A frustrating and costly problem with a 2014 Honda Civic. I had the radiator flushed in late 2021 at the dealer. It had heat that winter but next summer I noticed it didn’t. The radiator then went out in fall 2022 and I had that replaced at a shop in Buffalo when they discovered a milky substance in the radiator. They later replaced the heater core in December 2022 (backorder). In February 2023 there was no heat again. Another repair shop in Cleveland replaced the radiator and flushed the heater core in March 2023: there was more of the milky substance in the radiator. The heat didn’t work perfectly but still blew warm air. A week later I’m back to essentially no heat. Not sure if there’s a gasket leak or something but my most recent mechanic says there’s nothing in the oil and and doesn’t think it’s a gasket leak. What could this be? It seems unlikely that the dealer put something wrong in my car since my heat lasted for quite a while after the last time they flushed it. Could I have some kind of a slow leak from a gasket, cylinder, cracked engine block, or oil-coolant exchange system? Is this possibly residual stuff that my mechanics should have done a better job of removing? It seems unlikely to be transmission fluid from what my mechanics have said but I have noticed very recently that my car makes a noise when I press the accelerator from a stop. I’ve spent over 2500 between the radiator and heater core replacements. My car seems to run fine and should be worth around 10K otherwise so I would like not to have to junk it at this point.
Normally my guess would be transmission fluid leaking into radiator via transmission cooler, but you say the radiator was replaced and the milky substance returned? hmm … well, that’s good news in a way, b/c coolant can leak the other direction and damage the transmission. What else? maybe engine oil is getting into coolant via head gasket or other problem. If you have a separate engine oil cooler gadget where coolant and engine oil come in close contact, that would be my first suspect. Any indications of contaminated engine oil?
Has your shop pressure tested the cooling system?
Once you get the problem fixed, suggest to replace coolant with fresh stuff every 2-3 years, even if that is more frequent than Honda suggests. Make sure shop uses the specific coolant Honda recommends.
The transmission cooler/warmer might be leaking CVT fluid into the cooling system. This is a coolant/oil heat exchanger that is mounted on the transmission.
When the heater was blowing cold, was the cooling system found to be low on coolant or just polluted?
Why did you have the radiator flushed in the first place? Did the manual suggest doing so? Or was there a problem?
Yes, that is good news that I don’t seem to have a fluid leak if I can only get this problem fixed. There are no signs of coolant in the oil. I took it to a Honda specialist and they said that there is no way that the coolant could mix with the transmission fluid. I just talked to the mechanic who replaced the heater core and he thinks that any petroleum based product (transmission fluid or oil) would have degraded the hoses in the cooling system. He talked to the distributor of his antifreeze and thinks it’s some kind of stop leak product. He said there was a lot and it was difficult to flush out so maybe there was some left in the engine that got into the new radiator and the heater core. Sorry for the late reply: I didn’t see my email notification that someone had responded.
I just got my car back from a Honda specialist and they told me that there is no way for the transmission fluid and coolant to mix. Perhaps they’re mistaken. They also didn’t talk very much at all. The coolant hasn’t been low since the first time I had the radiator replaced.
The Honda dealer recommended it. I’ve never had heating problems with this car before 2021 and I’ve had it since 2015 with ~14000 miles on it.
Sorry for the redundant replies.
To recap:
It doesn’t seem like antifreeze or oil since my Buffalo mechanic thinks that the cooling system hoses would have been degraded and a Honda specialist I saw claims that there’s no way for the coolant and transmission fluid to mix. Hopefully they’re right. My Buffalo mechanic thinks someone added some sort of stop leak to the system. I don’t see that the cooling system has been pressure checked on my records. The reason I had my cooling system flushed in 2021 before these issues was just because the dealer recommended it at the time.
Update:
The Honda specialist I just got back from tried changing the antifreeze and recommended a heater core flush or replacing the heater core. They think the heater core may have been installed wrong (in Buffalo) which doesn’t make sense to me because when it was flushed after the second radiator replacement (in Cleveland) the heat did come back temporarily for about a day. It still does blow a tiny bit of warm air now at the lowest blower setting and more out of the passenger side vents. After talking to my mechanic from Buffalo today he seems pretty convinced that someone added some kind of stop leak. I see that the dealer who did the initial radiator flush also winterized the vehicle by adding MOC cooling system treatment a few months later. I just looked this up on their website and it looks very similar to their cooling system sealer. I’m thinking maybe one of the technicians at the dealer added the sealer instead of the cooling treatment. The website says the sealer is supposed to be non-clogging but I wonder if that’s still the case after a year sitting in the cooling system. I see warnings about using sealer online and both mechanics I talked to seemed to be wary of using it. No one outside of the dealer has touched the cooling system between the time I moved to Buffalo in summer of 2020 and just before I had the radiator replaced in late 2022. Does anyone else agree that sealant added by a dealer technician sounds plausible? I’m thinking I should reach out to them but I’m not sure what kind of a response I’ll get.
Suggest to ask at a Honda dealership. I expect they’ll say the only substance that should be put in a Civic’s cooling system is the Honda-approved coolant for that engine. Given all the flushing, and it still remains, there must have been quite a bit added.
There seems to be some disagreement whether it is possible for transmission fluid to leak into the coolant. Was there ever, or is there a visible coolant leak? Coolant puddling on the ground? Or in the engine compartment?
I am sorry this happened to you, but the problem started with the “flush”. The only things that should get flushed are the brakes and your toilet. Nothing else. I stopped flushing my cooling systems over thirty years ago when I noticed that all my cooling system problems started right after doing a flush, especially when the flush included any chemicals. Cooling system maintenance should be a drain and refill only. Do not worry about some old coolant being left behind, it wont hurt anything.
Clearly your Honda specialist needs to go back to school because the coolant and ATF can mix. Some “flush” chemicals can and do destroy rubber seals so it is possible that the heat exchanger for the transmission is damaged.
There is likely nothing wrong with the heater core. If they can do a clear water flush of it, then it is not the problem. What they seem to failing to do is burping (bleeding) the system and getting all the air out. Many new engines these days no longer have a bleed screw and have to be burped to get the air out. That takes a little specialized equipment and some time. Some systems will burp themselves.
One last thing, some vehicles now have a pressurized reservoir instead of an overflow tank. Make sure the proper caps are on each. Some systems with pressurized reservoirs have caps that look alike and can get mixed up.
Edit: One last thing, your transmission no longer has a dipstick on it so checking the condition of the ATF is much more complicated. It will take a certified Honda Transmission Specialist, make sure they are Certified for Honda CVT transmissions. If your dealer doesn’t have one, then find a dealer that does. You need to have your ATF checked because if there is any coolant in the ATF, then you are risking damage to a $6k transmission.
Another edit: The condition of the ATF is usually checked via the OBD Port with a specialized scan tool. This might not pick up the contamination. Make sure the transmission specialist knows to pull a sample of the ATF and not to rely on the scan tool.
A cooling system flush is nothing more than a fluid exchange, more effective for engines without accessible block drains than a drain and fill. I have performed many cooling system flushes with several different types of equipment over the years and never damaged a cooling system.
A cooling system flush can be a LOT more than just a fluid exchange. More often than not, other chemicals are involved. Just because you don’t use them doesn’t mean that others don’t either.
Also many people, mostly DIY’ers will flush out their cooling system with tap water, introducing minerals into the system. The minerals plate themselves to the inside of the cooling system reducing its effectiveness.
Even if you are doing a fluid exchange only with a flush machine, can you be sure that you are not cross contaminating your machine and customers vehicles with different types of coolant? Maybe if you work exclusively for a dealer, but then there are dealers that carry and service more than one brand of vehicle.
Drain and fill is the only way I go from now on.
Sorry, I missed you question at the end of this. There is no visible coolant leak and I don’t believe there has been since the radiator was replaced the first time.