How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Mike V. Your Own Question
Mike V.
Mike V., Hyundai Technician
Category: Hyundai
Satisfied Customers: 25312
Experience:  I have over 25 yrs. experience on all makes and models. Factory trained for Subaru and Nissan.
Type Your Hyundai Question Here...
Mike V. is online now
A new question is answered every 9 seconds

Hyundai Elantra I have a 2001 Hyundai Elantra. While driving,

This answer was rated:

I have a 2001 Hyundai Elantra. While driving, there is fairly good heat from the heater. However, when stopping at a light or stop sign, the air coming from the heater turns cold. As soon as I accelerate, the air is hot again. The faster I go, it seems the hotter the air is from the heater. I flushed the radiator and the heater core, replaced the thermostat and put in new antifreeze. After drtiving for a while, 5-10 miles, the top radiator hose is hot but the bottom one coming from the thermostat housing is still cold. The temperature gauge reads normal as it has since the car was new.
Any help would be greatly appreciated.
Hi there! This sounds like a possible air bubble stuck in the heater core. Normally the air pocket will sit in there and the air doesn't make the core hot. Then when you accelerate, you are forcing the coolant into the heater core,giving you heat.
It is also possible there is a weak water pump,not pushing the coolant fast enough. I would start by trying to get the air out of the system, if that doesn't work, then go after the water pump.
Customer: replied 6 years ago.

Thanks for getting back so quickly. As for the air bubble, how would I go about getting that out? Also, why will the bottom radiator not get hot after driving for a while? Finally, I forgot to mention that the one heater hose gets hot but the other one is only warm after driving for quite a distance. I am hoping the water pump is not the problem. It looks like a real bear to change.

Thank you.

The water pump is in there pretty deep.
I would try raising the front of the car on ramps. Then remove the radiator cap and run the engine with the heat on, first around 2000 rpms, then at idle. When you have heat at idle, shut the car down and top off the coolant. This should burp the air out of the system. Remember you will have some hot coolant coming out of there so be careful.
Sounds like it might be a possible blockage with the heater core, but it really seems like an air issue. This can also affect the one hot and one cold at the radiator. If the system is low on coolant, it will act this way.
Customer: replied 6 years ago.
Tried putting car on ramps but no success. I'm in the process of removing the water pump now. I'll let you know whatI find. Thanks and have a good evening.
You do the same and yes, please let me know.
Customer: replied 6 years ago.


I just got the water pump off and it looks fine. The seal is not leaking and the inpellers are in good shape and not loose on the shaft. However, since there is so much time involved in getting the pump off, I am going to put on a new one tomorrow. Any other suggestions would be greatly appreciated. One other thing I noticed is when I had the front of the car raised and running it to try to get any bubbles out of the heater, The engine cooling fans both came on yet the lower radiator hose was still cold. Also, when I took out the old thermostat to put in a new one, when I removed the thermostat housing, very little antifreeze ran out. I don't know if this is due to me emptying the radiator first or something else is going on. When I removed the water pump, a lot of antifreeze came out.

Thanks again and talk with you tomorrow.

The only other thing I can think of would be a blockage in the radiator. This seems unlikely because the car is running at the proper engine temp.
Customer: replied 6 years ago.
Well, I relaced the water pump and still no luck. I clamped off the top radiator hoseand squeezed the hose close to the radiator and the antifreeze rose in the radiator. Did the same with the bottom radiator hose with the same results. I would think the radiator would have to be opened if the antifreeze rose in the radiator. Am I thinking correctly or am I missing something? This thing really has me stumped.
You are missing nothing,it has us both stumped.Still has to be air somehow. Just not sure why it won't bleed. I see nothing about any special bleeding sequence on this at all.
I will open it back up for the other experts, maybe one has seen this problem first hand.
Customer: replied 6 years ago.
Hello again: I was wondering if you got any additional information re. the 2001 Hyundai Elantra not giving heat? It did throw heat while driving but not when sitting at a light or stop sign. Now 1 day later, there is no heat anytime. This is my daughter's car and she had a friend replace the top and bottom radiator hoses. I want to be certain they were attached correctly. Does the hose from the thermostat housing go on the top or bottom of the radiator? Also, someone mentioned the head gasket could be blown. However, there is no antifreeze in the oil (oil looks clean and fresh) and no oil in the antifreeze and no heavy white smoke when running. Could the gasket still be blown and if so could that cause no heat? Lastly, would a compression check show a blown gasket no matter where it is blown? I see the head bolt torque is only 18 lbs plus a turn of 60 - 65 degrees. Any help will be greatly appreciated and will also keep me from going crazy at this point.
Not sure if this will help, but the one closest to the battery should go to the lower connection on the radiator. The one closest the head to the top.
I don't believe the issue is the head gasket,the car would normally overheat. It is possible it could lose the coolant, slowly into the cylinders and not fills the engine oil with it.
Personally the best way to check is with a pressure tester on the cooling system. Leave it on for about 1 hour,then pull the plugs and check for coolant on top of the pistons.
Normally you would get a misfire when you start the car after it sits overnight if this is the problem.
You would get the cold air because you get air trapped in the heater core. It is possible this is the problem, but rare without the car overheating. It does happen on nissans alot though.
Here is an image to help with the location of the hoses

2001 Hyundai Tiburon / Elantra 4CYL air intake system by Weapon R
Customer: replied 6 years ago.

Thanks for the info and the picture. Tomorrow or as soon as I can, I'll pressure test and also run a test for combustion gasses in the antifreeze. While I'm at it, I was going to take out the thermostat and see if water circulates with it out. While it is out, I'll have the entire cooling system backflushed. One thing I did notice was looking in the radiator neck there was a large piece and smaller pieces of what looked like a soft cork material. I'm wondering if this is blocking water flow somewhere.

I'll let you know what I find. Thanks and have a good evening

Possibly, maybe someone tried some type of sealer in it and that is the problem.
I have seen some of the sealers block cooling p-passages in the past.
I think what is throwing us is it isn't overheating!
How can it be blocked and not overheating! This is a mind bender for sure.
I have seen it on the Nissans though, head gasket leaking and you wouldn't even know it.
No signs, but a slightly rough idle at first start up, once the coolant is forced out of the engine, runs normal and no overheat.
Customer: replied 6 years ago.

Hello again:

I just read where there is a water temperature sensor or solenoid on the heater core and if it is bad, it will not allow hot water to flow through the heater core. Is this so and if so, where is it, how much of a job is it to check it and replace if needed?

Thanks again for all the time and effort you are putting into this problem. I really appreciate it.

Sorry,I know of no such part.There is a temp probe in the a/c evaporator that will turn the compressor on and off, but I have never heard of anything in the heater core that would do that.
None of the information I have from Hyundai or Mitchell mentions any type thing.
Here is a diagram of the thermostatic switch. It is located behind the glove box and maybe it is the problem. I would first check again to see if the heater hoses are getting hot. If both get hot, then it might be a blend door issue inside the car.
Customer: replied 6 years ago.

Thanks for the information. I wanted to check with you first before I go hunting a non-existing part. Regarding the picture, is this view looking straight in through the glove box opening? Also, what is the purpose of this switch. Is it only related to the A/C or does it control something related to heat?

Thanks again.


This is with the glove box removed so you should be able to drop it and see it.
Now, to the best of my knowledge, this switch is only there to turn off the a/c compressor and keep the evaporator from freezing up.
It may be different for Hyundai, but I don't see a stitch of information about it as far as the heating system goes.
No problem with the help :) Just wish some of it would work!
Customer: replied 6 years ago.

When I remove the glove box and look in, there are not any switches or connectors to be seen. There is one on the bottom of the heater box going up into the heater box. I would think this is related to the A/C though. Is your diagram of a 2001 Hyundai Elantra? Just wanted to check. I have a cleaner in the cooling system and thew thermostat out at this point and drove about 1 hour yesterday. I checked the water level this AM and it was still up in the radiator neck but really dirty. The cleaner is to be left in for 3 - 6 hours total. I'll drive it today some more. When I had the heater hoses disconnected from the tubes going into the thermostat housing and blew through each hose, it was fairly hard to blow through them. I'm hoping the heater core is plugged and the cleaner will loosen up the dirt. I'll let you know after I drive more today.


That is the pic of the,from Mitchell so it could be wrong, Also, back flush the heater core with a garden hose. Run water in and out both directions. Until it comes out clean.
Customer: replied 6 years ago.

When I look at the heater etc through the glove box door, there are no wires, switches or anything like that visible.

Earlier I did back flush the heater core in both directions but when I removed the thermostat housing, the coating inside was tan looking and very waxy and sticky. I'm thinking back flushing may not have gotten rid of all of it or maybe not hardly any in the heater core.. I'll see what the chemical cleaner does.

Talk to you after I drive it some more.

Sounds like a plan to me.Not sure what is up with that picture then. It is showing that as the location, but normally the thermistor is inside the heater box and located in the a/c evaporator.
I hope the cleaner does a good job, you have to have a blockage here someplace. Just not sure where.
Mike V. and other Hyundai Specialists are ready to help you
Customer: replied 6 years ago.

Put in a cleaner, Prestone, and drove car 5 hours. No success. Then I got a cleaner made by Gunk. Drained heater core, left both heater hoses attached to the heater. Removed other ends of both hoses from the tubes on the thermostat housing and raised these ends above the heater core. Poured Gunk cleaner in one hose and added water until cleaner started to come out other hose. Left this sit 4 hours and back flushed heater core in both directions. Next backflushed block and radiator in both directions. Water would not come out of tube on the thermostat housing that has a hose attached to the outlet of the heater core. Flushed water directly into this tube about 20 times and heard a thud. Back flushed block and radiator again and this time water came out the tube previously blocked. Now I am getting fairly good heat driving and still some heat when sitting still. As far as I'm concerned that is OK. The car is my daughter's car and has 190,000 + miles on it and she will be getting another one when she graduates from college this spring.

Thanks so much for all your help and suggestions.

The best to you and your family this Holiday season.


Well, so it sounds like it was a blockage after all and congrats on getting one through school! Mine is out this year to.
Thanks you for the accept and the best you and yours as well!