Vapor Lock

R

rfitzpatrick

Well-known member
My The Restorer magazine has this about a vapor lock question:



"Others Add A Pint Of Marvel Mystery Oil To A Tank Full Of Gasoline, Which Raises The Evaporation Temperature Of The Fuel".


Any thoughts -- I'm glad to read about this
Thanks
 
Fuel is a mixture of many different hydrocarbons, each with e different boiling point. Vapour lock is caused when the fuel boils and the vapour causes the fuel to not flow. IMO, adding MMO will not affect the boiling point of the more volatile hydrocarbons, just slightly raise the average boiling point
While some may have experienced otherwise, I cannot see how adding MMO would have much, if any affect.
Not that we even have MMO!
 
MMO has no affect on the boiling point of gasoline. I'm sure MMO appreciates the spreading of this info, it does help their bottomline. If you want to add a pint, add a pint of beer, it costs the same, is just as effective on vapor locking, but tastes a lot better than MMO.

You're better off finding gas without ethanol, it's out there.
 
rfitzpatrick said:
My The Restorer magazine has this about a vapor lock question:



"Others Add A Pint Of Marvel Mystery Oil To A Tank Full Of Gasoline, Which Raises The Evaporation Temperature Of The Fuel".


Any thoughts -- I'm glad to read about this
Thanks
Click to expand...

Whatever the chemistry is, MMO works.
 
Just the name of the product is intriguing. My good friend and Model A owner (Roger Withers RIP) swore by the stuff - more for value lubrication as I remember.



Anyway, I still have half a bottle still sitting on my shelf.
 
I used to have vapor lock once in a while and some old model A mechanics said put a couple clothes pins on the gas line close to the carb. Did that and haven't been bothered with vapor lock since. That's been over 8 years ago, don't know if that was what fixed the problem but haven't had vapor lock anymore.
 
Gasoline formulation changes for summer and winter. If you have winter gasoline in your tank, which is more volatile, and driving the car in warmer weather, try draining that fuel to put in your modern car and adding a tank of summer gasoline.

Hi engine bay temperature will increase the tendency to have vapor lock. Some people have reported that adding the engine pans back keeps the engine bay cooler and helps with the vapor lock.
 
'Vapor lock' does not really exist in the A. Yes, I know that you can get the fuel in the carb bowl bubbling these days because of the boiling points of parts of gas. That is not vapor lock and should not affect driving. It will show up during engine shut down heat soak or may be a parade.

I will use logic and facts, not opinions. Consider these points.

A group of cars experiencing the same conditions and similar gas. That is fuel from one region and the same time frame. A car or two will have a 'vapor lock' condition. If it were the fuel then all would have issues.

Often it is the same cars having the same problems. Often it is at some edge of conditions too.

Which brings me to what is the real problem.

A problem in how the engine was built. When an engine is built with less care or understanding you can accidentally make one or more conditions that might just be at and edge of being and issue. Worse is when you have several items at an edge and you need all conditions right to cause a problem.

These are very hard to diagnose. So it is just easier to think it is just some vapor lock issue.

The problems come in many varieties. Here are two areas that are likely more common. I do not have data to say for fact.
First is a car where timing, recessed valves or carb issues cause the engine to run hot. Maybe coupled with a poorly cleaned block and a marginal radiator. This causes the fuel to boil.
Then there can be issues where valve lash was done just a slight be tight. A couple of cylinders just never have their valves close sometimes when a mix of temps are right. This one was told to me by a guy who used to believe in vapor lock. Then he needed to take the engine apart for other reasons and checked the valves and found them not quite right. Never had vapor lock after that.

The moral of the story.
The Model A engine will just run if it is built with care following factory build tolerances. If keeps stopping for some reason it is because something is not right and not some mythical vapor lock. Are your valves done right, is your carb with proper sized jets, have you truly cleaned the block, does your radiator actually flow water and so on down the list. It is not cheap or easy to get the Model A running properly. It is really like building a race car engine.
 
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