# 2004 Hyundai Sonata knocking sound and hot smell **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [February 22, 2016, 2:28am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579 "2016-02-22T02:28:35Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Millie33](https://avatars.discourse-cdn.com/v4/letter/m/59ef9b/32.png) [@Millie33](https://community.cartalk.com/u/Millie33)\ **Post date:** [February 22, 2016, 2:28am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/1 "2016-02-22T02:28:35Z")
My car is a 2004 Hyundai Sonata with 260,000 miles. Regularly maintained and has been an excellent car. However, a few days ago, while driving it with the heater on, the car begins to smell hot,both inside and outside the car. My husband has checked the oil, battery, and coolant levels…everything appears normal yet when I tried to start it one day, the car made a loud knocking sound under the hood, battery light came on and the car never started. Any ideas as to what has happened would be appreciated. ---
**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\ **Post date:** [February 22, 2016, 2:45am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/2 "2016-02-22T02:45:33Z")
> ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [February 22, 2016, 3:03am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/3 "2016-02-22T03:03:02Z")
“Regularly maintained” has different meanings to different people. As a result, my questions are… …does this engine have a timing belt? …and, if so, when was the last time (in terms of both odometer mileage and elapsed time) that it was changed? My theory–subject to change upon more information–is that the car has more than one problem. It is entirely possible that a small amount of coolant seepage (either under the hood or from the heater core) produced the “hot” smell. Then, subsequently, and with no connection to the smell, the timing belt may have snapped, thus causing the knocking sound while trying to start the engine, and preventing the engine from starting & running. ---
**Author:** ![Millie33](https://avatars.discourse-cdn.com/v4/letter/m/59ef9b/32.png) [@Millie33](https://community.cartalk.com/u/Millie33)\ **Post date:** [February 23, 2016, 1:39am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/4 "2016-02-23T01:39:42Z")
Thanks for your help. ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [February 23, 2016, 3:14am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/5 "2016-02-23T03:14:17Z")
You’re welcome Millie, but…aren’t you going to provide the answers to the questions that I posed regarding a timing belt? ---
**Author:** ![knfenimore](https://avatars.discourse-cdn.com/v4/letter/k/9fc348/32.png) [@knfenimore](https://community.cartalk.com/u/knfenimore)\ **Post date:** [February 24, 2016, 12:08am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/6 "2016-02-24T00:08:56Z")
A quick search says this car has a timing belt. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [February 24, 2016, 12:42am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/7 "2016-02-24T00:42:32Z")
It sounds to me like the engine overheated and there’s possible damage. I strongly urge you to get this looked at by a reputable trusted shop. Hopefully the timing belt has simply popped and the engine isn’t an “interference” design. That’d mean the fix would be a replacement belt & associated parts (tensioner and water pump perhaps, and a crank seal). It won’t be cheap, but it’ll be a heck of a lot cheaper than a new car. ---
**Author:** ![Millie33](https://avatars.discourse-cdn.com/v4/letter/m/59ef9b/32.png) [@Millie33](https://community.cartalk.com/u/Millie33)\ **Post date:** [February 24, 2016, 5:34am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/8 "2016-02-24T05:34:58Z")
The sonata is a V6 if that helps. We have had the belts changed regularly…everything done according to maintanance Manuel. A neighbor came to look at it and he seems to think it has a blown head gasket. I simply cannot believe that this car, that ran like a top, is now toast. I know it has 260,000 miles on it but there were no warning signs…except for the hot smell. Does a blown head gasket mean new motor? I appreciate all the comments. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [February 24, 2016, 5:52am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/9 "2016-02-24T05:52:16Z")
It might turn out to be a blown headgasket, but that’s also a common guess when a car overheats. If your neighbor is knowledgeable and looked at the car, he’ll know what to look for and I’d trust his word. A blown headgasket has some pretty clear symptoms. If he isn’t, you’ll want a good shop to look at it. Note that a blown headgasket by itself doesn’t necessarily mean a new motor, but the knocking if caused by overheating is probably bearing damage, and that’s bad. The bearings that first get damaged are major components of the engine’s insides, and on an engine that age it means a rebuilt or a boneyard replacement motor. HOWEVER, don’t give up without getting a second opinion. Even from a good shop, a major-damage diagnosis deserves a second opinion. ---
**Author:** ![wentwest](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/wentwest/32/6073_2.png) [@wentwest](https://community.cartalk.com/u/wentwest)\ **Post date:** [February 24, 2016, 6:00am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/10 "2016-02-24T06:00:35Z")
Lots of possibilities, I guess, but I’d suspect a failed water pump. However, without a little checking out of symptoms it’s really not possible to know what’s really going on. You need a real mechanic to check it out. Search the “Mechanics Files” on this website. ---
**Author:** ![Millie33](https://avatars.discourse-cdn.com/v4/letter/m/59ef9b/32.png) [@Millie33](https://community.cartalk.com/u/Millie33)\ **Post date:** [February 24, 2016, 6:24am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/11 "2016-02-24T06:24:01Z")
Thank you all for the comments. I will definitely have it diagnosed by a reputable mechanic. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [February 24, 2016, 8:50am UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/12 "2016-02-24T08:50:22Z")
260 K, could be most anything. That’s approaching the practical economic lifetime limit on most vehicles. If this turns out to be inexpensive to fix, be aware there’s more problems coming probably. And those might not be so inexpensive. Odors when the engine is warmed up are usually just fluid leaks that are getting on hot engine components and evaporating and making a stink, like oil from a leaking valve cover dripping on the exhaust system. I’d guess the reason the car developed the knocking noise and now won’t start is the timing belt has failed. A mechanic can check that guess fairly easily. ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [February 24, 2016, 7:44pm UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/13 "2016-02-24T19:44:57Z")
**“Odors when the engine is warmed up are usually just fluid leaks that are getting on hot engine components and evaporating and making a stink…I’d guess the reason the car developed the knocking noise and now won’t start is the timing belt has failed…”** I’m glad to see that George agrees with what I stated in the second post in this thread: _My theory–subject to change upon more information–is that the car has more than one problem. It is entirely possible that a small amount of coolant seepage produced the “hot” smell. Then, subsequently, and with no connection to the smell, the timing belt may have snapped, thus causing the knocking sound while trying to start the engine, and preventing the engine from starting & running._ ---
**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\ **Post date:** [February 24, 2016, 9:54pm UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/14 "2016-02-24T21:54:46Z")
**_Food For Thought. Is This The 2.4L Engine? I Understand That They Are Notorious Breaking Timing Belts If Not Replaced According To The Manufacturer’s Replacement Requirements As Found In The Owner’s Manual._** However, the balance shaft belt is not mentioned as a maintenance item (?) and is often not replaced when the timing belt is renewed. When the balance shaft belt breaks it frequently (usually?) breaks the Crankshaft Position Sensor. Without a sensor in place it won’t start or run. I’m Noticing That Many Times The Timing Belt Is Replaced And Not The Balance Shaft Belt During Timing Belt Replacement. Also, am I thinking correctly that one of the balance shafts also drives the oil pump? That could be problematic and would create a knock in short order. _ **CSA** _ ---
**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\ **Post date:** [February 24, 2016, 10:58pm UTC](https://community.cartalk.com/t/2004-hyundai-sonata-knocking-sound-and-hot-smell/92579/15 "2016-02-24T22:58:27Z")
**_I See It’s A V-6. Is That A 3.0L? CSA_**