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AlumAseal for honda Head Gasket?

I have a 2003 honda civic. I recently replaced the timing belt and water pump. After a long weekend of wrenching, I forgot to bleed the cooling system properly. The next week I was on a road trip and the car overheated a few times. The overflow tank on the coolant was high (almost to the top), and when I checked the radiator it needed about a half to 3/4 gallon. I filled the radiator back up and didn’t have overheating problems until at the end of the road trip when I slowed down from highway speed to about 40mph. When I got home I replaced the thermostat (this time doing a better job of bleeding), and the next day I got misfire codes.

I took it in to my mechanic and he said he couldn’t see any head gasket leak after doing a couple of tests, changed the Electronic Load Detector and said call him if the check engine light came back on for misfires (all cylinders and random except for #1). It came back on and he recommended to change the upstream O2 sensor (which I had recently changed with Bosch brand) to a Denso brand.

The day after I changed the O2 sensor, the car started hesitating when driving, especially over 40mph, when the check engine light was blinking. Took the car to a different mechanic, who noticed the coolant was low and did another leak down test. He didn’t see and coolant in any of the cylinders, but after replacing the spark plugs he didn’t get any hesitation, but still got a misfire code and said the coolant was low again. So he put some stuff called AlumaSeal in the radiator and said that he thought it was a very small head gasket leak, and this should pretty much be a permanent solution, and that I should leave the stuff in the radiator and not flush it out.

I have a few questions:

  1. Does this sound like a good diagnosis/solution?
  2. Is alumaseal going to be able to fix this problem, or will it make any new problems? Has anyone used this stuff before with permanent results?
  3. Since the hesitation happened the day after changing the O2 sensor, could it be that I need to change the O2 sensor (again)?

Alumaseal is a great radiator stop-leak but NOTHING you dump in the radiator is going to cure a blown head gasket…Since combustion pressure is many, many times coolant pressure, the flow is usually the other way, combustion gasses blow the coolant out the overflow tank…Perhaps you have a failed intake manifold gasket, allowing coolant to be sucked into the engine via that route. The Alumaseal might plug that up for a while…

If the leak is in the intake manifold, you can sometimes plug it up with some IndianHead sealer. You put a little on a fine brush and rev the engine a little while brushing it onto the suspected area. The suction will aid it into the crevice.

I won’t put Alumaseal in my '03 Honda Civic. I had a similar problem and tracked down - finally to simply a loose clamp on the upper radiator hose. The hose had been replace due to a pinhole leak about a year prior.

The pressure test of the cooling system did not show any leak or loss of pressure, at first. It held pressure all afternoon at the shop. The repeated the pressure test the next morning when the car was cold and then a very small leak showed up. Apparently the heat from the motor expanded the plastic fitting enough to show no leak, when cold it contracted and voila a leak.

  1. he did not properly diagnose a headgasket leak. You may have one, but you cannotr know from his diagnosis.
  2. If you do have a headgasket leak, alumaseal is not the answer.

By the way, a headgasket leak between the cylinder(s) and the water jacket generally flows both ways. When combustion happens, it blows hot combustion gasses into the waterjacket, and when the intake stroke happens it draws coolant into the combustion chanber, where it “burns” (becomes vaporized).

What were the results of the leakdown test? Did he determine a headgasket leak, as I suspect?

Nope, it isn’t the O2 sensor. But the root cause was probably the overheating.

Thanks for the input guys.
Caddyman: Is there a way I can test for a bad intake manifold gasket? The main reason for taking the car in was because of the intense hesitation. The mechanic changed the spark plugs first in the shop and said he didn’t feel any throttle problems, and he drove the car all around town for several days. If this stuff keeps the check engine light off should I let sleeping dogs lie?

UncleTurbo: The mechanic ran the pressure test on the car when it was cold. Then he put the stuff in the radiator without my giving the go ahead, so I thought I figured if it was already there, see what it does. Is there any particular reason you wouldn’t use it? I figured if any problems come up in the near future with the heater core/radiator, he would be the #1 suspect and (hopefully) own up to it if its a clog.

The same mountainbike: He said the cooling system kept pressure and he didn’t see any coolant in the cylinder walls. This is the same thing I was told by a different mechanic, who used a camera to look at the cylinder walls. What tests would you preform for a definitive diagnosis?

I was thinking about taking the car to ANOTHER mechanic that I searched for on this website after the car was in the current mechanic. Should I wait for the light to come back on/problems to happen before I stop by?

Yes, let sleeping dogs lie…Any mechanic who can inspect the cylinder-walls with a camera is probably a good one…The hacks just don’t get into that level of diagnosis…But if coolant continues to disappear from the radiator or recovery tank, you really need to find out where it’s going…

I won’t use Alumaseal, or any coolant leak sealer, in my Civic because Honda cooling systems are fussy about coolant used. I figure if Honda didn’t develop it and test it, it might not be compatible with materials used in Honda cooling systems. Such materials include plastics, aluminum, lots of different metal alloys. It might be OK, and it might make a mess. You just don’t know.

My symptom was the coolant container would fill to overflow, but there was no coolant in the radiator when you pulled the radiator cap. If I filled the radiator, it would then overflow the container again. For a few days I was taking fluid out of the coolant overflow container with a siphon and putting it back into the radiator via the radiator cap opening. This went on for several days and the coolant was not being drawn back into the overflow container meaning air was getting into the system somewhere and killing the vacuum pressure that is created when the motor cools down. So, if you are pushing fluid into the overflow container and not getting it pulled back in the motor after it cools you have a leak somewhere allowing air to get into the system. My leak was very small and right where the upper hose clamps to the radiator, tightened the clamp and back to normal.

I had to depart for a moment, but I’ve returned. You can sometimes find a difficult leak using an additive to the coolant that glows under blacklight, called a UV sensitive dye. It’s available at any parts store.

Problem solved for the misfire: it was a head gasket. I flushed the alumaseal out after replacing the gasket, so I am not sure how much help/damage it did.

On the diagnosis of the head gasket: I took the car to 3 mechanics. One said it definitely wasn’t the HG because a compression and leak-down test showed nothing. The other said it was the HG, but based that on the idea that “coolant is going somewhere, and its not on the floor of the shop,” which wasn’t proof enough for me to do such a large job. The last mechanic said the valves were out of adjustment. They were, but not enough to cause misfire.

In case you are having the same problems i was: The determining test was a cylinder leak down test, which I did by just running the engine

Top off your radiator (with the engine cold) and turn the engine on with the radiator cap off. I ran the car for a while and watched the fluid ebb down the radiator and overflow out, topping off every time it ebbed out with water. I noticed that bubbles kept coming out, smaller than when you normally bleed the cooling system. There are youtube videos that show it. You can also ask your mechanic to do a cylinder leak down test, or buy the kit on amazon for $50 and DIY, and get the same results.

After I got the head off, it was obvious there was a leak between the cylinder jacket and cylinder on #4. I also noticed after driving the car ~50 miles on the highway that not only was coolant disappearing rapidly, but that there was some gritty brown stuff on the underside of the radiator cap, and when I drained the coolant, there was a lot of brown to it. If the bubbles in the radiator and disappearing coolant didn’t point to the HG, the brown coolant told me I wasn’t wasting my time taking the heads off.

It was kind of grating that the 2nd mechanic was right, and could have saved me a headache for 2 weeks and $100 for the valve adjustment had I listened to him. The problem was, I am not going to take the car apart because coolant is disappearing and the mechanic figures points of loss must be in the engine if its not dripping on the floor… A HG job is a little too much of a PITA to be a shot in the dark.

Head gasket leaks can be quickly verified by sniffing the gasses in the radiator for any trace of hydrocarbons. Many shops are equipped with sniffer tools designed for this purpose. The old tailpipe emissions testers can be used for this too…Another even simpler method is to attach a radiator pressure tester to the filler neck and rev the engine while you watch the needle on the pressure tester. If the needle jumps when you goose the engine, you know the head gasket is blown…

Thanks sincerely for the follow up post, as well as the recommendations. I’m glad the story had a happpy ending.

Happy motoring.

Some of the methodogy used sounds a bit strange to me but hopefully the problem is solved for the long term.

I would hope that you checked the cylinder head for flatness while it was off. If it’s warped then it could come back to bite you again later on.
There could also possibly be an issue with the valve adjustment if some of them were too tight and especially so if it involved exhaust valves. This is also something that can rear its ugly head in the future.