After my Honda CB500 was (mis)diagnosed to suffer from a blown headgasket, I trawled the net looking for more information on the topic.

What’s a headgasket

The headgasket is the seal between the cylinder head and the engine block. It ensures the pressure stays inside the cylinder(s), coolant stays inside the water sleeve (and doesn’t seep into the cylinders).

Symptoms of Headgasket problems (”blown headgasket”)

1. Loss of power - because compression from the cylinder(s) is escaping due to a leak of the headgasket.

2. Coolant can leak into the cylinders and evaporate inside or mix with the engine oil.

3. Mixing fluids (coolant and oil) causing either fluid to look contaminated (milky).

4. Compression from the cylinder may escape into the coolant system, causing coolant to bubble and gush out of the overflow tank.

5. Reducing coolant levels will cause the engine to overheat, which may seize the piston and cause further damage.

6. Excessive white smoke coming from the exhaust (caused by coolant evaporating inside the engine), damaging the catalytic converter (if your vehicle has one).

When your headgasket is damaged, it may be that you do not instantly notice a difference in how the vehicle drives. It could run like normal (but leaving behind clouds of white smoke) until all the coolant has gone and the engine overheats.

Repair

Depending on what type of vehicle you have (how much it’s worth to you!) there are two ways of countering a headgasket failure. Either take it to a mechanic and have the headgasket replaced (or if you feel up to it, replace it yourself). This could be quite costly, which may or may not be worth it considering the value of the vehicle.

You may also want to try a less conventional method; Steel Seal. It’s a liquid which you pour into your radiator. It then moves around and (hopefully) seals the damage on the gasket to make it “as new”. Now I haven’t used this, so can only go by people’s opinions in various forum posts and reviews. The crowd is divided. Some people say it’s crap, and some say it’s brilliant. But it’s not that expensive so you might want to try it out before shelling out hundreds of pounds replacing the headgasket….

Prevention

There is no way to prevent your headgasket from blowing. As the engine gets older, the seal may become weak and just give up after a while. All you can do is pay attention to what your vehicle is doing (is excessive white smoke coming out of the exhaust?) and try to limit the damage to just the head gasket rather than driving around until your engine overheats and causes all sorts of additional problems!

Unfortunately my CB500 respray project has been on hold for the past couple of weeks. I’ve had nothing but trouble with the bike on the daily (modest) run to work. 

Symptoms: Perfect running until for no apparent reason the bike gets jerky, loses power, revs fall, and just acts as if it’s run out of petrol. Upon pulling over it would stall, and refuse to start for the next 3-4 minutes or so. After it does start again, upon revving it will backfire once or twice and continue to run perfectly until everything starts all over again….

So what does a girl do? Getting sick and tired of having the bike die on me in the midst of rush hour traffic up to three times in a 1.5 mile trip to work, I decided to drop the bike with a mechanic. Picking a “proper shop” nearby, I explained the problem and hoped for the best. Then I remembered that sometimes (every few months or so) the bike tends to overheat and spit out coolant. That little bit of extra information pretty much distracted the mechanic from then on - insisting that both problems MUST be related.

A phonecall a few hours later spelled trouble. The mechanic said he had a look around the cooling system of the bike and found that the coolant level was extremely low. He then tested the fan (which worked) and ran the bike a little. To his horror coolant gushed out of the bike as soon as the engine ran for a minute or so, not enough to make it hot!

His diagnosis: blown head gasket or cylinder ring. He told me he’d do a compression test.

Result: left cylinder: 175psi, right cylinder: 125psi. He was even more sure now that it was a major engine problem causing all my trouble… Quoting me a grand for all the work to put it right, I was totally horrified obviously (especially since the bike had cost me less than that in the first place!) so I decided to take it back as it was.

Mechanic #2. Luckily, there’s this other mechanic close to where I work who helped me out on previous occasions (see: Replacement Spark Plugs) I gave the bike to him, explaining what the other mechanic had said (blown headgasket - repair: 1000 bucks) and although the repair cost gave him a good laugh (and he quoted me about 350 for the same thing) he promised to have a good look around the bike to see what was up.

A few hours and phone calls later: he claimed the bike ran beautifully, and after having it on for a while, coolant stopped leaking out, making him suspect that it had been overfilled. It couldn’t possibly be anything as serious as the headgasket then… 

As my husband and I had suspected from the beginning of this whole ordeal, I told him maybe the tank and carbs are dirty. I asked him to strip the carbs and clean out the tank and see what he finds inside. He was happy to oblige. Indeed I get a cheerful phonecall that evening detailing how he’d found “a load of shit inside the carbs and tank” and the bike was still running beautifully. 

Yay! I got it back last night, drove it around til it overheated and spat coolant out again.. but it didn’t stop even once! Sure I know I should have the radiator fan looked at (It doesn’t cut in even when you could use the engine for a stove), but hey, from home to work it won’t even get luke warm. At the moment (having spent what I have just now on two separate mechanics’ fees) I think I’ve bought myself some time.

Morale of the story: 

1. Before paying a mechanic a grand to work on your old vehicle, take a second opinion!

2. If the bike feels like it’s not getting any fuel, it might just be as simple as it literally not getting any fuel.

3. Older bikes might have rust in the tank which might eventually cause running problems. 

For more information on headgasket problems, see my next post “Headgasket Woes”.