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Hyundai 2005 sonata overheating

Myu 2005 Sonata overheats when stuck in

beltway traffic.(always) Cools down if turned off, or I run the HEATER (even in summer…awful). Has also overheated at 60MPH on freeway, driving up a short hill

(sometimes), at first stop light after exit

beltway. Randomly and usually in hot humid

weather. Dealer did SUPER (expensive) FLUSH but performed NO OTHERTESTS because

it wasn’t overheating the day he had it.

The manual says if car overheats get towed

to a dealer because it could be a coolant

leak (internal). Other suggestions have

been radiator? thermostat? fan? sensor?

Anyone else have this problem? I found

similar problems on the internet with

Hyundais, but my car is under warranty

with Hyundai for 8K more miles or end of year.?? HELP

Stick with the manual; don’t drive it anyfurther. You could have a stuck thermostat or a clogged radiator. The fact that you need the heater, which is a small radiator, to cool things down indicates that the radiator may not be doing its job. The dealer has to do a number of tests. Carefully document all the symptoms, just as you would going to your doctor.

Since the car is still under warranty, and Hyundai has a generally good warranty, let the dealer fix it properly. If you go to a private shop you will have trouble collecting from Huyndai.

Good luck.

Hi thanks for your response BUT the DEALER is the pain in the ass. Unless I can
stop everything I am doing WHEN the car overheats (usually cant…have customers in
my car, etc and am on the beltway, etc) they say they cant do anything because THEY
cannot duplicate the problem. Because it IS random. I mentioned the manual saying
to bring it in immediately and they said that’s what I would have to do to get them
to TEST for ANYTHING at all wrong with the entire system.

The biggest issue is that I know it WILL overheat in stop and go beltway traffic,
but when I am in that situation, I usually cannot tow the car immediately and if
the weather is cooler the next day, it wont happen.

I am very frustrated with the warranty which will cover any of the problems it COULD
be…but only if the dealer will BELIEVE the customer and RUN the Tests on the
car whether it is currently overheating or not. If there is a leak, they should
be able to find it. If there is a bad thermostat, they should be able to test it.
etc etc. They wont do that. If I went to a regular mechanic (which I dont have
money for) he would test all those things and come up with a bill/fix it solution,

this is maddening.


i DONT THINK The car is alemon…its pretty good car…my issue is with the
dealer NOT wanting to investigate the ongoing problem unless it happens on a day
when he has thecar? Which seems impossible to comply with. They do get paid
as a dealer for ANY and ALL covered repairs to myHyundai for another 8K miles
or the end of the year, whichevercomes first. I just dont understand WHY
they cant check out all the possible problems without the car currently being
in overheat mode? Is there someone I can complain to for this specific problem?

Look for the 800 number in your owners’ manual packet. There should be a booklet in that packet that provides the process for following up unresolved problems.

They can diagose it when it’s cool of they want to.

Hi I already called the hyundai people…they agree with the dealer that i have to bring it in When it is overheating.

I just got back from driving it and the needle was IN THE RED (I was running the A/C
its hot here today and the dealer told me running the A.C helps…?) but it didn’t
help and I had to switch to HEAT…very HOT and the needle went down but slowly,
so I turned the car off, the needle went down to C COLD. When i turned the
car back on and drove up the small hill to my house it quickly climbed to
HOT H again, so I took a photo of the dial to show the dealer and then turned off
the engine and it cooled down.

3 mins later I drove it again up all the hills here (little ones) and it NEVER
overheated again!!!

I am stumped here!!! really stumped… maybe it IS a loose fan as someone
suggested and going up hills makes it loose? GRRRRRR

Sorry to hear that they’re “blowing you off”. And they ARE.

They can check and test the
T-stat (although it’s cheaper to just replace it)
temp sensor that operates the cooling fan
cooling fan
flow (water pump and flow)
radiator cap
pressure test the system
compression leakdown of the cylinders (checking for that “internal” coolant leak)
and probably a few things I’ve missed (guys, jump in).

Until they’ve done these things they haven’t even tried.

thank you I totally agree. I have never had over all these years anyone say that
they cant repair a car if they cant duplicate the problem on that day. Most
want to make money and find problems. I pointed that out to the dept head at
Hyundai dealer and asked if it was because the repair is free, that they dont want
to bother? He said it isn’t free…hyundai has to pay for every repair under the
warranty so they will get paid. They are just jerks. He isn’t, but I am afraid
to bring it in when it is not OVERHEATED because I did that once with the service
manager and I got sold a SUPER FLUSH which did nothing to help at all.

thanks for your suggestions and your patience.

Take notes of all the symptoms and conditions. When the overheat begins, do you hear the engine cooling fan(s) turn on? Anytime you turn the A/C ON, does the engine cooling fan come on? If you can hear the engine cooling fan(s), can you open the hood, look and listen for the engine cooling fans running?
If the engine cooling fan(s) doesn’t come on, it could be the fan relay, or the engine coolant temperature sensor. The fan relay is a simple swap with another one in the fuse/relay box under the hood. You could ask the kid down the street to swap it.
When the engine is cool, take the radiator cap off, and look into the radiator. If you can’t see coolant, there may be a leak in the cooling system. Warranty may, or may not, cover this.
Observations? Feedback?

thank you for your thoughtful reply. When the car is overheating and I am driving
(it is a noisy car from day one) I cant hear anything.

My local mechanic (not covered by warranty of course) looked under the hood briefly
and saw that the small overflow bottle next to the radiator was empty. He put
some more fluid in it, but I believe we could see antifreeze in the radiator itself
at that point. If I go to thecar now and the bottle overflow is empty, does that
then mean it is a coolant leak? My bumper to bumper warranty is in effect
for 50,000 miles or the end of this year, whichever comes first. It SHOULD
cover leaks, radiator, etc. not brakes, shocks rotors things like that.

I will check the hood now when it is cold to see the radiator and the overflow

Yes, an empty overflow bottle generally means that there’s a leak.

The common term “overflow bottle” is actually a misnomer. It’s actually a “coolant reservoir” and is an important part of the overall system. When the engine heats up, the coolant exapnds and builds pressure. At (usually…spec is stamped on the cap) about 16 PSI, the radiator cap allows excess pressure to be released into the bottle, keeping the pressure from overbuilding. When the engine cools and contracts, the radiator cap allows coolant to be drawn back in from the reservoir, keeping the system full. The level in the bottle goes up and down as the temperature cycles.

If you have a leak, the pressure causes the fluid pressure to relieve itself through the leak rather than into the reservoire. Then every time the coolant in the engine cools and contracts, it draws even more fluid in from the reservoir. But since it’s expressing excess fluid out the leak when it heats up, the reservoire doesn;t get refilled. So the reservoir keeps running low. The level keeps dropping but never going back up.

And, by the way, since fluid not under pressure boils easier than fluid that’s pressurized, a leak can contribute to overheating.

You need the cooling system pressure tested, the radiator cap tested or replaced, a new T-stat, and even a cylinder pressure leakdown test of it’s still not fixed. A leakdown test is one where air is pumped into the cylinders and the pressure is monitore dto see if it’s holding pressure. That checks for headgasket leaks.

Hi I checked the overflow bottle when the car was cold (since last night parked)
and there was NO water/antifreeze in the overlow thing. There was antifreeze viisble
in the radiator when I took off the cap though…not to the top but at the base of
the neck. ???

thanks. I am going to compile a list of everything everyone wrote here and
bring it to my dealer and ask that he test for all these things whether or not
the car is hot when I bring it in.

thanks so much for your help.

Let us know how you make out.

will do and thanks again everyone out there.

Ok, here’s what happened. My car badly overheated this past Monday, so I brought it
to the dealers and spoke to the dept head (service) He listened and sent a mechanic
out to drive the car with me. we WERE able to get it to overheat. he tested the coolant temperature when it was on RED HOT H, and it showed it still cool…should
have shown a rise in temp, but didn’t.

He decided that it is a negative battery cable causing the sensor to misread
overheated when in fact it isn’t. he said its an electrical system issue…
that the battery cable is giving an erroneous signal which screws up the
sensor. They are repalcing the cable and sensor itself.

Meanwhile they say they have done coolant system tests and compression tests,
etc. and have found nothing else wrong. Guess that’s good. The mechanic was
very knowledgeable and nice as was the new service writer I got.

I am hopeful this solves it, but who would have thought it had anything to do with
a battery cable??? That is so weird. I am not a mechanic so not sure I even
understand how one effects the other either. Your thoughs?

I too think it’s weird, but if the actual coolant temperature is fine and the gage says HOT then it has to be either the sensor or a cable (wire). Perhaps he was referring to a bad ground and something got lost in the translation.

Anyway, it’s good to know it isn’t an actual overheating problem. Thanks for posting the results.

I think he did mention a bad ground, but he related it to the battery cable too?

I just hope its fixed, but didn’t really expect this explanation. I wont get the
car till Friday (they were ordering parts). If there were a bad ground on the
battery cable, could that have caused the battery to go dead so early on in
the game? I had 36,000 miles on it and the battery died and I had to replace it.

thanks again for everything. You guys were right about the sensor in the end though.

Hi Everyone

thanks for your help and input on my overheating problem. I finally got my car
back and it is fine BECAUSE:

  1. it wasn’t actually OVERHEATING…just registering HOT.

  2. the mechanic test drove it with me when it overheated and he tested the
    actual coolant to compare with temp gauge reading.

  3. He determine that it was actually the negative ground cable on the battery which
    was defective and causing misreads on the temp.

  4. he replaced it (the cable) and how the needle NEVER seems to go above the mid line at all!!!

Alleluia. Would would have thought that?

But I am grateful and this service manager was nicer and everything went fine.

Thanks again.