2005 honda civic ex, my coolant smells like exhaust, and I have been magically losing coolant/overheating the past month. It seems slow though, because it lasted 3 weeks between the last coolant refill before it started overheating again. Also, the reservoir was full the last time it overheated, with a brownish hued coolant color...

Can exhaust smell like coolant without it being a blown head gasket?

Edit: No, it can't, it was a head gasket. :'( .... Edit 2: OMG....P2646 after Head Gasket Replacement....WRONG or NO OIL?

3 Answers 3


If you're absolutely sure that you smell coolant out of your exhaust pipe, then that means it's leaking into one or more combustion chambers, getting burned up and emitted out of the exhaust. The only two possible ways that antifreeze will make its way into those chambers on its own is a 'blown' head gasket or intake manifold gasket. All that means is that one of those gaskets are damaged or worn in a specific location. The symptoms can vary by the location of the gasket damage, as well as the severity of the damage. Sometimes, the damage is only between the coolant channel and combustion chamber. This means that coolant is leaking into the engine, but not into the oil. That means you won't find oil in water or water in oil. That sounds like what's going on here. It also sounds like the damage is small enough that the leak is slow, which could explain why you're not seeing a bunch of white smoke out of the exhaust; just smelling it. Paulster2 is correct here about the fact that it's just a matter of time before it gets worse, as well as testing for hydrocarbons in the coolant to confirm a gasket problem. You could do a pressure test, too, but the former will definitely be conclusive. Also, I agree that you should completely flush the mixture of standard and extended life coolant out of the system completely. I know it was probably an accident, but they're not meant to mix as they are chemically different, resulting in reactions that can be problematic, like the sludge Paulster2 mentioned. Anyway, to sum up, head gasket failure is more common but intake gasket failure is the only other way exhaust could smell like coolant, especially if oil and coolant aren't mixing. Good luck.

Edit: By 'on its own', I meant without mixing with oil in case there was any confusion. There's more ways for it to end up in combustion chambers in that case. Bad oil cooler + problem causing oil to burn in chambers, cracked head or engine block and possibly more. I suppose it's possible for a cracked head to be cracked in such a way that coolant is leaking into chambers but not oil but, in my experience, this is extremely rare.

  • head gasket confirmed :'(
    – Prodnegel
    May 2, 2017 at 13:53
  • Sorry to hear. It's good that you got it taken care of immediately after these inquiries though! May 2, 2017 at 23:29
  • 1
    My pleasure buddy. Thx for being so receptive to our suggestions. Many people at work ask my advice but give in to skepticism-- until they're broke down on the side of the road and end up paying more than if they had just listened. I truly don't understand it. :D May 4, 2017 at 16:56
  • I think it helps being an engineer working on similar technology. Although I may want to look into every last scenario possible, when it comes down to it, any problem no matter how big or small can permanently damage your system. I think once you understand the complexity involved in engine systems, you get a greater appreciation for even the smallest of problems. I think the general public nowadays is just so used to things working 99% of the time, that ignoring small problems doesn't seem like a big deal to them.
    – Prodnegel
    May 4, 2017 at 18:37
  • I would bet that cars are probably the most complex things that most humans use on a daily basis, without even knowing it.
    – Prodnegel
    May 4, 2017 at 18:37

Head gasket is toast at the very least. If you're lucky. If you're not lucky, then your cylinder head could very likely be cracked as well. That gets very expensive very fast.

Sorry. 😢

  • why??? and no worries friend. engineers like ourselves get paid well :)...it will be a hassle though :'(
    – Prodnegel
    Apr 29, 2017 at 1:38
  • @Prodnegel :) still sucks. So is the question why is the gasket toast or why do I say that? Apr 29, 2017 at 1:39
  • why gasket toast definitely? I don't see any smoke at all coming from exhaust
    – Prodnegel
    Apr 29, 2017 at 1:39
  • You noticed a brownish color in your antifreeze, like oil is mixing? Apr 29, 2017 at 5:17
  • @Prodnegel you may not always get smoke. Simple fact - coolant shouldn't be brown or smell like exhaust. If it does, there's got to be some kind of contamination. Apr 29, 2017 at 5:24

It is very unlikely it's anything other than a blown head gasket. The three major clues are the exhaust smell, brownish colored coolant, and missing coolant. The overheating is a problem of losing coolant. At this point it's just a slow coolant leak. It will get worse with time. The occasional overheating will make it so. If you check the oil, you'd probably find there is coolant in the oil as well. If so, the oil is contaminated. As this happens, it becomes acidic and will start to destroy the bearings if left for any appreciable amount of time. If you have the money as suggested, get it fixed sooner rather than later or junk the car. The longer you leave it, the more damage will be incurred.

  • oil is perfect. Hasn't moved an inch since my first overheating 3 weeks ago. I also get faint smells of coolant through the vents in the car...but she runs fine. I overfilled the reservoir on the first overheating, so I think that played into it. Also, I mixed orange with green coolant, making me think the yellowbrown coolant color...It is just so weird because she has ran 100% fine
    – Prodnegel
    Apr 30, 2017 at 0:46
  • Even with a blown head gasket the engine can run fine ... At least it will until it doesn't. It sounds to me like you've already made up your mind on what the issue is and you're waiting until someone states it so you can agree with them. If you want to tell if it's a head gasket leak for sure, get a test kit which tests for hydrocarbons in the coolant. This test is conclusive. Also, you need to get the mixed coolant out of your cooling system, as mixing green/orange tends to create sludge and will clog up your cooling system. Apr 30, 2017 at 0:53

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