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Discussion Starter · #1 ·
All of a sudden out of the blue, with no warning, the engine went hot. I was able to pull over immediately, the only reason I noticed, was because AC stopped cooling, could hardly see the warning indicator. I had a friend that was meeting me pop the hood. Nothing seemed out of ordinary. No smoke, leaks, noises, fans were spinning and when the car was turned back on it was basically back to normal temp...I had it towed, didnt drive it. The mechanics, could NOT, I repeat could NOT get the issue to replicate. They decide it was a sensor/thermos issue and replaced them. I took the car home the next day and had no issues for a week. The next weekend, I was on the road for about 45 minutes when I noticed the temp gauge start fluctuating wildly from almost hot to way below normal to normal and so on. The temp never went to hot nor did the warning light come on. I was on the interstate in the middle of nowhere, two hours from home. I phoned some friends who were about 45 mins behind me on the road and they suggested I keep moving unless the gauge starts staying above normal. It never did. I decided to turn AC off and see if that would help, thinking that may be causing extra engine heat, it actually did suppress the issue for about 30 minutes, it wasn't until I was sitting idle waiting for garage to open, AC still off that the gauge started fluctuating again. Car stayed in garage overnight, then drove the car, 25 mins away, the next day, back to mechanics and never had a fluctuation issue during drive. The car stayed at mechanics shop for 3 days while they checked engine and tried to get system to replicate. On day 3, after driving for over an hour at various speeds, really working the RPM's it started fluctuating but never overheated, just fluctuated. This was when they decided to do a block test and it came back negative the first time, the second time they said maybe there was an issue but didn't have conclusive evidence to prove so... they literally were so perplexed they told me to come get the car and sell it. I decided to get a 2nd opinion and took the car to a respected mechanic in the area who works on my families cars quite a bit, he has had the car two days and has been unable to get the car to replicate. He also checked engine block and found no issues, definitively, in his testing. i'll note that, the random fluctuating began when I pulled out of a gas station, onto the freeway on ramp and really had to gun it to get up to speed All other systems in car are working fine. This came out of nowhere. There were no prior signs of problems. No weird noises. No smoke. No leaks. The AC works fine, haven't tested the heater as its midsummer in Texas and HAH. The car has been babied with regards to maintenance. The last little tidbit of info.... I swear I watched the temp gauge fade in and out when it was fluctuating but neither mechanic got that to replicate either.
I've read forum after forum, recall sites, etc. Similar issues are being discussed....Many of us had replaced mutliple parts and spent thousands of dollars only to still have the issue. The most frustrated of frustrated consumers after replacing sensor/thermostats, radiators, water pumps, flushing coolant system, burping system for sometimes days, resetting temperatures, testing the engine blocks have discovered that adding ground wires, digging into dash cluster issues and messing with radiator harnesses have fixed the issue. It just seems to me that these kind of issues would have existed from the get. I'm so frustrated and don't want to get rid of a 6 year old car simply because no one can figure it out. ANYONE ELSE DEALING WITH THIS....?
 

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I have seen where a lot of air in the cooling system cause this. The air will not be the same temp as the coolant. If there is too much air then it can settle around the sensor and after a while the coolant boils back up to cover the sensor and the temp quickly rises.

I would open the radiator when the engine us dead cold and see if it is 100% full. If it is not then there is a minor leak on cool down causing lack of vacuum to pull coolant back into the system from the overflow or a bad radiator cap which would do the same thing.

And Hyundai coolant gauges are worthless for anything other it's cold, OK or too late.
 

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Discussion Starter · #4 ·
Interesting follow up to my story. I decided after letting mechanic keep car over weekend and run more tests Monday to go and pick up my car on Tuesday. My plan was to drive the heck out of it for as long as it took to try and get the gauge to fluctuate. When I went to start the car, the battery was dead. The battery is only 14 months old, we replaced the battery and I drove the heck out of the car for a day and then the next day ---- temps are over 100 degrees in Houston right now ---- and nothing so far. No overheat, no fluctuation, nada. I have noticed the car still doesn't want to turn over as quickly as it did immediately following the battery replacement.

Could my issue be battery related?
Is it possible the battery didn't allow a fan to turn on causing car to overheat, once?
And then fix itself until a week later when with returning outside heat and long term driving cause the temp gauge to just start fluctuating because battery was supplying enough electricity to the car?
I suppose my car could have an electrical issue that is causing the batteries to go bad early.

So frustrated.
 

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A bad electrical supply problem could cause gauge issues. I don't know if your car has the electric t-stat? I don't think it does.

But the gague is woefully equiped to tell you the temperature of the engine. You really need an OBDII reader to see what the Engine Coolant Temperature sensor is reporting.
 

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Discussion Starter · #6 ·
Neither mechanic got error codes on the OBD readings. Is ODBll different than what they are doing?
 

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Yes it gives you real time temperature data as well as many other real time numbers. They also read and clear codes.
 
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