VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 vapor lock and possible solutions

Next week, we will be taking our 32 Special Sedan on the AACA Founders Tour. The weather is t be hot and humid. Is there any additives or solutions techniques to help reduce vapor lock? I do have an electric fuel pump ( with a cutoff switch and I mostly don't use it).

Someone told me that Marvel Mystery oil helps reduce vapor locking. The engine is rebuilt and runs well.

Just short of sitting on the side of the road ( or at a stop) and waiting - any suggestions?

Tom

Get some REAL gas instead of Ethanol and that will help considerably.

Take a gallon jug of water along to pour over the fuel pump so if you do have vapor lock you can get going faster.
If you have a properly mounted eletric fuel pump you shouldn't have a problem.

Add 10-15% diesel to the fuel in your tank. It is easy to do at stations that sell diesel. Will not cause any problems but does increase boiling point or reduce vapor pressure of the fuel mixture.

I try to find 100 gasoline but that is tough. What about kerosene rather than diesel? Have you tried that? diesel or kerosene?

I didn't think about the water on the pump - another good idea.

Diesel works and is easy to find. Kerosene is not nearly as available. It also will decrease the vapor pressure as well.

Diesel will reduce the volatility of gas and helps but you've got the solution with the fuel electric fuel pump. Motor On. .

If you have an airport nearby, they usually have high octane (100 or so) low lead gas for the piston engines. works great when I mixed 5 gal into a 25 gal tank of the '79 1 ton dually. cost is a bit high, but it's either that, premium w/o corn, or trying to find someone that sells turbo blue/racing fuel...also a bit pricy. the Aviation stuff has a nicer smell to it than unleaded. Not sure though if I would mix 100% of it for the old car. the original manual says I think 98 hp using 75 octane leaded fuel.

In the heat of summer, I use 10% diesel fuel....No vapor lock...I just keep a small tank and short fuel our 32, then drive home and put the diesel in. In SC, non-corn fuel was easy to find. Here in Va., almost impossible!!!!

Mac

Could someone here explain how to determine if you have a vapor lock condition vs. some other condition ? Can it happen while underway or mostly after the engine is shut down and unable to be re-started ?

In my case, it has happened after engine shutdown and the fuel percolates causing air bubbles to form in the fuel bowl and line. Will not start until it cools down. I haven't had the problem in a few years...

It can happen underway and when attempting to restart. Symptoms are hesitation on acceleration, a slow loss of power, followed by missing and in extreme cases stalling.This, on a hot day with an otherwise good running engine on a long, or hard pull. Also during an extended run in extreme heat. Long periods of idling in creep and beep traffic can also cause it

The hard start after stopping is caused by the gas percolating in the carb creating vapor and peculation in the pump. The carb sits on the hot side of the engine and there is large amount of heat build up from the exhaust manifold, radiator and the block when the engine is stopped and there is no air flow. The hot air is trapped under the hood. A tight fuel delivery system and a good pump go a long way in preventing vapor lock. Any air that gets into the pump can cause cavatating and bubbling creating vapor lock. Pump can't pump vapor.

Tony

Thanks for the thorough explanation. I suspected vapor lock a couple times last summer when I had to wait 30 minutes or so to get her going again. I thought it might have been the coil. Someone told me to try wrapping the carb in insulation beforehand…or wait for cooler weather.

The vapor lock occurs in the fuel pump which picks up heat from the engine block.
Some makes of cars in the '30's and '40's used a deflector to direct cool air to the fuel pump.

Well, an update of conditions and observations. Conditions were tougher - daytime temperatures were 90 to about 93 with humidity varying. The tour did not have excessive long runs ( >30 miles at a clip) and only several fairly long hills ( 5% grade for about 1 mile).

On day one after a long climb, the Chevy started to vapor lock and the use of the electric fuel fixed the solution but as soon as I cleared the vapor locking, I then turned off the pump.. I did have some increased temperature but not severe over-heating.

That afternoon I added about a 5% addition of diesel - ( temps about 92), I did have some difficulty starting the hot engine ' hot start' then carburetor vaporization?

After diesel addition, and the next morning especially, the car was a little harder to start. I have NOT yet examined spark plugs.



Day 2 - higher temps by a degree and one instance of vapor lock - with ~5% diesel AND cleared by use of electric pump. Strange. Continued harder starting or rather slower starting - typically, it fires on the first few revolutions of starter. Increased diesel to ~7%.



After ~7%, starting was a little 'harder'..... So decided next iteration was back to 5%. During the heat of the day, the car was hard to start - it would fire on a cylinder or two then require chiocking to get it to start and it was almost always irregular - not all cylinders firing then cleared to all cylinders firing in 10-12 seconds.



Observed another car using 10% diesel - and significant exhaust smoke. Friends told me they did not see smoke at any time from 5-7 to maybe 3ish%.



By day four, I was really tapering off the diesel addition shooting for 3-4ish% I just was getting frustrated with the harder starting.



Additional measures after any run then tour stop was to open hood to aid cooling AND pour a little water on the fuel pump. Starting was always hard so I started to pour a little water on the fuel line to carburetor ( I have it insulated and assumed that the water-soaking would result in transpirational cooling - alas, still hard start). Almost AWLAYS needed to choke it AND use about 1/4 foot throttle to start. Almost ALWAYS fired irregularly but cleared after 7-10 seconds to consistent cylinder firing. Then idled fine and ran OK. With the higher percentage diesel in the morning with a cool engine, it seemed to have a periodic misfire that disappeared after about 5 minutes, medium to high throttle and then warm engine.



Some suggestions from some folks on the tour: change the line from copper to SS. polish the copper entering the pump ( better reflection? lower emissivity?), add more insulation, go to 10% diesel.



Use of the electric pump all the time seems to flood the engine after I stop ( especially after running for some time) I can hear the electric pump running and then it sounds like ( after say 7 seconds) to start to dead-head.



I think the car needs re-tuned to run the diesel addition - but how?. It generally does seem to help but the slower starting is a problem and confusing - any thoughts?

Strange that you had harder starting with the 5-7% added diesel. I never noticed a difference in starting even on colder mornings. Might check the spark plugs to see if they are carboned. Never had a problem with that even when running 0.025" and 12 deg.

If you are running Ethanol gas that could be part of the problem.

There is Ethanol addition to almost all the fuel I had/have access to. IN Pennsylvania, The federal government standard during summer months is a RVP ( Reid Vapor Pressure) of 7.8 versus a winter blend of 9.0. This formulation means that summer blends are 'harder' to vaporize than winter blends.( high VP - high vaporization, low VP - low vaporization) Since ethanol vapor pressure is consistent and it's amount ( 10%) is the same summer to winter, that implies the gasoline portion is 'different'.

I'm wondering is there was some kind of 'heat soaking' in the carburetor simply due to its elevation in the engine compartment - that is why the car seemed hard to start - maybe. But it was hard to start even after sitting all night long - I haven't looked at the plugs yet. I had done a compression test a while back and all cylinder were fine ( recently rebuilt). Oil pressure was always good. Weird.

I plan on trying kerosene - which in the US is usually available at stations. Kerosene is considered #1 diesel - it is more refined and I believe a higher HHV than truck/tractor/home heating fuel - which is #2 diesel. In the US, there is change over to ULSD ( Ultra Low Sulfur Diesel)

tom, this is what happened to me: i had a true work truck in 1974 in sacramento, ca.. hot as the devil. so, while hauling scrap metal loads, the old '53 chev (216) 1/2 ton really worked up a sweat. by mid afternoon,vaporlock vaporlock vaporlock. my father in law says to put a cloths pin on the fuel line as it nears the carb. i wagged my young head and thought "such foolishness". later, out of all ready options, i did it, except i went for it and put several on the line. results: no more vaporlock, ever, swear to god. maybe the wooden fins dissipate the heat, who knows. he's now a few weeks from 91 and he do know a thing or two. i hope this helps. jim ('30 coupe)

the chevy six clatter means nothings the matter.