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Overheated but not showing it


KingCarGuyZ

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Ok, so was idleing the Jeep for A/C on a hot day, and was watching the gauge, nothing. Stayed right above 210 where it normally is. The I turned her off went inside, and when I came out to start her, she was missing like all hell and backfired a few times, wayyy rich. In that second the coolant gauge pegged. I immediately turned her off. I then cycled the ignition and the coolant gauge was right back to normal so I tired to start her, again with the missing. Killed the engine and plugged in my code reader, lo and behold ECT of 250 ahhh! I recently replaced the coolant temp sensor (one on the top of the engine) and when popping the hood the radiator is HOT. Even by jeep standards. While I sit here letting her cool down, I’m wondering what happened and why didint my dash inform me sooner? Ideas?

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KingCarGuyZ

KingCarGuyZ

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Also worth noting that this idiot tried to start her 2 more times before pulling out the reader, figuring what my temp really was and clearing the code (P0420 that I’m working in that I believe to be un related) that was the only code
 

pagrey

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Unfortunately the gauge has a filter to keep it from going haywire and smooth it out. Sounds like you might have steam pockets causing wild fluctuations in temperature at the sender that the computer was trying to filter that out. In your case probably doing more harm than help.
 
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Chris

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Is the radiator completely full? Same thing happened to me and it turns out my radiator was not entirely full, thus creating air pockets.
 
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KingCarGuyZ

KingCarGuyZ

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Up-date made it home running 214-225 whole way, I’ll have to “burp” the radiator latter today or tomorrow after she’s cooled down. The coolant overflow tank was past the full mark, but not near actually overflowing.

I wonder why the gauge didint show while the Jeep was cooling down from the 250? Took 10-15 min and the gauge didint move at all.

also I opp temp on these really 210-220? Seems kinda short jog from 220- the 250 of aw hell she won’t run right.
 
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KingCarGuyZ

KingCarGuyZ

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Also did some reading on other threads and some people mentioned smelling coolant while driving. I used to smell that but it’s petered out as the weather Got hotter, supports the leak with air pockets theory.
 

pagrey

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Possible your new sensor is bad, wouldn't be the first time a new sensor wasn't any good. I'd replace the radiator cap for fun, it's always a good first step with all cooling system problems and isn't too expensive.
 
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KingCarGuyZ

KingCarGuyZ

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I thought the sensor was bad, but that wouldn’t explain why I’m getting an accurate reading from the OBD2 reader live data, if the sensor was bad I would think it would feed the computer bad info thus not letting me know that the Jeeps was overheating at all. Not feed the gauge junk but the computer the truth, seems like air pockets is more likely especially with how much it was jumping around on the trip home. Something to keep in mind though.
 
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KingCarGuyZ

KingCarGuyZ

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Appreciate all the quick responses, means a lot when you could be stuck on the side of the road.
 

LONGJP2

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IIRC, the gauge actually only shows low, normal, and high. So that might be why you didn't see it moving as it heated or cooled.
 

Jerry Bransford

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That your overflow tank is past the full mark might mean your radiator cap is either not tightened all the way down or perhaps it's bad, or maybe someone installed the wrong pressure cap... it needs to have an 18 lb. pressure rating.
 
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KingCarGuyZ

KingCarGuyZ

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Gotcha, gonna go ahead and order a new one, any reason I need to go Mopar or will any 18lb cap work?
 
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KingCarGuyZ

KingCarGuyZ

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Stant is 5 bucks from amazon, autozone wants 30 for there’s. Guess that’s the price you pay to get it now.
 

mrblaine

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Gotcha, gonna go ahead and order a new one, any reason I need to go Mopar or will any 18lb cap work?
If it were mine I would do a drive around flush, pull the thermostat after the flush. Flush with tap water until clear, one more time with distilled, and then install a new Mopar thermostat with a 1/8" hole drilled next to the jiggler. I would fill it with Mopar coolant since that has always worked and call it good. I suspect that will solve most if not all of your problems.
 
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KingCarGuyZ

KingCarGuyZ

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Tried burping it, nothing. So I installed a new thermostat with the 1/8th hole. (Stant I believe) that dropped the temps when drivibg 40-50ish a little, but I’m still at 225 and when is stop it quickly climbs to 240 even at a light. After seeing the inside of the block I think I’m going to do a coolant flush and a fan clutch next.

Any way to “upgrade” your fan? I know I probably don’t need it, but in my mind more air is more better. Heard something about old Ford Explorer 9 blade fans and I think I remember reading something on here about a AC Delco 6 blade fan that pulled significantly more air than stock.

any reason I need to go MOPAR for fan clutch? Or will A decent aftermarket be good?
 

pagrey

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Forget fan upgrades, I don't think it's worth the effort. The aftermarket fan clutches seem to flow more air in my experience, specifically the hayden, I think it's a good choice.
 
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KingCarGuyZ

KingCarGuyZ

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Ok got the Hayden clutch in it’s way from amazon, like 40 bucks. I think that will help a lot, though part of me is tempted to by pass the clutch all together and jut have the fan spinning when the engine is on, this being TX and all.
m

I got a bunch of diff quotes for a coolant flush, I have a 110dollar 20 min flush, basically a drain run cleaner through it once and fill, and I have a 190 3 hour flush that’s drain, push chem cleaners through a bunch, distilled water , then fill. I’m guessing it’s worth the extra $$, what do y’all think?