed to spread the freeze point and boil point of your coolant, but it's not a "perfect" solution, and the water can still boil on its own. Stay at the boiling point of basic water long enough, and you'll get a steam void behind the thermostat and wreck the thing (the wax "pill" that allows the poppet valve to open and close makes the valve stay shut. Totally.)
While this is still inexact, it's a better idea. Do replace your temperature sensor (the one at the rear of the head, if present, is the one that reports to the gage.)
Yes, the antifreeze is supposed to spread the freeze point and boil point of your coolant, but it's not a "perfect" solution, and the water can still boil on its own. Stay at the boiling point of basic water long enough, and you'll get a steam void behind the thermostat and wreck the thing (the wax "pill" that allows the poppet valve to open and close makes the valve stay shut. Totally.)
RichP
NAXJA Forum User
- Location
- Effort, Pa
My first guess is he's running a 12 or 14lb cap or the cap is bad.
Mudderoy
NAXJA Forum User
- Location
- Katy, Texas
I added a high flow 180 degree thermostat and a high flow thermostat housing. Dropped me from 210 to 190s until I get on the highway 80+ gets up to 210/215.
If you look it up they say don't go to a lower than OEM thermostat. Change at your own risk.
I'm going to switch to 3 core radiator, electric fan and later a high flow water pump. I'm trying to get the temp down to 0, lol.
If you look it up they say don't go to a lower than OEM thermostat. Change at your own risk.
I'm going to switch to 3 core radiator, electric fan and later a high flow water pump. I'm trying to get the temp down to 0, lol.
ParadiseXJ
NAXJA Forum User
- Location
- Paradise, CA 95969
muckleroy said:
two things to remember:
1.) A temp gun is measuring the temp of your engine, the gauge is measuring your coolant temp.
2.) T-stat does not control maximum temp. Changing to a lower temp t-stat will just take longer to get to operating temp.
JNickel101 said:
Thanks, for the replys. Which senders are you talking about? I have replaced the one that screws into the t-stat housing and the one on the back of the drivers side motor next to the fire wall. Is their any others?? Also the rad cap is brand new and it is a 16lbs.
Mudderoy
NAXJA Forum User
- Location
- Katy, Texas
ParadiseXJ said:
I'll take your word for #1, but #2 is what I have noticed.
The engine (coolant) will run 190's until I get on the highway. It will stay in the 190's as long as I am driving slower than highway speeds. Now I haven't seen what it will do in the 98 to 100 degree temps we have here in the Houston area.
- Location
- MilkyWay Galaxy
jt29 said:
Test the temp at the thermostat with the IR gaige and believe it. Your dash gauge or sender, the new one at the rear of the engine near the firewall is not giving good data, or you have a flow problem with trapped coolant or trapped air right at that sensor.
Use the IR gauge to look for hot spots all over the engine too! Hellofa tool!
- Location
- MilkyWay Galaxy
muckleroy said:
Houston??? Where in Houston!!!
xjrobert
NAXJA Forum User
- Location
- B.C., Canada
What's the correct cap pressure to be?
- Location
- MilkyWay Galaxy
xjrobert said:
16 PSI.
JNickel101
NAXJA Forum User
- Location
- Alamogordo, NM
I still think its your water pump....
- Location
- MilkyWay Galaxy
OK enough of the BS, wild guesses, let's try this next stuff.
Before you waist any more time and money, pull the sensor on the rear head. Take it to the kitchen stove when the ol'lady ain't around and drop the sensor end in a pot of water. Don't let the sensor touch the pan surfaces, just the water. Hook up you ohm meter probes to the sensor (you may need aligator clips on the ends of your probes) and read the resistance of the sensor and record them as you slowly raise the water temperature. At the same time use your IR thermometer (or a cooking thermometer for those of you who do not have an IRT (InFrared Thermometer) handy to read the water temperature or the sensor surface temperature.
Then go to the published data of temperature versus resitance for that sensor to see if it is working right or not!!!!
Opps, now I have done it, where is that data? If I had to guess I would say it is the same as the IAT (MAT) and the CTS, since they love to use the same parts to cut costs. Does anyone have any different data for the Gauge Temperature sensor in the head?
Here is the CTS, IAT or MAT values, again!
212 F - 185 ohms
160 F - 450 ohms
100 F - 1600 ohms
Anyway, my point is I have found that my dash gauge almost exactly matches my IR readings at the thermostat housing and the rear head where the gauge sensor is installed, there is almost no difference between the actual coolant temp and the head and thermostat temp of a warmed up engine.
He should trust his IR gauge and not the sender gauge as I have read others hear having problems even with new senders not working right for various reasons including being bad right out of the box, or having trapped air right under the sensor, etc.
I am not buying the water pump idea based on all his other data!
Before you waist any more time and money, pull the sensor on the rear head. Take it to the kitchen stove when the ol'lady ain't around and drop the sensor end in a pot of water. Don't let the sensor touch the pan surfaces, just the water. Hook up you ohm meter probes to the sensor (you may need aligator clips on the ends of your probes) and read the resistance of the sensor and record them as you slowly raise the water temperature. At the same time use your IR thermometer (or a cooking thermometer for those of you who do not have an IRT (InFrared Thermometer) handy to read the water temperature or the sensor surface temperature.
Then go to the published data of temperature versus resitance for that sensor to see if it is working right or not!!!!
Opps, now I have done it, where is that data? If I had to guess I would say it is the same as the IAT (MAT) and the CTS, since they love to use the same parts to cut costs. Does anyone have any different data for the Gauge Temperature sensor in the head?
Here is the CTS, IAT or MAT values, again!
212 F - 185 ohms
160 F - 450 ohms
100 F - 1600 ohms
Anyway, my point is I have found that my dash gauge almost exactly matches my IR readings at the thermostat housing and the rear head where the gauge sensor is installed, there is almost no difference between the actual coolant temp and the head and thermostat temp of a warmed up engine.
He should trust his IR gauge and not the sender gauge as I have read others hear having problems even with new senders not working right for various reasons including being bad right out of the box, or having trapped air right under the sensor, etc.
I am not buying the water pump idea based on all his other data!
- Location
- Southern Maryland
your temp should go down on the highway from air being forced through your radiator. if it's going up you've got a problem.
Jt29 i had a simiar problem and was about to change the water pump, fan clutch, the switch on the theromstat housing and the thermostat. It was about to rain so I did'nt want to get stuck in it so I just change the stat, gasket and added some water to the system. And that took care of the problem.
Hope this helps.
99 XJ 4.0
Ernrok
Hope this helps.
99 XJ 4.0
Ernrok
Ecomike said:
Thanks for the help I will give it a try. Also I have replaced the temp switch (the one on the back of the motor next to the fire wall) with a mopar one from the delership. And I replaced the coolant temp sensor (the one on the t-stat housing) with one from autozone. Do you think that could play apart in it, maybe their is a difference in the elec. connection or ohms sending a bad single to the gauge or computer. Also I replaced these before I replaced the raditor could the temp got to hot messing up the sensors?
gbyrnes
NAXJA Forum User
- Location
- Albuquerque, NM and Tempe, AZ
Re: How Hot is too Hot (or Cold)?
Hi, I've been having a related problem with my temp. I found a couple earlier threads on it, but they haven't answered definitively my problem.
When i am idling, my dash gage reads around 200+-10. But, when i get to speeds of 50 and up, my temp starts dropping over a couple minutes to about 160+-10. This is happening in ambient temps of 50 to 90 degrees. The problem also seems to have started when I replaced the speed sensor on the transfer case. I know that this sensor helps control idle, can it have any impact on the cooling system? And if so, why would replacing a dead sensor with a live one start problems with lower temp readings than I'd want?
I have noticed a considerable drop in gas milage. I'm running a 92 with the HO 4.0L. I've seen many things suggested, but I'd like to narrow things down.
I think I should check the thermostat, but should I also check the sender unit? The gage itself for possible voltage problems? Some other miscellaneous part?
Thanks
Hi, I've been having a related problem with my temp. I found a couple earlier threads on it, but they haven't answered definitively my problem.
When i am idling, my dash gage reads around 200+-10. But, when i get to speeds of 50 and up, my temp starts dropping over a couple minutes to about 160+-10. This is happening in ambient temps of 50 to 90 degrees. The problem also seems to have started when I replaced the speed sensor on the transfer case. I know that this sensor helps control idle, can it have any impact on the cooling system? And if so, why would replacing a dead sensor with a live one start problems with lower temp readings than I'd want?
I have noticed a considerable drop in gas milage. I'm running a 92 with the HO 4.0L. I've seen many things suggested, but I'd like to narrow things down.
I think I should check the thermostat, but should I also check the sender unit? The gage itself for possible voltage problems? Some other miscellaneous part?
Thanks