Bought a 2006 Honda Civic EX (not hybrid) from a mechanic last January. I drove it home for about 20 minutes at about 75 mph. I think he masked that it had a blown head gasket. I have brain damage and missed the red flags. I haven't had or done any work on it.

Heater only works on the left side vents, semi-warm air on the middle vents, and cold air on the right. Local Honda dealership said it was a clogged heater core and recommended replacement. I know you try flushing first so I took it home. Unfortunately, it was January in Idaho so everything is frozen, no water hose to use. I figured I'd put up with it until spring to flush it.

Within a couple weeks, I noticed the coolant was disappearing, but no leaks underneath (parked on dry pavement). I checked the radiator, the overflow tank was nearly empty, there were a lot of particles in it, and it was a murky gray. Under the radiator cap coolant was a couple inches low. I removed and cleaned out the overflow tank, and topped off the radiator and the tank to max line with the Honda-specific coolant.

I checked the oil cap and had to use a wrench to twist it open. The cap underside was light brown/milky. I wiped it off to rule out condensation, but it always quickly turned light brown after driving a bit and wiping again after every drive. I did the funnel above the engine spout in the radiator test and got a bubble about every minute. So combustion gases are in the cooling system, which may also have caused the heater core clog.

It's sat in my driveway for the past four months because I'm frozen on what to do and diagnosing the actual problem. Head gasket repair is more than the car's value (which I also paid almost double it's book value already - remember, brain damage). I don't want to sink another $4k+ to repair the gasket and possibly the other parts.

The Civic has these symptoms:

  • Coolant levels drop very quickly
  • Constantly needing to top up the radiator with coolant
  • Bubbles in the radiator and reservoir overflow
  • Milky discoloration of the oil

However, it does not have these symptoms:

  • Increased engine running temperature
  • Cloud of exhaust fumes when idling, or white smoke coming from exhaust pipe
  • Coolant clearly leaking onto the ground beneath the head gasket
  • There is no loss of oil.
  • Radiator cap seems to fit tight.

I looked into bad intake manifold gasket symptoms, but it does not have:

  • Green, red, or yellow leaks under the car
  • Overheating engine
  • Engine running rough
  • Decrease in power, acceleration, and fuel economy

However, the check engine light came on about a month ago:

  • Code P2646 Rocker Arm Oil Control Valve (A) Stuck On/Off.
  • I cleared the code and was about to buy the part but the code never popped up again.
  • I'm not sure if it's related to a blown head gasket.


  1. Given the symptoms, is it a bad head gasket or what else could it be?

  2. Is the Rocker Arm Oil Control Valve a related problem or something different?

  3. Should I not use a coolant system sealer product, because the coolant and oil seem to be mixing?

  4. Are there any other problems I'm missing?


  • Milky oil on underside of oil cap.
  • Dipstick oil check are clean oil.
  • 2006 Civic with only 84k miles! I verified with a CarFax report.
  • Sounds like a slight head gasket leak, but it might be enough to show up in a compression test, so ask for a quote for just that. You don't mention mileage, so bad compression might also be worn piston rings. Remember the head gasket separates four different spaces: the cylinders, the cooling system, the oil feed and drain system, and the outside world. Symptoms are highly dependent on the exact location of any leaks. Commented May 3, 2023 at 9:32
  • Doh! I just updated the original post that is has 84,000 miles, which is fantastic for a 2006 car. I didn't believe it at first so I bought a CarFax report. It's legit. Commented May 3, 2023 at 19:45
  • Is the vehicle fitted with a water/oil type oil cooler? That is the only other failure that would cause these symptoms. Compression or Leak Down tests required next to confirm. Commented May 4, 2023 at 10:11
  • If the leak is slight you won't get high temperature warnings unless you are loading the engine near its maximum output power, all you'll get is displaced coolant.
    – Stian
    Commented May 4, 2023 at 15:02

3 Answers 3


My rule for blown head gaskets: if you have to ask if it's a blown head gasket, it's a blown head gasket.

There are other ways than the head gasket that combustion gasses could get into the coolant, but for the most part they're just as big a deal to repair as the head gasket replacement, or worse (crack in the head or crack in the block).

Fortunately, the price you've been quoted for head gasket replacement is waaaay too high. Something around $1000 is more reasonable. Shop around, asking for the shop's hourly labor rate before you even mention what the problem is. This will let them know you're not going to be an easy mark for made-up through-the-roof prices. Then, tell them the symptoms, that you suspect it's a blown head gasket, and ask for an estimate for your specific make and model.

Finally, for a Civic, a head gasket is a very doable DIY job, and probably comes in at under $200 in parts. Really the worst (probably the only difficult/high-risk) part is ensuring you restore the cam and crank shaft positions relative to one another when you put the head back on and reinstall the timing belt. Other than that, it's just a lot of disassembly of stuff that's in your way and reassembly once you're done. If you're good with cars but haven't done anything this scale before, I'd allow 2-3 days. With experience you can do it in an afternoon most likely (and this is what the shop should be charging in labor for it).

  1. Given the symptoms, is it a bad head gasket or what else could it be?

It is not conclusive it's a blown head gasket, but realistically, I'm doubting it's anything else ... let's give it a 99.9% probability.

  1. Is the Rocker Arm Oil Control Valve a related problem or something different?

This would be a different issue not related to the coolant. I don't know what specific things have to happen for the ECU to trip this code, but since it hasn't come back on again, I'd suggest it's something to keep an eye out for, but nothing to worry about at the present. IIRC, what you're talking about has to do with the VTEC actuation, so you might try running it up into the VTEC RPM range (I believe that's north of ~4k RPM) to see if it trips again.

  1. Should I not use a coolant system sealer product, because the coolant and oil seem to be mixing?

I highly advise against it. While it may provide a stop to your headgasket leak problems, this stuff has a propensity to cause blockage issues at other parts of the cooling system.

  1. Are there any other problems I'm missing?

I'd suggest your issue with the vents only blowing hot on the left, medium in the middle, and cold on the right, is a product of a bad blend door actuator, not a clogged heater core. The blend doors allow for a temperature separation between sides. When an actuator goes out, the door doesn't move at all, so the temp output won't change. You could try to change the temps to see where it changes and where it doesn't. The one which doesn't is the one which is bad.

You said there is a milky film on the oil cap, but is the oil milky on the dipstick? If you are not running the car so the engine gets completely warmed up (to include the cooling system), the engine can form the milky substance at the cap. The reason for this is it could actually be just condensation which occurs naturally within the engine during the combustion process. Most of what is is spewed out of the exhaust pipe while the engine is running is water vapor. Some of that gets past the rings and into the crank case. Because the cap is at the top part of the engine, the water vapor makes its way there. If you completely warm your engine during operation, it gets warm enough for this water vapor to evaporate. If you're seeing milkshake on your dipstick, all bets are off and you're leaking coolant into your engine oil. This could be from the head gasket or possibly an oil cooler leak or maybe a couple of other things.

I'm not sure if/when Honda changes things in their engines, but for the 2000-2005 (D17) Civic engines, if the owner put anything other than Honda blue coolant in it, sooner or later the head gasket would go. I ran into this on a 2003 Civic. If Honda was still using the same head gasket style in their 2006 engines, it could have the same problem.


I would start off by verifying how the coolant is being lost. A cooling system pressure test (which you can buy off Amazon if you want to go the DIY route) could flag up a blown radiator or loose/perished hose, which would quite obviously pinpoint the reason for the loss.

If that doesn't flag up anything then a failed head gasket would be the next obvious guess, and of course that can only be verified by replacing the gasket (no, just inspecting the current one is not good enough). Far less likely but still possible would be an oil cooler leak, or at worst a cracked head/block.

The fact that you aren't seeing milky oil on the dipstick would argue against an oil/coolant mixing problem, but you've also confirmed that there appear to be combustion gasses in the cooling system, which is definitely inclining me towards a failed head gasket.

As another answer has noted, there's no way any repair shop that's not trying to scam you, is going to charge northwards of $1,000 for a head gasket replacement. This is one of the most common vehicle issues that they see regularly, it involves a single replacement part (the gasket, or three if you include coolant and oil changes), and it's relatively quick and simple to do (take note of the belt timings, pull the belts, pull the head, replace the gasket, reinstall the head, reinstall the belts and match the timings, replace the fluids). If you do send it to a shop you'll likely be waiting longer for them to get stock of the gasket, than it takes them to do the actual swap.

If you're looking to go the DIY route then you'll need a new gasket, new coolant and oil, and of course a wrench with sockets that fit the various bolts. A torque wrench is highly recommended to tighten the head bolts back to the manufacturer's recommended specification. There are thousands of YouTube videos walking through head gasket replacement, which means there's almost certainly a YouTube video of someone doing it for your very model of vehicle, so if you are unsure at any step of the process you should definitely be able to find a reference of what to do (or not to do).

DON'T EVER USE any "coolant system sealer" products. Oil and coolant are very purposefully kept separated in an engine to prevent damaging it - while these sealant products may stop the worst of the mixing of these fluids, you're still going to be getting coolant in the oil, which is still going to be causing damage. And no matter how well these products may work (or more generally, not work), if vehicle's head gasket is failed it will continue to deteriorate, and at some point in the future you're going to have to replace it anyway. That's most definitely a can you should NOT kick down the road, unless you'd like a possibly blown-up engine.

  • 1
    Actually, you can verify a headgasket without pulling the head off by checking for hydrocarbons in the coolant system. When running normally, a cooling system WILL NOT have hydrocarbons present. There are testers you can use to check for the presence of HCs. A little finicky to use, but they exist. Commented May 3, 2023 at 12:56
  • @Pᴀᴜʟsᴛᴇʀ2 The issue there is the whole "finicky to use" bit, because that often means these testers end up giving a negative result when HCs are actually present. Pulling the head may be a PITA but it's the only way to be 100% certain.
    – Ian Kemp
    Commented May 3, 2023 at 14:31
  • 1
    Again, you'd be incorrect, but I'll let you believe whatever you want to believe. The "finicky" side of these testers is not a false negative, but rather a false positive. That has to do if you get coolant up into the test dye, it can change colors which may be misleading. Finicky means you just have to do it correctly. If done correctly, it is an invaluable (read: cheap) resource which will unequivocally tell you if there are HCs present where they shouldn't be. Commented May 3, 2023 at 17:20
  • Gentlemen, I thank both of you. Commented May 3, 2023 at 19:52

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .