L-79 overheating and no-fire

[Tom Merkel]

Here's what happened several weeks ago. Could I get some opinions on what might have been going on?

My '67 L-79 was caught up in some traffic. It was 85 degs.+, and no air to speak of. I decided to let it idle after sitting several minutes of not knowing what was up ahead. Little by little, the temp gauge rose to 210+. By then, I knew either I needed to get going again, or shut it down. What should I do? So, I left it run a little more, and eventually turned it off, 'cause the traffic wasn't budging.

Finally, traffic opened up in about five minutes or so, and I cranked it. Healthy crank, turned over well, but nary a hint of firing up. More crank, still no fire. Finally, I pulled it over (on a slight down-grade) and popped the hood. Let it cool down for about an hour, then cranked it. Fired instantly, temp was down to 180 or so.

Anyhow, what was going on? Vapor lock? If so, can it be prevented. By the way, it's never done this before.

Thanks for input.

Tom

[Wayne K.]

Re: L-79 overheating and no-fire

Tom,

One possible cause could be heat soak. When you shut it down heat soak caused the carb to boil over flooding the engine. When you cranked it 5 minutes later you had ignition but did not fire because of the flooded condition. By waiting you gave it a chance to clear up.

[Bill Clupper]

Re: L-79 overheating and no-fire

Probably vapor lock, likley cause- bad fan clutch causing overheating. With good fan clutch, should be able to idle in 85 degree temp "forever"

[Tom Merkel]

Re: L-79 overheating and no-fire

Bad fan clutch is evident by (1) seeing if it spins?, (2) or only by experiencing over-heating?

I know it 'turns', but is there a metric to use to determine if it 'spins' up-to-spec?

Thanks.

Tom

[Bill Clupper]

Re: L-79 overheating and no-fire

Not a reliable one that I have found. An easy check is to purchase an aftermarket fan clutch and do the idle test. If it solves the heat problem, have the original rebuilt. With the engine hot, there should be a noticable "Wash" of air coming out of the fan shroud when you rev the engine.

[Doug Flaten]

Re: L-79 overheating and no-fire

I have had similar symptoms when the capacitor on the points went bad. Engine cranks etc but will not fire until the capacitor cools back down. Then it may drive a while until it heats up again. I'll show my ignorance and state I do not know what ignition system is in a 1967. But if you are running a points and capacitor, the capacitor may be a cheap fix.