Vapor (Vapour) Lock

[Minnhawk]

Well, my WC-56 usually waits until the heat of the 4th of July Parade to vapor lock, but I guess it has moved up the timetable......on our Red Bull convoy was this past weekend. After running on a two lane highway for 3 miles @ 40mph, as I turned off onto the county road, the engine died. Engine temp was normal, but the air temperature must have been around 92 degrees (F) and humid. (thought I was back in Missouri) It would not start back up despite some healthy cranking. I was in a "panic" because both of the M-35 drivers behind me immediately offered to tow me to the next stop point. (visions of my command car swinging like a pendulum behind either of the behemoths terrified me).

I had a "flashback" to 1964- southern Utah on a family vacation up in the low mountains. Our '60 Mercury had vapor locked. Dad gets out and grabs the thermos water jug (remember those days?) and dribbles cold water on the carb bowl and fuel line. The old merc fired back up just fine. So, there I stand with a dripping bottle of Aquafina in my hand, staring at the carb and fuel line. Should I or shouldn't I? Winching, I gingerly dabbled water on them, cringing at the water hissing off of the exhaust manifold. Boom, the WC fired right off. One of the M-35 owners, obviously disappointed, told me that if I didn't mind a few scratches, I should fold the lower hood up under the top hood to help air flow. Not a problem the rest of the day.


The heat shield is on above the fuel pump, and the Brit I bought the WC from had wrapped the fuel line with what I would call asbestos rope (perish the thought that I imported a know carcinogen back to the US).

Well, at least a jeep and another Dodge also had vaporlock problems, although the owners "passed" on the water dribble technique.

Has anyone else tried the water trick? Is it a proven method or was my revered WWII Veteran father totally nutz?

[Tony B]

We stalwart British learn such tricks from running Bedford OY trucks (Oh Y won't the ****** thing go this time?) It has been known for rags soaked in puddles to be used. I've heard all sorts of reasons and answers about gassing. The two I seem to have had succes with is clean carb and check mix, check timing. If the mix is weak or timing retarded it can generate extra heat. what do you use in the rad? I always run a 50/50 mix of antifreeze and never (Touch wood) had overheat problems.

[Dodge-yes]

The problems with vapor lock commonly occurs on Dodge's. I''ve had my share of stops during the summer months. Dousing the carb and fuel line with water has been one way of trying to combat the problem. I finally solved it by re-routing a (longer) fuelpipe in a curve away from the heat of the exhaustpipe.

I heard from one of the 1950's US car guys here in Sweden that covering the fuelpipe with asbetos actually aggravates the problem...

Later
Goran Noren
Sweden

Brazilian Expeditionary Force, Italy, 1944-45
1944 Dodge WC51 ambulance
Ch# 81741448

[John in Washington State]

I have a Zenth 29 and have the heat shield on the engine. I have not had any problem when our weather is upper 90 degrees.

[Ray]

An inline electric fuel pump will fix the problem,also try some diesel mixed with the petrol ,i have heard that this fixes vapour lock problems Regards Ray

[Ugg]

Ray:

Ya need to figure out how to log in. I know they say ya can't teach old dogs new tricks, but I found that ain't true either.

Later

[mazungumagic]

I had the same problem a couple of years ago when I was returning from a car show in my WC55/52. Temp was around 42 degrees centigrade (fahrenheit = bloody hot).

The engine died completely and I had to wait for it to cool before being able to kangaroo hop all the way home.

Fixed the problem by inserting an electric fuel pump just forward of the tank on the right hand side and routing a new fuel pipe down the right side of the chassis rail to the carby.

A cooler solution.


Jack

[G. Miskovsky]

Have had no problem with mine running the Carter carb on it, can't you push fuel back into the bowl using the fuel pump hand lever, rather than put an electric pump on?

[Lang]

There has been a long, involved thread on this subject on the MLU forum particularly related to Ford CMP vehicles but touching Dodges and Chevrolets also.

The problem with vapour locks is basically caused by fuel reaching a heat where it becomes gas instead of liquid. This problem is all in the fuel pump not lines from the pump to the carb.

The most common time vapour lock happens is on restart when the vehicle has been switched off for a short time after a run and heat soak from the engine heats the pump to such a point that the fuel starts to vapourise and the pump valves which work OK on liquid are not good enough to pump gas so it starts to "wheelspin".

The pump normally is kept cool enough by the air flow from the fan (Heat shield not only protects from manifold radiation but directs air over the pump) and the cool fuel passing through. On very hot days or crawling along in a parade, a pump which is a little down on efficiency can reach a temperature where it starts fail to pump the vapourising fuel.

There are a number of ways of fixing this.

1. Make sure your pump is up to new specifications by replacing or rekitting.

2. Make sure all your filters are completely clean and free-flowing as a pump struggling with "bubbling" fuel will not provide as much suction and the resistance of dirty filters could make the difference.

3. Blow back through the line to the tank. You might have clean filters but an unseen partial blockage might be the culprit.

4. Make sure all unions are tight. Go around and give them a nip up as it is very hard to check leaks on suction lines and any air will enter before the fuel and wreck the suction.

Another common fault is the old "rubber" tip float needles. Modern fuel kills the rubber making it sticky and it can jam in its seat when the carb gets hot, say after a short stop. This fault can also manifest itself as flooding when the sticky seat fails to seal properly. people may think the vehicle is vapour-locking when in fact it is flooding. Replace the needle and seat with an all-metal kit.

Fuel with ethanol in it vapourises at a much lower temperature than normal petrol. Avoid this like the plague (hard to do in some countries where they add ethanol during winter)

If you are near an airport use AVGAS 100LL. Not much dearer than car fuel these days. The vapour point of AVGAS is way higher than car fuel and it will stay liquid long after normal fuel has turned to gas. A BIG plus for old car users is the fact it has around 16 times more lead in it than modern car fuel - absolutely perfect to save our old valves designed for leaded fuel.

Chevrolet and Ford (which suffer much more from vapourising than Dodges or Chevs due to the higher pump position - requiring more lift -and placinement on top of the hot engine) were aware their pumps were not good enough in all circumstances and fitted additional electric pumps for vehicles going to India/Burma

Instant practical permanent fix: Buy a small electric in-line fuel pump from any car parts place. Place this in the line along the chassis as near as possible to the tank (pumps can push much more than they can lift). Also fit a plastic in-line filter which cleans the fuel vastly more efficiently than the military filter, can be viewed for rubbish as they are clear and can be replaced in two minutes by new ones costing a few dollars.

A big plus for the electric pump is the fact it will prime the carb after a long period of no use saving lots of hand priming or flattening batteries by cranking over to get fuel up to the carb. No matter how hot the fuel gets the pump will continue to push solid fuel through the mechanical pump and up the lines to the fuel bowl. The vapourised fuel will just bubble through the needle and either return to liquid in the bowl or vent to air while the float acts normally only to whatever liquid is coming through which will continue to be pushed by the electric pump until the needle says enough!


Lang