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Erratic Overheating in my 2010 Hyundai Sonata
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cahm8791
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Aug 26, 2019, 7:48 AM
Post #1 of 20
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Erratic Overheating in my 2010 Hyundai Sonata
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My Sonata has been both wonderful and a terror at the same time. When I purchased it from a local dealership, it seemed strong and reliable, even at 120,000. Then I had a trouble code pop up and about the same time, I realized that my car's temp was super low and stayed low. The trouble light basically said thermostat trouble. So, I replaced it. The trouble light disappeared and the temp stayed at NOT (Normal Operating Temperature). One day, while at a drive thru, the terror started. The temperature all the sudden started climbing. I would turn off the car and restart the rest of the time there and then while driving, it cooled off, but would climb as soon as we had to stop at a light. I checked fluids which were all normal. I checked for any discoloration in the oil to see if there were any signs of coolant from a head gasket issue. Did not see anything concerning. What I did find out quickly is the fan would not automatically turn on. It only came on when I turned on the AC, so not a relay or bad fan necessarily. That was all at the beginning. Ever since, the temperature issue has been extremely erratic. I can travel to work or the kids school and have no issues, then the next day, it overheats quickly. Then some days, it stays normal for a long time and I will look at the gauge where it says NOT and look down a second later and it's almost at maximum. I will put the heater at full blast and within 90 seconds it at NOT. The problem is occasionally, even that doesn't help. With the heater on, the temp goes up but cools down while idling. I'm at a loss of what is happening. I think of small things like air in the coolant system, coolant temperature sensor issues, etc. But things are so unpredictable. Anyone had similar issues or ideas?
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Tom Greenleaf
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Aug 26, 2019, 8:40 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Overheating, heater erratic, temps all over the place all point to vapor in the cooling system despite a reservoir saying it's correct. If it can't control pressure and vacuum when cooling down it's sucking air in not coolant back.
Sensors don't accurately read vapor or fast enough and here you are.
This IMO needs all checks for head gasket, and anything allowing cooling system to stay full, hold pressure and since OFF time is cooling down slight vacuum to pull back coolant and isn't doing that.
That first before it's "game over" for this engine not much tolerates excessive heat.
BTW when heater can't blow warm air at you and engine should be warm enough it's almost certain it hot vapor doesn't exchange to warmer air output of a heater LIQUID does. That's the strong clue.
No you may NOT see where it's going or lost especially if burning it may also be intermittent when it does if so.
Lots to check and I suggest not waiting to save this,
T
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Hammer Time
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Aug 26, 2019, 8:47 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Your first comment stated it overheated at idle. That points directly to a fan problem.
The fluctuations you described due point to air pockets in the system as Tom pointed out. They could have been there since the thermostat job or it could be a blown head gasket. That is yet to be determined.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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cahm8791
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Aug 26, 2019, 8:56 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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I appreciate the response. It's definitely a concern. The heater works 100%. It is always hot. Not sure if that changes diagnostics. Would there be any other things I could look out for to help diagnose? If it is a head gasket, I would just junk it. It's not worth the $2500+ price tag. My thinking is could it be the hose or thermostat housing is not on good enough from the thermostat replacement?
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Hammer Time
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Aug 26, 2019, 9:05 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Pressure test the system to find any leaks and repair them. Then get all the air out of the system.
We use a vacuum fill tool to accomplish this. You may be able to rent/borrow one from Autozone. The coolant must be room temp to do this though.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
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Aug 26, 2019, 9:15 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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I do think the Zone rents pressure testers. Just learn how to use that one and how to release pressure if running this many would allow pressure over the limits as it warms up.
One note is pressure is from expansion of coolant the pressure cap and integrity of system allows coolant to expand, make pressure to about 15lb rating of cap which raises boiling points so coolant stays liquid not vapor. It has to stay liquid just know that. Not holding pressure for any reason it would boil = vapor,
T
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Hammer Time
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Aug 26, 2019, 9:21 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Don't run the engine withy the pressure tester attached. That is dangerous.
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cahm8791
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Aug 26, 2019, 9:41 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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All right. Thanks for the tips everyone. My fear is head gasket from the first time it got hot when the fan probably stopped working. I know a little about cars, but not enough to do a pressure test on my own. I will take it to my mechanic and have him do it.
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Hammer Time
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Aug 26, 2019, 11:14 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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The pressure test will find leaks if done correctly but likely won't help with head gasket diagnosis. That can be very hard to confirm, even with chemical tests.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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cahm8791
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Aug 30, 2019, 7:38 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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*Update*
I have an appointment with my mechanic next week, but this morning on my way to work, it did something unusual. When I started the car, the needle climbed rapidly to NOT (normal operating temp) literally 2-3 minutes of neighborhood driving. Then about 7 minutes later while on a busier road, the needle in less than 2 seconds shot from NOT to maximum temp. No creeping up or anything. I cranked on my heater to full blast and pulled over trying to give it time to cool off. I got out and opened the hood and felt little heat radiating off the engine. I expected rolls of heat to be coming off. The top hose was hot and the other one below was cold. Anyways, I started the car and the needle was at the maximum still but I only had about 2 miles to go. With the heater still on full, I started driving and in less than 30 seconds, the engine temp quickly returned to NOT and stayed that way the rest of the trip. Does this point to anything different?
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Tom Greenleaf
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Aug 30, 2019, 8:03 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Of course that's too fast to really be that hot. IDK, either air, even exhaust air (super hot) hits a sensor or sensor wrong. Hose was hot at 7 min? Bit soon. Did the heater work - said that was a strong clue of air.
Back to not suggested pressure testing and testers: 1st you are sending it out so let them deal with it but I'll explain why it's info to leave one on while engine is running.
This is what I suspect for now. Starting from cold with pressure tester attached or not but quick to go put it on - RUNNING - not safe nor for the timid so no suggested.
Why do that? From cold, metal, coolant and all the pressure is from expansion by heat normally the liquid of coolant. If it shoots right up in sometimes 30 seconds is exhaust gasses invading the system! What else? Not much else would do that. You have to be quick to release that. Now zero again but can't be really hot put it back on AYOR could be burned. All within a couple minutes. It started again from zero you had no cap on it if it spikes again the problem is more clear is why.
Beat on it DON'T do that it's dangerous and risky. On the other hand it's lots of info.
Now question is whether you should drive it or not anymore or if damage already it would ruin any chances of a fix for the budget allowed you said not much.
Reason I think it can stabilize is when moving liquid can reach around finally thermostat finally works somewhat properly and just maybe if an exhaust invasion it could be sealing from heat?
It's hard to diagnose and be sure but all starts with knowing it's truly full of coolant to begin with this isn't so easy to do already discussed.
Right move IMO let the pros diagnose it there is some danger never mind the costs getting hurt isn't good ever. At least then you can decide what to do.
There is some room to not know exactly unless there a go ahead for a fix to really see the fault(s) and know it's more than could possibly be seen is a real chance.
Good luck. Have a nice weekend I hope wherever you are just don't get hurt with this thing or make it worse,
T
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Hammer Time
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Aug 30, 2019, 8:12 AM
Post #12 of 20
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Sounds like you have lost a lot of coolant and the system is full of air. Don't drive it that way or you will be buying an engine soon.
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cahm8791
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Aug 30, 2019, 8:16 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Yes, the total running time had been roughly 12 minutes when the gauge suddenly spiked to maximum. The hose was hot, but not to the point of "ouch". The heater started by blowing cooler air but very quickly blew hot air that a normal running car does. The heater stayed hot the whole trip. My unprofessional guess from everyones input and symptoms is somehow a mixture of A. air in the system and B. Cooling fan not coming on automatically. If air is getting in, the mechanic and I can quickly figure out where from and if it's repairable.
Oh, and I still have full fluids and do not see any weeping or moisture of any kind on the engine block or anywhere.
I will update my thread as I learn what it is diagnosed with.
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Tom Greenleaf
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Aug 30, 2019, 9:15 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Reservoir doesn't really count. It's AIR +/or vapor (steam = vapor) inside and unseen. Stay safe the stuff can cause 3rd degree burns - not worth that BUT can't exchange heat for engines,
T
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Hammer Time
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Aug 30, 2019, 9:27 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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Yes, if you have a leak in the system the engine will draw in air when it cools down rather than draw from the reservoir.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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cahm8791
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Sep 7, 2019, 6:12 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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**UPDATE**
My mechanic finally got to look at the car, he diagnosed a couple problems. One he fixed and one that will have to be fixed soon.
The coolant sensor was the culprit. It was sending bad signals and not controlling the fans properly. Once he replaced it, he nor I have had any temperature issues so far.
The other problem he is seeing is oil is leaking into the engine from the valve gasket or the valve stem orings. (He didn't disassemble it to find out which) A little expensive, but something doable in the near future, just have to watch the oil levels extremely closely.
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cahm8791
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Sep 7, 2019, 7:00 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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No, the problem is not the gasket now that you tell me the difference. I just couldn't remember which one the mechanic explained to me until you did, but smoke blows out of the exhaust for a little bit after starting the car so we know it's burning oil which he had said valve orings. That misinformation on my last post is my fault and my bad listening/memory lol.
Either way, my wife and I have had enough with the problems that keep coming up and question if a car with this many miles and constant arising problems is worth it. Maybe sell it as a mechanics special. Definitely won't get back what we bought it for.
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Hammer Time
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Sep 7, 2019, 7:13 AM
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Re: Erratic Overheating in my 2010 Hyundai Sonata
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That is probably a smart decision given the facts and symptoms.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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