Hey, I am a fairly new tj owner (1 month). When I bought my 2000 Tj Sahara, it came with no thermostat because the previous owners decied they didn't need it in texas. I installed a motorad 195F thermostat and thermostat housing with a new temp sensor (old one was siezed in the old housing) since I was taking my jeep with me up to school in michigan. In texas the jeep ran fine at it's opperating temp of 210F after the thermostat install (70F outside temp in average), and even on a 45 degree morning. On my drive up to michigan last week though, somewhere passed indianapolis, as I entered colder air, my engine temp droped to 185F (in the span of like 5-10 min by the way). Now having been at shcool for a week no matter what I do the engine will not heat passed 185F. Idling, highway speeds, doesn't matter. I thought maybe the thermostat I had jsut put in went bad, so today I put in a new 195F thermostat and tested the old one. The old one fucntions perfectly and the new one didn't fix the issue. I am really confused what the issue is here. Maybe the thermostat is properly installed and coolant is still making it passed when it's closed? I really dont know. maybe it's something else like a fan issue but I think my fan is fine (im not really used to mechanical fans so I don't know). I used an OBDII reader to ensure that the ECT sender matched. the engine temp read by the ECU and it does. So the engine is in fact at 185F. If all else fails my final resort will be to cover the radiator partially with cardboard to limit airflow, because I'd like to use my heater. Thank you to anyone who can help.
TJ running below operating temp in winter
- Thread starter alejad
- Start date
Poor quality thermostat that's not working at the 195 temperature.
I went through several until I bought a Robert Shaw thermostat sourced from Flowkooler.
-Mac
I went through several until I bought a Robert Shaw thermostat sourced from Flowkooler.
-Mac
My guess is your new temp sender went bad. That's the only sensor to measure water temperature, and is what the ECU uses whether read by the dash gauge or an OBD reader. The OBD reader just confirms the dash gauge is working correctly.
If I am not mistaken, becuase I have a 2000 TJ 4.0 it still uses two seperate sensors like the YJ. My understanding is that the swtich to a single ECT sensor happened in 2001. What i'll do is double check in the engine bay this evening and look for the engine block side ECT sensor where it would be if I had it to confirm. If I in fact I don't have one in the block, like you say, I will go ahead and give replacing the thermostat housing sensor a shot. Thanks for the help.
Thanks, I just ordered a mopar one to see if it fixes the issue. Cant hurt when compared to the cheap $6 motorad thermostats I had tried to put in the car. Im just a little skepticall that both of the previous new thermostats weren't working properly. Maybe there is some weird heat transfer shenanigans going on and the cheaper thermostats can't handle it, becuase I tested the first one after the issue came up with my stove, some water, and a thermometer and it opened at exactly 195F. Thanks!
Oh, great! well then we'll see but I guess it might not make a difference. Thank you!
Verify the fan clutch is not locked up. If it is, it will roar, suck HP, and overcool the engine.
Engine cold it should turn. Run it until it's up to temp. Stop the vehicle, shut off the engine and the fan should be locked up.
-Mac
-Mac
If the clutch is completely locked up (failed), you won't be able to turn it by hand either hot or cold.
Even when hot, you should be able to turn it, but with considerably more resistance than cold.
Even when hot, you should be able to turn it, but with considerably more resistance than cold.
Ok so it is not locked up. It turns freely with the engine off. Thanks.
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When it's hot the clutch locks and the water pump spins the fan cooling the Jeep by drawing air through the radiator. There's still going to be some slip.
-Mac
-Mac
I just checked and it spins freely with the engine off. So I believe that means not locked up. Thank you.
The resources section has a parts list for 2000 TJ and it shows only one ECT sensor Qty 1 in 4.0L. There is likely an FSM in there as well for 2000.
I agree that the ECT sensor is suspect here if the thermostat was tested to open accurately at ~195F while the ECT showed 180. And it is something you want to try to resolve as the ECT reading too low can result in the PCM staying in warm up timing and fuel tables, negatively affecting performance. But it is also possible that with the heater running full blast in the vehicle you're pulling enough heat out of the engine that it actually is dropping to 180F.
If you have access to an IR thermometer, you should be able to get a good reading off the thermostat housing where the ECT sensor threads in or heater line comes out and feel the upper hose get hot when it hits 195F with a little allowance for the thermal mass of the thermostat housing. Be aware there is typically a small bleed port in the collar of the thermostat which will allow some hot water to pass before the thermostat fully opens and you will start to feel the upper hose warm before it rapidly changes temp.
I believe the lower outside temps are also affecting your radiator efficiency as well. Assuming the system is fully burped and operating correctly. I've logged my radiator consistently open at 194F indicated and then while driving on the highway drop to about 190F and stay there with the thermostat at least partially open this winter.
I agree that the ECT sensor is suspect here if the thermostat was tested to open accurately at ~195F while the ECT showed 180. And it is something you want to try to resolve as the ECT reading too low can result in the PCM staying in warm up timing and fuel tables, negatively affecting performance. But it is also possible that with the heater running full blast in the vehicle you're pulling enough heat out of the engine that it actually is dropping to 180F.
If you have access to an IR thermometer, you should be able to get a good reading off the thermostat housing where the ECT sensor threads in or heater line comes out and feel the upper hose get hot when it hits 195F with a little allowance for the thermal mass of the thermostat housing. Be aware there is typically a small bleed port in the collar of the thermostat which will allow some hot water to pass before the thermostat fully opens and you will start to feel the upper hose warm before it rapidly changes temp.
I believe the lower outside temps are also affecting your radiator efficiency as well. Assuming the system is fully burped and operating correctly. I've logged my radiator consistently open at 194F indicated and then while driving on the highway drop to about 190F and stay there with the thermostat at least partially open this winter.
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