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coolant smell only when initially starting heat

8K views 24 replies 9 participants last post by  Jerry Bransford 
#1 ·
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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#2 ·
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. :cheers2:
 
#4 ·
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.
 
#5 ·
Sorry about that, totally glazed over the part where you had already replaced the cap :drool:.

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 :cheers2:
 
#6 ·
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
 
#7 ·
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.
 
#17 ·
ok so update... I brought is to my radiator guy and had him take a look. He thought he saw a leak on the passenger side of the lower part of the radiator because there was a small puddle there and he put what looks like kitty litter into the radiator and said it may fix it. It did not. I still smell coolant but I don't see that wet spot on the radiator anymore... the plot thickens.
 
#19 ·
you might have a hose clamp seeping on the heater core as it cools off, try plugging the heater core off to check for the smell. other wise just deal with it till it gets worse.
try laying cardboard under the jeep over night see if you get drips.
 
#20 ·
He thought he saw a leak on the passenger side of the lower part of the radiator because there was a small puddle there and he put what looks like kitty litter into the radiator and said it may fix it.
You can't pass a pressure test with a leak large enough to cause a "puddle". Sounds like the dealership either screwed up the test or worse they simply lied. In my experience having an independent mechanic look at any potential issues is better than letting the dealership who is trying to sell you the car do the diagnosis or inspection.

Throwing stop leak junk at the problem is at best a temporary solution and at worst known to gunk up your coolant system in very undesirable ways. I would eliminate this mechanic from the list of folks to which I bring my vehicles. I'd also recommend you not let anyone put things that look like kitty litter or anything that doesn't look like coolant into your coolant system.
 
#22 ·
update...it was th heater core. I bypassed it and the smell was gone so i bit the bullet and just replaced the heater and evaporator core. I was told the coolant was very acidic so I guess it wasn't changed in a while. Any suggestions as to what fluids I should be replacing prophylactically on this jeep? 2004 new to me. brake fluid maybe? the brakes do feel a bit spongey
 
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