If my car has overheating/coolant problems, but no check engine light, is it possible that there are pending codes which haven't became stored yet because I keep refilling the coolant before the pending code has enough cycles to become stored?

2005 Civic EX

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    Possible, yes. Actually the case here? Hard to tell. Is it leaking out visibly somewhere or burning and emitted out of the exhaust? – Mustangguy809 Apr 27 '17 at 22:32
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    Sounds like there's too much pressure in the system. Say, for example, your radiator cap is wearing out and very slowly allowing a tiny bit of air into the system, the pressure increases, causing coolant expansion until too much fluid dumps out of the reservoir overflow. Now you have low fluid. As far as your actual question, you might get pending codes that can't mature because the problem hasn't been consistent for enough cycles, but it's too hard to tell for sure. Did you bleed the air out when you filled it up last? – Mustangguy809 Apr 27 '17 at 23:30
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    I would just get the levels back where they should be when the car isn't warmed up at all, bleed it, and wait to see if it happens again. Fill radiator very close to full. Don't fill the overfill reservoir higher than cold spec line. You can then let the car run for a bit to let the air bubbles out. Then tap it off completely. – Mustangguy809 Apr 28 '17 at 0:29
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    If you want to be sure that it's completely bled, get a very large funnel, and stick that in the radiator fill hole before starting the car to let the bubbles out. Replace cap, check it the next day before starting to tap off the levels if they've dropped. Then just keep checking it for a few days to see if the level continues to keep dropping. That will tell you if there's still a problem. – Mustangguy809 Apr 28 '17 at 0:29
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    Keep in mind that air can get in the system in multiple locations. Water pump housing or gasket, thermostat housing or gasket, old hoses, etc. But let's hope it was the cap and not another defective or cracked system component. – Mustangguy809 Apr 28 '17 at 0:30

There are some codes related to the coolant system for a Honda that could begin pending, such as P0116 through P0118, P0125, P0128, etc. There are also multiple codes that could begin pending from compromised engine and emissions due to a head gasket blow or other damage from overheating, or a defective cooling system component causing performance and emissions problems, though these usually require fewer cycles to mature to DTCs (Diagnostic Trouble Codes).  I realize, per our conversation, that this wasn't the case this time, but for future reference, it could happen. By the way, pending codes do store and can be seen and cleared on your OBD reader, but I'm assuming by stored, you meant becoming a DTC, resulting in a dashboard diagnostics light illumination.

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  • It has not overheated for the past 3 days, but I definitely smell coolant coming from the exhaust...Is there any way coolant smell out of the exhaust without it being a blown head gasket? – Prodnegel Apr 29 '17 at 1:18
  • made a new question relating to exhaust mechanics.stackexchange.com/questions/44036/… – Prodnegel Apr 29 '17 at 1:21
  • Oh, I didn't know you were smelling it out of your exhaust. If you smell it there, coolant is leaking into the combination chamber(s). Usually, it's because the head gasket is 'blown', which really just means part of the gasket is now broken/missing and not sealing 100% anymore. Sometimes it can be the intake manifold gasket, though. However, if your coolant is the standard green colored kind, yet you're seeing a brownish color in it now, head gasket is the leading candidate. Head gasket breaks can vary in size and location. – Mustangguy809 Apr 29 '17 at 4:57
  • So, it's possible that the way it's damaged is allowing only enough to burn that you can smell it but not see a bunch of white, steamy smoke. Check your oil too and see if it's kind of milky off-white instead of normal. – Mustangguy809 Apr 29 '17 at 5:01

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