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Old 10-09-2009, 10:33 PM   #1
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Engine running too cold???

Today my 2.5, 90 YJ's temp gauge slowly started dropping from it's normal 205'ish down to about 100. Is this normal? It seems awfully low. I had just checked the fluid in my rad bottle right before this happened and it was almost empty, but the radiator was full, i filled the bottle up. I was about a mile from house when the temp dropped. I got home, shut the Jeep off & started it back up, a few times, it seemed to be idling really rough, and around about 700-800 rpms & acted like it wanted to die (normally idles at about 1000 rpms) Would the rough/low idle have anything to do with the drop in temp? I do know that my heater does not work very well (or maybe that's all the better it's supose to work) on a 45 degree day, it DOESN'T keep me warm at all. I'm wondering if this could be the thermostat? The Jeep seemed to be idling oddly when i left earlier today & a few days ago, i thought i faintly smelled antifreeze. I'm not sure what this could be, or if the temp & idle have anything to do with each other.

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Old 10-09-2009, 10:46 PM   #2
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I wouldn't say its normal no. Doesn't the gauge start at 100? Normal is roughly middle of the gauge 205-210. Usually if its a stuck open thermostat it would take forever to heat up or stuck closed it would overheat.

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Old 10-09-2009, 10:48 PM   #3
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Nope I've had more problems before this & no check engine light. I'm guessing someone busted it out. Is it dangerous to drive like that? I mean, is it going to hurt anything?
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Old 10-09-2009, 11:30 PM   #4
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I would probally try an fix it as soon as possible. I'd see if it was still acting the same way the next time you drive it.
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Old 10-09-2009, 11:44 PM   #5
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No. The gauge starts at 0. I probably drive I'd say a mile or a mile in a half before it warms up. Yea mine has always ran in that temp range until today. That's exactly what I'm gonna do. Drive it tomorrow and see if it still does it. One day it does something then it never does it again. Haha
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Old 10-10-2009, 12:52 AM   #6
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not sure but someone told me a thermo stuck open will kill your piston rings. cuz it messes with the op temp of the rings. on that note
I would get it checked out asap.
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Old 10-10-2009, 02:05 AM   #7
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yepper, too cool will not allow fuel to atomize correctly. too wet, washes the cylinder and causes excessive wear. heat is good!
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Old 10-10-2009, 09:03 AM   #8
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Thanks guys. I'll def get that fixed asap. Hopefully it doesn't do it the next time I drive it!
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Old 10-10-2009, 02:07 PM   #9
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It does sound like the thermostat, may be stuck in the open position. They go bad, with time.
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Old 09-14-2010, 06:23 PM   #10
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Cool Enginge Running Cold

The engine temp. gauge in my YJ went from a normal 200 to a lower than normal 120 while I was crawling down a high mtn pass near my home in Colorado last Friday. After feeling all the coolant hoses and finding out they were all plenty warm, including the inlet and outlet to the heater core, I was at a loss as to what might have caused this. Well of course I read plenty of JF posts and decided to try the simple method of checking the temp gauge. It checked out fine, but I noticed the connection was loose. After crimping it a little and snugging it up to the temp sending unit my gauge read 200!! This all took ten seconds and goes into the record books as the cheapest and fastest fix on my Jeep ever.
Yours sounds more involved though because you have no heat in the cabin and I did. Start with the inexpensive stuff like changing the thermostat (buy the 195 degree one). I'll bet that fixes it. If that doesn't work consider whether or not your heater core is clogged. This item is buried under your dash and a radiator repair garage could change it for around 300 bucks if you can't change it yourself
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Old 09-17-2010, 08:18 PM   #11
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Yeah mine usually runs, like you guys said, about 205-210, then sometimes it'll drop all the way to like 160-170 or so, then normalize again. I'm assuming this is probably normal, as the thermostat will open and close as needed. My last car was a Honda (forgive me lol), and I was used to the temp gauge staying put all the time at operating temp.
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Old 09-17-2010, 09:49 PM   #12
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Make sure you dont have air in the system or the sending unit needs to fluid level to read correctly.
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Old 09-17-2010, 11:26 PM   #13
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Sensor or thermo, been there. Be grateful it's a cheap fix!

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