coolant smell only when initially starting heat - JeepForum.com
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post #1 of 25 Old 04-26-2017, 07:37 AM Thread Starter
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coolant smell only when initially starting heat

Just bought a 2004 TJ Unlimited. I had a mechanic look at it because it was an out of state purchase and he had noted the faint smell of coolant only upon turning the heat on that quickly went away. I had the seller (used car dealership) pressure test the system and it held pressure for half an hour with no leaks. Picked up the vehicle last week and no problems until Monday when I looked under the hood to show a buddy and happened to notice a small amount of coolant around the radiator cap and a small drip from the hose that connects the reservoir. I figured maybe there was a leak in these two parts because if the cap was bad it wouldn't have been picked up by the pressure test because that's off during the test. Last night I changed the cap and put a band clamp around the hose and there was a small and normal amount of spillage of collant during this change. I have been checking everytime I drive for leakage and there is none around the cap or the hose now. There is no puddle in the passenger side, there is no excessive fogging so I don't think its the heater core.

however, There is still a faint smell of coolant for about 2 seconds whenever I initially turn the heat on and then it dissipates. If I turn the heat off and wait 30 seconds and do it again I will get the smell again and then it dissipates.

Anyone have any ideas what could be going on? Is it possible that there could just be burning off residual coolant from the engine? Its been pouring all night and I did rinse down the engine last night but im not sure.

Thanks!

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post #2 of 25 Old 04-26-2017, 08:11 AM
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In the TJ the heater core is always in the "coolant loop" meaning that if coolant is flowing then it is flowing through the heater core. If your tech did the pressure test correctly the heater core would have been exposed to the pressures applied by the test. If those pressures held there is a good chance you do not have a leak.

That being said, the test is applied via the radiator, where the cap typically is in place. So the one thing that doesn't get tested is the radiator cap itself, which is a very important working component of the cooling system.

Your best bet is to first replace your radiator cap with a new 18lb cap. It is most likely that the cap is not holding pressure, which would explain the coolant at the cap and at the reservoir. When you first turn on the heater some air from in and around the engine compartment gets drawn into the cabin, hence the odor.

You may need to replace some coolant as well, if the radiator has not been holding pressure properly. It just depends if the coolant reservoir overflowed at all while driving, something you may not notice.

Good luck.

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post #3 of 25 Old 04-26-2017, 08:14 AM
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I'd check to make sure the hose leading to the overflow bottle isn't clogged. That could cause it to leak out at the radiator cap or overflow hose when you shut the vehicle off.

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post #4 of 25 Old 04-26-2017, 08:16 AM Thread Starter
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Yeah I did replace the cap and there have been no visible leaks around the cap since I did that. How long would a little dribble of coolant continue to be smelled for if the problem has stopped? Also, the coolant reservoir level has not changed visibly since ive owned the jeep.
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post #5 of 25 Old 04-26-2017, 08:31 AM
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Sorry about that, totally glazed over the part where you had already replaced the cap .

Since you just did it then I'd give it a day or so for all the coolant to "burn off". Even a small amount has quite a pungent smell and once leaking while driving it gets sprayed all over the engine compartment.

However, in my experience the smell goes away within a heat cycle or two at most if the problem has actually been fixed. If it persists then you may have a leak that only rears it's ugly head at temperature. I had a leak at the mating surface of the t-stat housing once that passed pressure tests and only leaked when the system was at temperature, and even then it was hard to spot as the coolant will burn off as soon as it escapes.

FYI, I've had leaking heater cores and in my experience even a small leak will very typically cause fogging when you first turn on the heat, so I second your notion that it's probably not the heater core itself.

Good luck

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post #6 of 25 Old 04-26-2017, 08:53 AM Thread Starter
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well to be fair, when I start the defroster (not the lower heat for example) my windshield will fog up for about 2 seconds but then the defrost function actually works. I think its just condensation though from the temperature difference. Like I said, its been really wet and cool here the past few days
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post #7 of 25 Old 04-26-2017, 09:44 AM
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Quote:
Originally Posted by Worshiper View Post
well to be fair, when I start the defroster (not the lower heat for example) my windshield will fog up for about 2 seconds but then the defrost function actually works. I think its just condensation though from the temperature difference. Like I said, its been really wet and cool here the past few days
I know you said they pressure tested the system but that symptom sure sounds exactly like a leaky heater core. The Defrost function also runs the A/C compressor to dehumidify the defrost air which overcomes that but that initial fogging and the coolant odor you keep smelling makes me think heater core leak.

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post #8 of 25 Old 04-26-2017, 09:51 AM Thread Starter
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Originally Posted by Jerry Bransford View Post
I know you said they pressure tested the system but that symptom sure sounds exactly like a leaky heater core. The Defrost function also runs the A/C compressor to dehumidify the defrost air which overcomes that but that initial fogging and the coolant odor you keep smelling makes me think heater core leak.
Yeah I know. Me too originally which is why I was freaking out a bit but theres no fluid in the passenger cab at all and the fogging is only for a split second and no when the heat is running and the defroster is not. So im not really convinced.
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post #9 of 25 Old 04-27-2017, 10:31 AM
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I would perform the pressure test again with the hot water control valve open.


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post #10 of 25 Old 04-27-2017, 10:36 AM
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I would perform the pressure test again with the hot water control valve open.
There is no hot water control valve in a Wrangler TJ. Hot engine coolant flows through the heater core 100% of the time whether the heater is running or if you have the A/C on.

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post #11 of 25 Old 04-27-2017, 11:14 AM
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There is no hot water control valve in a Wrangler TJ. Hot engine coolant flows through the heater core 100% of the time whether the heater is running or if you have the A/C on.
DOH!

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post #12 of 25 Old 04-27-2017, 06:21 PM
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Originally Posted by Worshiper View Post
Yeah I know. Me too originally which is why I was freaking out a bit but theres no fluid in the passenger cab at all and the fogging is only for a split second and no when the heat is running and the defroster is not. So im not really convinced.
Keep a close eye on the condensate drain tube rather than looking for coolant on the passenger floor, if the core is leaking it should show up there.
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post #13 of 25 Old 04-27-2017, 06:44 PM
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Keep a close eye on the condensate drain tube rather than looking for coolant on the passenger floor, if the core is leaking it should show up there.
X2. It is normal for pure water (condensation from the a/c system) to drip out of that tube but coolant should not be in the water.

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post #14 of 25 Old 04-28-2017, 04:53 AM
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Something like this: https://shop.advanceautoparts.com/p/...75cs/7010041-P may help you find a leak.
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post #15 of 25 Old 04-30-2017, 11:54 AM Thread Starter
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Originally Posted by Jerry Bransford View Post
There is no hot water control valve in a Wrangler TJ. Hot engine coolant flows through the heater core 100% of the time whether the heater is running or if you have the A/C on.
So would I be correct in assuming that if there was something wrong with the heater core I should smell coolant or fog up the windows even when the heat is off?
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