2006 Hyundai Sonata tries to overheat

Let me first state that two trips to the service dept were not helpful.

If I drive the car at speeds greater than about 50 mph and suddenly stop
(off ramp, traffic jam), sometimes the engine temp gauge starts to rise
like the engine (v6) is trying to overheat. I have tried turning on or off
the air conditioning with little effect. Putting the car in N and running a
fast idle helps a little sometimes. This happens in the winter and summer
(live in Texas). When this event does happen, it does not self correct. I
have popped the hood and do see the cooling fan cycle on and off about
every minute. I used an IR thermometer and measure temps around the
engine and cooling system, and most are about normal, if not a few degrees
higher than normal. I do see (measure)the thermostat opening and closing by
the temp change on the radiator hoses. The only thing that corrects the
event is driving off. At speeds greater than 15 or 20 will slowly bring
the temp back down to normal. If I do drive off and the temps go back to
normal, the next stop will not usually cause another event. The dealer
checked everything with the car when not overheating and all chaeck out ok
(computer fan, sensors, etc.)

I think the fan, although it cycles on and off, does not run fast enough
when on and/or the water pump flow is too low at idle to fully clear the
engine of the hot water from the freeway drive when suddenly stopping.

Anybody seen this before in a Sonata (or other V6 Hyundai)? I guess I have
to drag the service mgr around and get it to happen in front of him. Right
now he sorta believes me, but I can see he does not to want get sucked
into a difficult to diagnose problem like this if he doesn't have to.

Thanks.

 

I believe you, too, but from what you've written, I'm not convinced it's
abnormal. Here's why:

The temperature the coolant must reach for the coolant fan to start
running is higher than the temperature for thermostat opening. When
you're doing highway driving, you either have high coolant flow (due to
engine rpm) or no coolant flow (thermostat shut) and high cool air flow
across the radiator. When you stop, your coolant temperature builds to
the point where the fan starts to run. If your thermostat was shut at the
time, you will have likely built up a significant amount of heat in the
engine, and the low coolant flow (due to low engine rpm) will take a
little longer to create cooling, possibly allowing the temperature to
increase before it actually lowers.

If you see your fan operate, it's doubtful your fan is the issue. Your
fan is pulse-width modulated by the PCM, effectively meaning that the PCM
controls the fan speed. If the coolant temperature were to continue
rising, the PCM would speed up the fan motor as necessary.

 

Exactly how high does the temp gauge go? I've had three sonata and all
three of them the normal temp would be just below the half way mark. When
they got hotter than normal in stop /go traffic on a 100 degree day, it
would still only go just a little over the half mark. The over heat mark is
the last 1/10 of the gauge.

 

How high does the gauge rise? The temperature will definitely increase
while idling in traffic. This is normal. Unless if goes really high, I
don't think you have to worry. You should also see it cycle a little as
the fans cycle on and off.

Matt

 

That sure reminds me of a coolant flow problem.

You may have trapped air in the system, which can cause all sorts of
weird things to happen. I have seen radiators that look full, but have
trapped air. Trapped air can cause mild overheating, false temp gage
readings, and the thermostat to not behave exactly as it should.

Have you tried burping it?

(Don't know if your cooling system is subject to trapped air, but I
KNOW some are!)
-

Bob

 

Thanks for the input.

This only happens maybe once every few weeks, and when it does the temp
gauge will go waaaay higher than at any other time. Many times getting off
the freeway does not raise the temp reading hardly at all.

The fan will cycle on and off even when the temp gauge is far about above
the normal value (slightly below horizontal). So the computer sees a
normal cycle of temp increase, thermostat opens, fan comes on for 45
seconds or so, thermostat closes, fan turns off, all the while the temp
guage is high or very near the red mark. I want to think the temp guage is
wrong, but this situation will last for 10 or more minutes, before I get
nervious and drive off. The temp will then come down to normal and stay
that way. If the temp guage is wrong, why is it wrong only some times and
why does of 'fix' itself when driving off? I'm not sure what in the act of
driving off is helping: the extra air coming into the radiator through the
grill, or the 1800 engine rpm (increased coolant flow over idle).

After taking temperature readings of various locations on the engine and
around the cooling system, I do think the temp guage is valid in reporting
a higher engine temp than normal, at least to some extent.

 

I agree that near the red is cause for concern. But if the fan is cycling
while the gauge remains near red, it does lead me to believe (as you
suggest) that your coolant gauge is probably not reporting the correct
temperature.

Your coolant temperature sensor actually incorporates two sensors, one for
the ECM and the other for your gauge. Presuming that your coolant
temperature is normal it's possible that the gauge portion of the sender
may be faulty, that there is an intermittent short in the wiring, there is
some sort of ground circuit feedback, or the cluster is faulty. Probably
the least likely scenario is shorted wiring, since a short to ground would
put the gauge in the red.

This is one of those situations where a scan tool is an invaluable aid for
diagnosis. With the scan tool, the technician can monitor coolant
temperature through the ECM and compare with the gauge while driving the
vehicle. The largest issue is that it happens only once every few weeks.
Since it hasn't yet been determined whether the coolant is too hot or the
gauge is in error, the dealer will need to duplicate the condition to even
know what sort of problem they're addressing. If you're not ready to leave
the car at the dealer for a tech to drive it to and from work for a few
weeks, the chances of arriving at a correct diagnosis are very poor.

For now, I'd mention it every time I took the car in for other work, but
realize that there's little the dealer can/will do without duplicating the
condition. It's possible you may get lucky while it's there. The good
news is that even if the gauge is accurate, you're not overheating if the
needle isn't in the red. While you report a gauge position that's cause
for concern and indicative of some sort of problem, it doesn't warrant
immediate emergency action (such as stopping to let the engine cool),
either.

 

Sounds like your t-stat may be sticking occasionally. If the dealer
can't diagnose anything else with some certainty, I'd consider changing
the t-stat as they are generally fairly cheap - although I've yet to buy
one for my Sonata so maybe Hyundai t-stats aren't cheap...

Matt

 

Matt, it's almost impossible for a thermostat to close once it's
opened. The engine would have to cool down nearly to room temperature
to make it close back up.

I guess it IS possible for a thermostat to be opening too slowly,
though highly unlikely. I think the OP's laser thermometer would have
caught that.
-

Bob

 

Try burping it.

Even a little trapped air in the system can fool the temperature
sending and sensing, and cause the water pump to work inefficiently at
times.

Odds are low trapped air is the problem, but since your problem is
unusual, you may get lucky.

*Park on a mild slope, with the hood slightly higher than the trunk

*Let the car cool to ambient.

*Mash the radiator hose, check for pressure. If none, remove the cap.

*Note the coolant level in the radiator.

*Start the car, and watch for large bubbles to burp in the radiator.

*If there are significant large burps, and the coolant level drops,
there's your problem. Run it until all burping stops for a minute or
so.

*Top off the radiator and overflow tank if necessary.

Probably won't help, but it's a very cheap thing to try.

Good luck!
-

Bob

 

Air/Burping-

The Mercury Villager and Nissan Quest are notorious for this. The dealer
recommended practice is insane, and the older units come with an air bleed
screw. The newer ones do not. Easy solution- park the car nose up and force
the air out of the radiator while filling.


--
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Another side note- as HT mentioned, ensure that the dealer documents on the
RO each time you take it in about this issue. CYA my friend...in the event
something catastrophic happens, you have it documented...

Steve

--
NW AZ home for sale in growing area near Laughlin, NV-


http://inlandempire.craigslist.org/rfs/370324491.html

http://www.hoobly.com/0/0/383472.html

 

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--
" Don't Ever hold your farts in,
they go straight up your spine
and into your brain and that's
where shitty ideas come from "