vapor lock 440 dodge engine

[fireball440]

I need some ideas on this. Here is what I have and what I have done to correct well.. not correct but minimize the problem that I still have.

I have a 1977 Apollo That suffers from vapor lock. The first time it was encountered, we had gone over the sierras and down into Reno. Past Reno heading out on highway 50 the engine started to lose power. By the time we got to Austin, Nevada about 120 miles from Reno, the vehicle almost came to a stop. I let it sit for about 4 hours until dark. Once night came it started right up and worked great. Going over the Salt Lake it started doing it again;. We just drove at night and in the early hours the rest of the trip

Once I got it home I did the following items:  Placed heat shield between electric fuel pump and exhaust pipe, Installed a ram air system to suck in cooler air from the front of the vehicle instead of behind the radiator. Wrapped all the fuel lines with aluminum foil. Replaced the Clutch Fan Did a full tune up to include timing, cap,rotor and plugs with wires. Rebuilt carburetor

Coming back from Yellowstone thru Twin Falls, Idaho, it started doing it again. Slowed to about 40 mph lifted off the dog house cover and top of the air cleaner within about 10 Min's the engine was running fine.   

The wife is giving me a lot of pressure to get this thing fixed, She does not want to have to be the co pilot repair person. The question I have is there anything else I can do to cure this. Is there any type of fuel additive I could use?  The engine does not run hot it just loves to vapor lock.....

[RV Mech Tech]

fireball  440  - a few ideas here:
1)  Where is the fuel line routed at the front of the engine? is it out in front  of the water pump/timing chain  cover or is it routed behind the pump between the pump and block/t.c. cover?  - this is a common source for a fuel line to get too hot and vapour lock to occur - as I have mentioned in another post the engine compartments on some of these earlier RV's had little to no air flow around the engine and in some cases this lack of air will contribute to these kind of problems - you have already ducted cooler air from the front because of this - if the line is routed behind the pump rerouting it in front would help a lot in allowing any air to have a cooling affect on the fuel.
2)  You also mentioned that you installed an heat shield between the exhaust pipe and fuel pump - maybe this is where the fuel is gathering a lot of heat- I would move the fuel pump to another location in the line if possible- if the pump is located close to the engine compartment, try and move it back towads the middle of the chassis- when you are driving a lot of the heat from the compartment will be forced back over the area immediately behind the engine and down and over the powertrain and exhaust system area - that's why an engine oil leaks gets distributed towards the back and covers everything.
3)  There used to be a carb heat shield available from the speed shops (MR. Gasket) and this mounted between the intake manifold and carb (you could make one yourself out of thin aluminum)  and kept a  lot of the engine heat away from the carb- this is one location  where the hot fuel can turn into vapour -inside the fuel bowl - I have seen several carb casings warped because of excess heat as well as fried gaskets, cracked intake and exhaust  manifolds etc.- would it be possible to install an electric fan(s) at the front to force more air over the engine? maybe not the full sized engine cooling fans but smaller 12 volts fan(s) that could bring fresh air over the rad shroud and over the engine -  if you have the room you could install these fan(s) off to the side and duct the forced air over the engine - I have seen this on emergency vehicles where they have a ton of added on equipment such as a second alternator or auxiliary hydraulic pump that adds a lot of heat - also is there anything that can be moved from around the engine compartment off to the side? - most of these earlier RV's had little to no spare room but if you could do this it would allow more air movement - G.M. had a service bulletin on the P30 chassis in heavy duty application that had these same problems - the first bulletin suggested ducting cooler air from the front over the exhaust manifold to prevent them from cracking and the second concerned vapour lock- it was  a kit that included an electric fuel pump to be mounted near the gas tank to assist the mechanical fuel pump at the engine in case of vapour lock - (a band-aid solution)
4)  Another idea is to have a small cooler in-line in the fuel line somewhere similar to a power steering oil cooler (also seen on emergency vehicles/RV's) - this would have to have fittings and not just rubber hoses and clamps and this would bring the temp down considerably- let us know how the fuel system is set up.    Hm?

[duramax]

HI:

It has been 15 years since we had a 440 with this problem. I fought vapor lock for 3 years but finally cured this. I cannot say which mod did the job as I did multiple changes at the same time. Part of the problem is forcing all the air into the engine compartment. I built a stainless scoop under the front of the rad. I used a Chev PU scoop as the model. I changed all the fuel lines to 1/2 inch steel and rerouted any that were in hot areas. I found that insulation made the problem worse. I used a large Carter engine pump and mounted the electric pump at the rear. Most electric pumps are pushers. The idea is to pressurize the fuel line as this raises the boiling temp of the fuel. I installed a clutch fan from a 454 chev as the dodge unit does not function as well. I also had an auxiliary electric fan. You must use the correct thermostat. I also found that I could reduce the exhaust heat with headers and a 3 inch exhaust system and school bus mufflers. Finally I was able to drive in 95 degree weather without problems. BTW: To quickly cure your vapor lock just pour some water on the lines or fuel pump. Hope this helps.

[DaveVA78Chieftain]

Do you still have the Thermoquad installed or have you replaced it with an Edlebrock carburator?
Remove the carburator and look underneath it to see if there is an excessive carbon build up underneath that would transfer heat to the carburator bowl.  75 and later Dodge rigs use an EGR system.  As such, the engine runs leaner and hotter.  That also means the intake manifild can run hotter.

Dave

[fireball440]

Thanks for all the input here is what my set up is. The fuel pump is located about 5 feet behind the engine on the passengers side of the frame. I used a duel thickness cookie sheet as a heat shield. it was the best place to tie into the fuel line for the electric fuel pump. I think I am stuck with that location. I will try and add some more insulation if possible. The fuel line is located from the pump up the side of of the frame and then to the side of the engine. It then runs up and over the engine to the carb. I wrapped foil from the carb all the way down to the side rail on the fuel line. The line is metal from the carb to about 2 feet from the engine then it goes to rubber and then metal once on the side frame rail back to the pump

My carb is a stock rebuilt Thermoquad with a ceramic base. This keeps the carb up off the manifold.  I have almost no room to move anything around for more air flow  I have entertained some radical ideas that the wife is not happy with..

run fuel line thru the refrigerator to cool the fuel down.

leave the dog house off when driving to enjoy the heat and supersonic noise.

apply wet towels to the fuel line and have the wife apply water as we drive...

dont drive in the heat.

I will investigate adding a scoup under the radiator to bring  in some kind of cooler air. The vapor lock seems to be at its worst when it is about 95 degrees and I am running at about 65mph or so. It also takes about 4 hours of driving to have it start acting up.

[jkilbert]

I talked to a friend of mine , who is the service manager at one of our local Dodge dealerships. He agreed with everything that everyone has posted. he added one though and that is about today's gasoline. He said that the formulation of the gasoline used today is designed for fuel-injected engines not carburated. it has a lower vapor pressure which means that it boils at a lower temp.  in a fuel injected engine there is a return line that constantly returns fuel to the tank, thus giving you relatively cool fuel. on our carburated engines it just sits i the fuel bowl and will boil very readily, thus the vapor lock. And by the way our old '79 Dodge B-300 ambulances did the same thing.  to add extra airflow on our ambulances we used the nice chrome bilge vents like you see on most boats to allow more hot air out from under the hood

[ClydesdaleKevin]

We had a bad vapor lock problem on our old RV, the Ark, with a 413 engine.  Turned out that the previous owner installed NON vented gas caps!  These things need vented gas caps so you don't get a vacuum in the gas tank.  The way I realized what the problem really was when I removed the caps and there was a whooshing sound as air surged into the vacummized gas tank.  I switched to vented caps, and the problem was solved.

Kev

[RV Mech Tech]

fireball440 - the best on is " leave the dog house off when driving to enjoy the heat and supersonic noise!!"     - your idea of running the fuel line through the fridge is actually done on race/drag cars - the fuel line is run up to an aluminum canister and coiled inside it and the racers put dry ice in it before a run to keep the fuel cool -  if you wanted to do this you could get one (or make one) through the auto high-performance aftermarket (Mr. gasket for example) - if  the ambient temps are going to be very high then you could use this method  when needed  - I have seen two owners with older RV's do this for the same reason - the service manager in jkilberts post about fuel quality brings up a very valid point and the older engines are designed to run on the fuel that was available when those vehicles were built - older engines had mechanical controls and were subject to ambient air temperature  and moisture changes  and  computer controls and fuel injection eliminated all of that so they  can produce fuel with a lower vapour pressure  so that what comes out the tailpipe is cleaner  - the things you have to watch out for is detonation and pre-ignition  ( knocking/pinging ) when using today's fuels  since the earlier RV's did not have knock sensors and did not retard the ignition timing when problems occurred - and with the recent stricter emission laws brought in by the current administration in the USA and Canada as well  they are going to try and eliminate the additives they put in premium fuel that make the older engines run better (MMT for example)  - they started planning this back in the 60's and the goal is to eliminate any additives altogether by making vehicles that do not require this premium fuel or additives  to operate and we will see the day when anyone who has an older vehicle will have to pay a hefty price for fuel  that is not considered "GREEN Fuel" .