VAPOR LOCK

[TOMMY47]

I'm experiencing what I believe is vapor lock in my 1990 E350 Class C.
Happens when I climbing hills, especially when it's hot out. I can see the engine temp gauge rise and start looking for a wide part of the shoulder of the road. 10 minutes of cooling down and I'm on my way again.
In looking on line for cures for VL, I have not seen any that involve changing the thermostat out for one in the 180 degree range. Not sure, but I probably have one in the 190-195 range. The engine is always running right in the middle of the temp gauge until I start up a hill.
Wouldn't having a lower thermostat result in lower heat transfer to the gas line/forward fuel pump, thus preventing VL??
Any other suggestions would also be appreciated.

[TOMMY47]

Reel time--You described exactly what is happening.
The black canister was further back in the line when I noticed it was leaking gas a lot under stress. I crawled under and could feel that it was not seated correctly. Took it to a shop in Wyoming and they unscrewed it--no filter inside, threading damaged and O ring flat as a pancake. The were unable to get a replacement canister and placed a filter directly on the line. The setup I now have is 2 filters directly on the line. I'm going to take a look underneath and see what everything looks like near the engine plus look at the radiator for blockage. If the lines are real close to the engine, I'll probably heat shield them.

[Simplygib]

Another piece of info that may or may not apply to your particular vehicle. Cooling systems with the overflow tank are designed to run with zero air in the system. Some vehicles are very sensitive to this and will overheat if air is present. Some have bleeder valves to bleed the air out, but in any case air can usually be removed by turning on the heater temp to full, removing the radiator cap (on a cold engine), topping off with coolant and then running the engine at a fast idle with the radiator cap removed until engine reaches normal operating temperature. During the process keep a watch on the coolant level and keep adding more as the air bubbles out. At some point usually within ten minutes or so the bubbles will cease and you will only see coolant swirling around. Top off again and replace cap, then make sure coolant level in the overflow tank is within range and the overflow tube is connected and in good condition.

[j-d]

I looked up 1990 E350 chassis and proceed on the (always risky) assumption it's 460-V8-EFI. If so, it uses two, maybe even three, electric fuel pumps. One Low Pressure Pump PER TANK, then a High Pressure External pump. The only external high pressure one I ever dealt with was frame-mounted on a T-Bird. Ford shortly after eliminated the frame-mounted and moved the high pressure pumps to the fuel tank(s). I think that by the year they went EFI on the 460 in E350 (which was 1989 Chassis Year, very possibly what's under your 1990 coach), most of tham had one large gas tank instead of the two-tank setup common in the early and mid-1980s.
It sounds like you replaced the frame-mounted high pressure pump, and most likely the associated filter. Change the filter if you have not, and see if there's a Pressure Test Point where you can measure pressure at the Throttle Body (or Fuel Rail). Takes a Fuel Pressure Gauge, I think 40PSI or a little higher. But you may have a failing Low Pressure, In Tank pump. If you change it, you must change its strainer too.

Overheating... Do you have a factory Fan and Thermostatic Clutch setup? And are you gearing down? On a steep hill, you should be in Second Gear, around 45MPH, engine winding up, and the Fan Screaming. Needs to be Factory Fan with a good Factory type Thermostatic Clutch. Aftermarket "viscous" clutches and "Flex Fan" conversions won't hack it. Radiator needs to be clean in and out, Thermostat opening wide. And exhaust can't be crimped or plugged.

[TOMMY47]

This is fuel injected, 460 engine. It has 2 fuel pumps--one in tank, 2nd near the engine. Happens with any amount of fuel. I've only had the RV since November and am on the tail end of a 3 1/2 month trip.
I can check the fan and radiator visually now but am limited in other options until I get back.

[ReelTime]

Tommy47, I can relate to your issues and maybe contribute some information that may help.
I owned a 1990 Rockwood class C on an E350 Ford chassis with a 460 7.5 ltr engine.

The chassis was manufactured in 1989, the first year Ford put Fuel injection on that motor. In cold weather it ran fine but in the summer It would loose power on hills to the point of stalling the engine. If I let it set for 20 minutes it would start right up and run and pull normally until the next hill.

After talking with some local knowledgeable mechanics they told me that Vapor Lock on a fuel injected motor was rare but not impossible. First suggestion was new fuel pump. That helped but did not completely solve the issue.

Next (if you have the same motor) look on the drivers side below the drivers door, mounted to the frame rail you will find a black canister. It looks like a smaller oil filter. Ford calls it a "Fuel Delivery System" They put it on some Early Ford 460's. it simply UN-screws like a oil filter but it has a fuel filter inside (The first of two). Go to an auto parts store and get another filter, it will be in a box with a new "O" ring gasket. Open the box and throw the filter away and use the new gasket (make sure the old one is removed) and reassemble the canister without the filter. Just ahead of this is the second fuel filter just inside the frame rail, replace this one with a new one.

This solved my problem and here is my opinion on the issue. The motor was simply running out of gas when hot. I believe and one of the Ford technicians would not Deni that the Fuel Delivery System was just a small reserve of fuel when engine demand was greatest. All pumps do work better when they are cool.

Now on the Over Heat issue, I would leave the standard 190 degree Thermostat alone. The gauges on a 1990 model are not the "smart" gauges we now have. The gauges on vehicles of that era would respond to variations with a wide range. On my 1990 460 the standard after warm-up was mid-way. Going up a hill or in a pull 3/4 way was normal. Around town and stop and go Mid-Way on the gauge was normal. Down the interstate in summer at 60 mph 3/4 way all the time. I get to town it is back mid way. If you notice the Oil pressure gauge( after warm up) shows a wide range depending on idyl vs take off.

If you have the same motor I hope this helps, it is from experience and the 460 is a proven motor despite what the engineers were forced to do to it because of the EPA and emissions testing.

[93Cobra2771]

Changing the tstat to a lower temp one won't help your problem. You need to do some investigating to determine a few things.

1. Do you have a check engine light on?
2. Have you verified your fuel pressure under the conditions you mention above when it starts getting hot? Fuel pressure is VERY important.
3. How much fuel is in your fuel tank when you experience the issue (fuel pump is cooled by the fuel in the tank. If the tank is low on fuel, the fuel in the tank starts getting heated up by the return type fuel system).


It would be helpful to know which engine you have.

Irregardless, you need to address your overheating issue, as opposed to trying to fix the problems resulting from it. Could be old/clogged radiator, could be the cooling fan clutch, missing fan shroud, lots of things to look at before assuming vapor lock. In a properly operating car, vapor lock will not happen unless some fuel line rerouting has occurred or you are getting WAY hot.

[YC_1]

Sure sounds like in tank fuel pump but you state you changed that. Is there a fuel filter along the frame rail below the driver?? If so, have you changed it?

[Dave_H_M]

I think you need to cure that heat problem. Has it always been that way?

[DO_N_DAT]

If your mh has an electric fuel pump in the tank, vapor lock is not your problem.

[da_bees]

Every engine is desighned to operate at a certain tempature,most commonly 190F. The rise in temp you are seeing is the result of restricted radiator,worn water pump impeller,poor or non-operation of coolant fan and/or any number of things. If you are not into this type thing,better get somone who is before engine is damaged. Vapor loc is somthing I hadn't heard for many years but since you mentioned it,I don't think that is the problem. The F series trucks have the fuel pump at the tank and I expect your E is also. Starting with simple things,ckeck for bugs or grass on or between radiator and ac condenser. Look inside at passages in radiator if possible. There should be no accumilation what so ever. If fan is electric,it should be running full speed when temp rises and continue long after pulling to roadside. Raise the hood and look next time this happens. If fan is belt driven,after engine warms to operating temp,kill engine and attempt to spin fan by hand. If the fan freewheels when you give it a spin,the clutch is defective. Is there a shroud in place around fan? That's only a start but maybe it will help.

[TOMMY47]

Already got a new fuel pump and it has helped a little. However, I do plan to insulate the pump and line if I can reach them easily. A company called Thermotec seems to have various insulating products and I've seen them at an auto parts store.

[time2roll]

Get a new fuel pump and insulate the fuel line.

[elkhorn98]

My dad had the same problem on a 1989 bronco. One time a tow truck driver stopped to help us and said it happened all time and you just have to bleed the air out of the fuel line at the valve stem looking thing. After finding that out we could be back on the road in <1 minute.