After reinstalling the mechanical fuel pump in June that I just had rebuilt and taking my electric fuel pump out that I had been using since 1988, I discovered that my car would now vapor lock in hot weather. This would happen after a short shutdown and while in heavy traffic. Pouring water on the fuel pump would allow the engine to restart.

My original plan was to use the electric fuel pump to prime the mechanical one during starting and this would require my Carter P4070 electric pump to have a bypass with a check valve. With the vapor lock happening in traffic, I've decided to remove the mechanical pump and put the electric pump back in service for the time-being.

SSDan has a fuel line reroute mod but I don't think this would be very effective in my situation. How does everyone else deal with their vapor lock situations?

I've got a writeup about what I've learned here: Vapor Lock

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

i would run the electric pump with a return style fuel regulator along with with a return line back to the tank.

In my case I am doing an EFI conversion. I got so frustrated with the last tank of "winter blend" fuel, I decided to bite the bullet and convert.

Is the engine running really hot? I have never had a vapor lock problem in any Slant 6 vehicle, stock or otherwise. Maybe the stock pump is defective or the cam eccentric is worn down? We had that (cam) happen on the Lemons racecar and it took us forever to figure it out.

Lou

_________________
Home of Slant6-powered fun machines

Frank, does the metal fuel line between pump and carburetor follow factory routing? I found that encasing that line in plastic wire loom, that corrugated black plastic stuff with a slit along its length, seems to prevent any vapor lock. While braking in my newly rebuilt engine that ran firecracker hot for the first 100 miles, and would drive temp gauge all the way east during a short heat soak shut-down, engine would fire right back up.

It's a low buck no tool fast option to try.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I have a 195° thermostat with a V8 rad and my car doesn't run hot. I don't expect that the cam eccentric is worn since I removed the mechanical pump in 1988 and have been using an electric pump until this year. The mechanical pump was rebuilt by Then & Now Automotive this year before being reinstalled.

I installed the electric pump because I thought I was having a fuel delivery problem at the dragstrip. The electric pump didn't make any difference because the problem was actually due to an incorrect transmission throttle pressure adjustment. I continued using the electric pump because I didn't feel like putting the mechanical pump back in. Over the years, I never experienced any fuel-related issues with the electric pump but would occasionally have a slightly worse idle in hot weather heavy traffic - presumably because of some minor percolation in the carburetor or fuel line. I think the heat dissipator gaskets (Mr Gasket 98A) work fairly well because the gas in my carburetor still hasn't evaporated (just checked the accelerator pump squirters) after my last hot weather drive when I was experiencing vapor lock.

The reason I believe that my problem lately was vapor lock in the fuel pump is because there was no fuel in the carburetor after several minutes of cranking and the mechanical pump was too hot to touch. I could easily restart the car and continue on my way after pouring water over the fuel pump. If the problem was percolating gasoline in the fuel line between the fuel pump and the carburetor, I would expect that a hot fuel line would manifest itself more in terms of rich poor idle because the vapor should continuously purge from the fuel line with flow into the carburetor.

My fuel line follows the OEM routing from the pump across the front of the engine to the carburetor. I also thought some thermal shielding would be a good idea and was planning to add some 3/8" split flex wire loom. The 5/16" split flex wire loom grips the steel tube tightly and I think the air gap with the larger loom would work better.

See YouTube: Glass Fuel Filter Vapor Lock Chevy 350

For those of you still using mechanical pumps with clear fuel filters, does your fuel filter show more fuel content if you run water over the fuel pump at idle?

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

Frank,

I also run a 195* stat, stock mechanical fuel pump, stock six cylinder radiator and have been able to start engine after heat soak driving temp gauge all the way east with five or less seconds of cranking. My car is a 67 perhaps there is more air flow in and around fuel pump area with the "wide body" cars. I do have Clifford headers (no heat wrap) with Holley 390 perched on top of Clifford 4V short intake. Maybe that setup keeps enough air circulating preventing vapor problems. One other thing, I have replaced both cowl and front header hood gaskets which cause hot air to move down under car.

I'll take a few temperature readings of various parts of fuel system for you to compare some time today; high temps predicted to be 86* F which sugars out to 29.4 Canadian degrees LOL

Bill

_________________
67' Dart GT Convertible; the old Chrysler Corp.

82' LeBaron Convertible; the new Chrysler Corp

07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Frank,

I went on a 15 mile ride rolling hills two lane road 40 to 55 mph, got her good and warmed up, temp gauge pointing to right leg of "M", and parked. Immediately while engine idled @ 700 rpm in driveway then took temperature readings. All of engine and parts painted black except intake manifold which is aluminum color, and fuel filter silver color un-coated steel. I found black yealds best temperature readings with hand held inferred temperature gun. Ambient temperature was 82*F.

Findings:
Top of fuel pump 140*
Top of head between manifold & valve cover front to back 239*-249*
Lower radiator hose at base 189*
Intake manifold @#1-122*, #3&4-229*, #6-235*
Carb front bowl 136*
Carb rear bowl 152*
Fuel filter 129* (two inches from carb)

The last two tanks of fuel were Sunoco's 91 octane "real gas" with no ethanol blended.

30 minutes later in shade, hood open since shut-down:
Top of fuel pump 122*
top of head as above: 180*
thermostat housing 176*
Lower radiator hose at base 108*
Intake as above: 162*, 159*, 155*
Carb front bowl 125*
Varb rear bowl 125*
Fuel filter 91*

I don't know if this helps, but it's some data someone can perhaps use somehow. Anyway it is a nice sunny day for a top down cruise.

Bill

_________________
67' Dart GT Convertible; the old Chrysler Corp.

82' LeBaron Convertible; the new Chrysler Corp

07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks for reporting about temperatures in your car. Do you have an older rebuildable pump or a disposable newer one?

I suspect that the problem might be with the fuel as I generally buy cheap 87 octane and they all contain 10% ethanol. I first drove my car in June after parking it since December with the last fill being on November 26.

While adjusting the carb's APT setting after the HEI upgrade in June, I learned that my P4070 electric pump definitely does not pass through any fuel while not running. I then replaced the electric pump with some 3/8" steel tube, which matched the rest of the fuel line.

On July 1 (28°C/82°F), I put in 20L of Shell 87 octane and managed to pull out onto the street where the car stalled. I thought that there might be an air lock in the line that the new mechanical pump wasn't able to pull through so I pushed the car to the Esso station next to the Shell station and put in another 20L of 87 octane to fill the tank and give the fuel pump a bit more head pressure. I put the hood up and it took about an hour for the tow truck to arrive and the car still did not start. Even later that day, the car would not start so I figured that my newly rebuilt mechanical pump had failed.

Before replacing the fuel pump with my other newly rebuilt spare the next day, I gave the starter another try and the car started and ran fine. A few days later, I ran some errands and the car ran flawlessly until my voltage regulator blew, at which point I had to drive home on battery power.

After replacing the voltage regulator, I ran some more errands a few days later on another hot day (29°C/84°F). After my first stop of 10 minutes after a 30 minute highway drive, my car once again stalled after pulling onto the street. I coasted to an empty driveway, put the hood up, and then walked to my next stop. It took me about 1/2 hour to return but my car would still not start so I poured 4L of water on the fuel pump, after which the car restarted and I was back on the road.

My 3rd stop was the rad shop (to discuss a transmission oil leak) - a 20 minute drive away on the highway. After getting off the highway and onto a city street, about 2 minutes after stopping for a left turn, my car stalled once again and I had to push it to the rad shop. 3 gallons of water on the fuel pump later, I was once again back on the road and made it home without any further problems.

I was not expecting my car to have stalled so many times with my new mechanical pump. I could switch to an ethanol-free 91 octane but I think that might be an expensive way to keep the mechanical pump, especially since I don't need the higher octane.

Your 140°F fuel pump temperature seems to be getting close to the boiling point for E10 gasoline. See YouTube video: Gasoline Boiling Temperature ((Way Below)) 220 Fahrenheit

The State of Michigan has some gasoline volatility data. From April to September, gasoline has the following evaporation temperatures:
10% evaporated - 158°F
50% evaporated - 150/170-250°F
90% evaporated - 374°F

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

In the past before installing new cam and bumping up compression I used 89 with 10% Jim Beam. Also no vapor lock problem then. With the new cam I wanted to continue using 87, but Maine seams to have changed its fuel laws allowing 90 or 91 alcohol free depending on provider to be dispensed in tandem 87 rotgut. Two grades now seam to be the norm around here. So while getting a handle on just what my newly rebuilt and configured engine would be happy guzzling I started with 91 until all the drivability bugs are worked out, and there has been an infestation during this brake-in.

You mentioned 3/8" fuel line, I thought slant six cars came with 5/16". Perhaps using a larger diameter tube has slowed flow velocity enough while still delivering needed volume exposing fuel to longer heat soak times. Also is pump putting out factory spec pressure which if less than required would lower fuel boiling point.

As for the age of my pump; can't explicitly recall replacing the one that was bolted up to engine in 2008 when I got the car (no notation in my records found). However, I did go on a fuel delivery up-grade crusade to be compatible with the then new 10% blends when they came on the market, and most likely replaced pump with one able to suck alcohol and keep on pumping; that would have been around 2009. Is a 9 year recollection long term or short term memory?... I hate working with old people. (sarcasm alert, refereeing to myself there)

_________________
67' Dart GT Convertible; the old Chrysler Corp.

82' LeBaron Convertible; the new Chrysler Corp

07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

When I installed the electric fuel pump back in 1988, the pump's nozzles were 3/8" and, since my original fuel lines were probably rusty back then (don't recall exactly now), I just replaced the entire run from the engine to the fuel pump with new 3/8" fuel line.

While the 3/8" line would slow the fuel's velocity, with no hot radiation sources nearby other than the road, I have my doubts that the fuel line would pick up much heat before the engine. The obvious heat source for heating the fuel is the pump as it's in contact with the block. I don't see the paper-thin pump gasket providing much insulation.

I was wondering if your pump looked more like the CARTER M60577 than the ones I had rebuilt (see Fuel Pump Repair Kits).

In a mechanical pump, the pump chamber alternates between pressure and vacuum with each stroke. If the fuel temperature in the chamber approaches the boiling point, the suction stroke could easily cause some of components of gasoline to flash into vapor. See Modern petrol in vintage engines - BP.

I'm not sure how much of a contribution a clean cooling jacket is to a hot engine block is but I've done a few citric acid flushes and the inside of my engine has very little rust or scale to impede heat transfer. See Cooling System.

_________________
1965 Plymouth Barracuda,
225 engine, Quadrajet, HEI, Dutra Duals, 904 Torqueflite, 2.76:1 axle, Addco front bar
Rods & Relics - Fort Erie, ON / Collector Car Tech

Yup, it's the Carter type; non rebuildable.

_________________
67' Dart GT Convertible; the old Chrysler Corp.

82' LeBaron Convertible; the new Chrysler Corp

07' 300 C AWD; Now by Fiat, the old new Chrysler LLC