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Engine Overheating, No Heat, P0305

Hi all, I have a 2010 Acura MDX that has been having 4 different problems for the last 3 years.

  1. One set of problems relate to overheating. This started with dried coolant I found all over my engine area and radiator. My engine started overheating after that and I had to top up coolant every week. I took it to a mechanic who replaced the radiator, hoses, thermostat, water pump and timing belt. The overheating continued to happen. I panicked and poured stop leak and that greatly helped although I still needed to top up coolant every month or so. I have tried to burp the system several times but the air is never fully gone from the cooling system. A year ago the heat stopped working in the left side of the car. It partially works on the passenger side. However, cooling did work both side this past summer, although not ice cold. I also hear a whooshing noise whenever I accelerate first time in the day. Are these symptoms of a head gasket leak? I saw a post by Honda blackbird that said it might be.

  2. I have a P0305 code engine cylinder 5 misfire. This makes my car drive rough and I fix it temporarily by clearing the code and the car runs fine again until the next time the code appears. I’m guessing i caused this when I changed the spark plugs in my car and one of them got stuck and I was never able to remove it. Could this be causing the misfire?

  3. Another problem with the car is I have to manually turn my AC on and off. The AC will not turn on or off with ignition. This problem started after I took my car to AAMCO for a transmission electrical issue for which they said they changed the computer and that fixed the engine running hard problem. AAMCO refused to look at my car afterwards when I told them they didn’t fix my problem completely. Could this be a simple relay problem?

  4. My low battery warning perennially appears during winter. I have checked for parasitic drain and there doesn’t seem to be any. I do have an aftermarket radio but there is no parasitic drain from it. I have replaced 2 batteries in the past 3 years and the problem always reappears. The good thing is that the battery hasn’t died and always starts the car so far. I’m careful not to let #3 above cause the battery drain.

I know I have a suite of problems and would appreciate if someone took the time to help. I’m not sure if any of my problems are related.

sounds like a real handfull the last 3 yrs. you used stopleak and probably have a headleak and clogged heater core now which on their own would be a fairly big issue but you have other issues. if you could have the sparkplug issue fixed you still have a leaky head gasket. maybe they could fix the plug thread while the head is off?


Thanks for taking the time. Yes, I’ve had a harrowing time with this car. I’m trying to put all my issues together so I can resolve them in the proper order. Any further suggestions are welcome. Or do you think I should just try to sell it and start a new chapter?

Youv’e let these problems bug you for 3 years and haven’t gotten them fixed. Do you honestly think you’ll actually fix them now? No, you won’t, time to trade on a newer vehicle.

Well, I agree with you and I was preoccupied with work and have some time now to think about what to do with the MDX. which is why now is the time for me to decide whether to fix vs trade it in given trading it in would be getting very little value for it. I’m also looking for any feedback whether the assumptions about my problems are correct. Can someone help with giving me a number for fixing the above issues, so I know better while negotiating a repair price?

I doubt if you can negotiate a repair price. First of all , you don’t want to tell the shop to replace something because that will not be warrantied by the shop if it does fix anything. Second , most shops use a price guide that gives an estimate for how many hours it takes for each job. The only thing you can do is see if the diagnostic fee will be waived if they get to do the work.

With the types of problems this vehicle has there is absolutely no way someone over the net could come close to a close figure. Someone could try, but in real life it’s probably going to way different. The best thing to do is to take it to 2 or 3 shops and get estimates. Be sure to be honest and thorough with your description. When you find the right place there will probably be no bargaining for repair costs. The estimate is usually what they charge, unless there’s unexpected problems.

Thanks appreciate it

First step would be to resolve the overheating / air in the cooling system issue. Getting that resolved could fix the heater problem, and would most likely fix the whooshing noise when you first start the car. I’d recommend having a shop check to see if the head gasket is leaking and go from there. If the head gasket is bad, it might be time to let the car go, depending on the mileage and overall condition of the car. Sounds like there are several issues with the car. I’m not sure it’d be worth paying a shop to repair the head gasket plus the other issues…

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This does not fix anything by just clearing the code.
You either are imagining it runs better, or it’s a coincidence.

You have a headgasket leak. Coolant is leaking into the #5 cylinder, fouling that sparkplug, causing the rough idle.



Thanks Yosemite. I will have that checked out by the shop. How sure are you about that theory?

Thanks john.

Without having the car in front of me and doing other tests, I would say 80%.
If I had the car to examine it may be 100%


Thanks, my car is at a shop right now and you were bang on target. The shop is saying they cant be sure if it’s only the head gasket or the head needs to be replaced as well. Does that make sense?

Can the clogged heater core be fixed with a coolant flush or will require a new heater core?

Also, any idea what #3 in my original post could mean? Would it be a relay issue or something wrong with the transmission computer programming? Appreciate the advice.

Describe what you mean by the AC won’t turn on and off using the ignition switch? Do you mean the AC continues to run when you turn the engine off? I don’t see how that could happen. Or do you mean the AC doesn’t automatically turn on when you start the car? If that’s the only problem, probably best just to use the work-a-round of turning on the AC by tapping the AC button after you start the engine. Trying to figure out why it doesn’t happen automatically is possible to solve but probably will be labor-time expensive, and hard to justify the expense when a tap of the button works almost as well.

If I had that problem I’d have probably bypassed the heater core as a test to see if that affected the overheating. You might still want to try that, esp if you continue to hear bubbling noises.

I meant that the AC continues to run when the engine is turned off. So, I have to manually turn the AC off everytime when I turn the engine off.

Also, another update from the shop today - the mechanic said I would be better off replacing the engine with a used one of similar mileage (~100k miles) and that will prevent expensive repairs down the road, even if the head gasket is replaced. He said the head gasket repair will cost 2000-2500 and a new engine including labor will be 3000. Any thoughts? I’m leaning towards replacing the engine.

The AC compressor can’t be running with the engine off, so I presume you mean the blower motor in the passenger compartment remains running. And you have to manually turn it off when you turn the engine off to exit the car. The blower is used for both AC and heating. I can see how that’d be problematic b/c if you forget to turn the blower off the battery will run down. Unfortunately I don’t have a clue why that would be happening. On a 2010 that function is probably implemented by the car’s body control module. You may need to have that module replaced.

I think you’re right. It’s probably only the blower running, but the AC console remains on. Does anyone know if this could be a relay problem or a problem with the transmission computer programming that was done?

The engine has been overheated too many times, and may not run properly, even with a new head gasket. A low mileage used engine, or quality remanufactured engine–with a reasonable parts and labor warranty is the way to go. Make sure the radiator is replaced with a new one, as the sealant could have plugged up part of it, which will result in overheating under load.

What all is included for this $3000, and how much of a warranty is being provided?

your mdx is about 10k retail with no issues. you could spend 3k on a used motor and have no issues with install. you could sell it for 7k as is if you get really lucky and find a guy who understands the issues and will pay that much. but you probably wont find a guy like that. you could buy another rig for 7k or maybe 10k or maybe more. it might not have any issues.