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Discussion Starter #1
Hello everyone! Have not posted in several years thanks to a near perfect Elantra. My 2010 started illuminating intermittently the high temp light last November, no codes, apparent normal running engine temp. and normal heater output. I changed the radiator sending sensor and coolant antifreeze, 11/30/2017 and no more warnings, until yesterday afternoon after a short ride (7 miles) again apparent normal engine compartment temp. normal hot heater output. What should I test next?
 

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Discussion Starter #3
Just an idiot light... I thought that if the thermostat was sticking closed I would not have hot heater output.
 

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Just an idiot light... I thought that if the thermostat was sticking closed I would not have hot heater output.
Depends on failure mode. If stuck partially open you will get plenty of heat from the heater because the engine is not getting enough cooling capacity. Even if stuck wide open you will get heat unless outside temps are very cold.

I cannot stress enough to check the thermostat. This is a known issue with these 2.0L engines, and that cooling system is excellent if all is in working order, but has no capacity for any failures. As you may have noted when you changed the coolant, there isn't a lot of fluid in the system. It will keep the engine warm in the winter, and even cool in Texas summer heat, but there is no significant excess capacity in the design.
 

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Discussion Starter #5
Good points! I will change the thermostat the car has 70500 miles already. The cooling fluid was very clean when changes last November, and what I can see inside the radiator looks good today. So I hope no damage has been done!
 

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Discussion Starter #7
I drove about 7 miles to the dentist, no warning light. spent about an hour there, came out to drive back home (outside temp. 93 degrees, parked partially under the sun} started the car and about 2 or 3 minutes the warning light came on [flashing!] so pulled into the driveway back, shut it off and went to check under the hood. Notice the fan stopped as soon as I turned the switch off, other than that nothing extraordinay that could see. After quite some time re-started no lights, drove home with A.C. turned off, heater on, windows open. O.K. so far, but I think this issue should be addressed, this car always has had a very "lazy" fan, I mean it takes time to turn on and almost always turns off as soon as you shut the engine off, as opposed to other 4 cyl cars i have owned. [ by the way I started the radiator with pigtails from the battery and runs fine.
 

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Elantra (XD & HD & Touring) with 2.0L through all yrs is horrible for cooling system,, Leaks, radiator tank splits, Upper hose dribble onto hose below it (see white-green dry chalk like stains).... Thermostat almost maintanance item..
 

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If that light is coming on the temp is really high. Over 230F I bet. Could be a bad sensor but you need to see what the actual temp of the coolant is.


With an OBDII reader if the sensor is bad it will show up when all is cooled down to ambient. Then see if it agrees with the actual air temp.


I have an OBDII reader and gauges on my Gen Coupe. One thing I do before starting is turn on the key and see how the oil, coolant, IAT and ambient temps sensors all read. They usually are 1F within each other. This may vary if the car sits in the sun or there has been a large temp change with the air during the day.
 

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Discussion Starter #10 (Edited)
Red, can you tell what model of OBD2 reader you use? I tried to remove the thermostat to boil it and test it, but I can't figure out how to do it. The videos on you tube only show replacements of older generations elantras, in which case it's a very easy job of just replacing 2 bolts that secure the housing to the upper hose. I don't want to have to drive a long distance to the hyundai dealer, like 50 miles, if I can figure out what's wrong with the car. Thanks in advance.
 

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this car always has had a very "lazy" fan, I mean it takes time to turn on and almost always turns off as soon as you shut the engine off, as opposed to other 4 cyl cars i have owned. [ by the way I started the radiator with pigtails from the battery and runs fine.

I was wondering if maybe the fan wasn't turning on. Maybe next time the light starts flashing, look to see if the fan is running.
 

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I have two. One is my smart phone and the Torque app, it requires an ELM bluethooth adapter. On my Accent I have an old Ultra Gauge connected all the time.


The ELMs can be had cheap ($10 and up) but some are better than the rest so beware low prices. The Torque app is $5 and $5 for the Hyundai EX plugin for it.
 

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Elantra (XD & HD & Touring) with 2.0L through all yrs is horrible for cooling system,, Leaks, radiator tank splits, Upper hose dribble onto hose below it (see white-green dry chalk like stains).... Thermostat almost maintanance item..

Ditto. Daughters 2006 was watched like a hawk. Never any problems, but stayed on top of level checks, coolant drain/refills.

OH! Check the radiator cap and make sure BOTH seals are good. One is backed by the spring and sets the pressure limit before feeding the overflow tank, the other rests on the lip of the radiator and seals for vacuum to draw the fluid back from the overflow when cooling. The 2006 kept filling the overflow, but not drawing back. That's how I found the bad radiator cap.
 

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Discussion Starter #15
I will have to go with something like the "ultra gauge" since I'm an old computer ignorant senior that doesn't even have a smart phone. Last Nov. i suspected the fan sensor unit by the thermostat was defective, Autozone checked the obd2 and it showed that was the case, they said. I replaced that sending sensor plug, then waited for the car to get hot, idling, and the fan started; though it turned off as soon as I turned the ignition off, thas always the case with this car since new, I dont remember ever hearing that fan running after parking the car when hot, like other cars I have owned.
 

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Discussion Starter #17
Problem solved! The second fan sensor that I had replaced last Nov. turned out to be bad too. Tested it on the kitchen stove in boiling water, it never closed the circuit. Got another and tested it to about 190 degrees and it did. The car runs great. Thanks for all the responses, I'm planning to get an Ultra Gauge scanner and leave it connected to Temp. gauge. Don't trust idiot lights (or "new" heat sensors) anymore...
 
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