Is it possible for a blown head gasket, something akin to a brain aneurysm, to heal spontaneously?
If not, was the gasket in fact blown?
And if not, whence the coolant leak?
So many questions. For the time being no satisfactory answer.
Here are the facts as I know them. I need your insight.
After a long day’s ride from State College to Niagara falls, some 370 kilometers, a coolant leak in the engine compartment brought the day’s ride to an abrupt end.
It was impossible to see the source of the leak. The coolant was running down onto the center stand pivot or axle and dripping from there. You can see this symptom in the video I posted as episode 22 of the vlog.
Other symptoms: when I opened the saddle to refuel, steam was rising from the engine compartment. When I removed the underseat bucket to reveal the engine, there was coolant everywhere, as if there was a spraying coolant leak. The underside of the seat compartment bucket was wet. When I started the bike with the bucket out, the coolant was dripping from the stand below the motor, but there was no evidence of a leak seen from above the engine.
That’s all I’ve got.
Last week I needed to get my bike down from its P1 parking spot to a temporary spot on P3 because the P1 level was being pressure washed.
I refilled the cooling system with tap water, up to the lower fill mark on the reservoir. I fully expected to see the water begin dripping down the stand. But there was no leak. I started the motor. Still no leak. I left the motor running until the bike reached normal operating temperature. Still no leak.
I rode down to P3. Still no leak.
Two days later I checked on the bike before riding back up to P1. Yup, still dry.
I discussed the situation with Ed Thomas. Ed thought that perhaps the water was leaking into the oil pan via the blown gasket rather than leaking to the outside. He suggested checking the coolant level in the reservoir, and checking the oil level. If both were at their normal levels, it would be reasonable to conclude that the coolant wasn’t leaking into the oil. I checked and the levels were normal.
Today I decided I would hop on the Vespa to run a few errands and eventually make my way over to Ed’s workshop, to talk, well... talk shop, and zombie Vespas. You guessed it, still no evidence of any leak. That, and I kept an eagle-eye on the instrument panel: the engine temperature remained normal the whole way. The check engine light lit up a couple of times, but reset itself with an engine restart. That happened three times on the way to Ed’s, each time shortly after one of my little errand stops. It never happened on the way home.
Ed’s as stumped as I am.
The only other thing I can think of, is that close to the Pennsylvania New York border, I refueled at a tiny country gas station, and I realized that the helpful attendant handed me a nozzle switched to regular gasoline with ethanol. I only realized it had happened further down the road when the engine started stumbling slightly. Three tanks of 91 octane fuel later, the performance symptoms disappeared. I don’t think that’s relevant. I just mention it because it’s the only other engine-related issue that occured on the trip.
So there you have it. The Vespa seems for all the world to be running like a top. Or at least running as well as it did when I set out for the wilds of Pennsylvania.
I know many of my readers have what I’ll call mechanical literacy. What is your take on this little Italian mystery?
Is there any chance that the coolant leak might have come from the coolant bleed valve at the top of the engine?
Can a blown gasket heal itself?
Should I overhaul the engine on the assumption that there is a defective gasket?
What would you do?
Like I said, I am stumped.
Thanks for reading.
PS: I also posted this mystery to the ModernVespa forum: here’s a link.
PPS:
In this shot taken from the Episode 22 video, filmed within 15 to 20 minutes of the discovery of the leak:
- The circle is the thermostat housing and the nubby thing in the circle at the twelve o'clock position is the coolant bleed valve.
- The arrows point to the areas that are wet as a result of the leak.
- Remember that the pet carrier / underseat container was in place when the leak was leaking. It seems consistent with a leak from the thermostat that the wet areas are aft of the thermostat.
- The areas forward from the thermostat are dry.
- Whatever that evidence points to, it is not really consistent with a head gasket leak, or so it seems to me.
Another MV'er (whom I believe to be another mechanically literate person) had this to say: "It is very rare to have an external coolant leak turn out to be a head gasket. It would usually go into the engine oil or out the exhaust."
Yet another MV commenter had this to say: "Hmm. Not clear whether you mean the gasket at the base of the cylinder (possible) or the one which seals the two halves of the crankcase (unlikely). You don't develop anywhere near as much pressure in the crankcase and spraying coolant all over does not seem likely to me. You would lose engine oil if anything. I think the thermostat/bleed valve area sounds far more likely as you suggest. Probably time for a trip back to Vespa Toronto West for reconsideration."
