Forum Discussion

TOMMY47's avatar
TOMMY47
Explorer
Aug 21, 2013

VAPOR LOCK

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.
  • Since you found the filter below the driver did you replace it?

    Take it off and try to blow through it. Those filters were supposed to last 100K miles per the manual but mine was blocked with 11K miles. The big issue was not mileage but years. Most folks don't put many miles on an rv and they can get plugged just like carbs due to fuel varnishing.

    I chased the same problem for a couple of years before the in tank fuel pump finally really started acting up and I had to replace it. Found that fuel filter plugged so bad I couldn't blow through it.

    Hot days, hard pulls, both would cause vapor lock symptoms.
  • ReelTime wrote:
    Tommy,
    There was no overflow radiator tank on my unit and the water level in the radiator was (with the radiator cap removed, engine cold) around 2 inches from the top when full. The radiator itself was the expansion tank for that year model.

    The "expansion tank" subject appears to have various opinions and different set ups on various vehicles.
    Any cooling system benifits from haveing an expansion tank more accuratly called a coolant recovery system. It's possible that aftermarket body prep/rv vendors fail to reinstall the tank when thier work is complete. In any event you should make certain one is used even on older vehicles and stationary engines. If yours doesn't have a tank or has a tank where coolant level doesn't rise when hot and fall when cool,check the radiator cap. The cap must have a gasket rather than metal to metal where it contacts the filler neck. For best preformance,the tank should mount near level with radiator cap and of course be connected by leak proof hose. The tank automaticly purges air (same as manual proceedure explained above by Simplygib) on every heat cool cycle. Just add water if tank is less than 25% full when cool.
    The benifit is less pump cavitation,no air bubbles insulating between liquid coolant and metal of engine and radiator which henders heat transfer.
    I don't think this is the issue with Tommy's rig but is simply a link in the chain of cooling events that some might not be aware of.
    However,I believe the overheating should be addressed first. The lose of power may very well clear up becaues we know a hot engine doesn't perform well.
  • j-d wrote:
    Does that filter look like one of the ones in this pic? Proabably the uppoer one?




    ...snip...T-Bird, with early TBI, did not have a Mass Air Flow Sensor. It did have an Air Charge Temp Sensor in one branch of the Intake Manifold. It's a Thermistor, and a Cold Engine caused a High Resistance, which increased the Pulse Time to the Injectors, like Choking a Cold Engine. This was happening on the road, and the car would slow down, sometimes stop, in a cloud of black smoke. So rich it couldn't keep running. Not saying this is happening to you now, but it's a condition I ran into that sapped the engine's power.


    Tbird didn't have MAF, but did have a MAP sensor with its speed density system. The ACT alone is not enough to throw serious fueling issues like what you are talking about. ACT is a "modifier" for existing fuel/spark tables and can only sway things a little each way...

    Irregardless, I do agree with your comments about the fuel filter and it's ability to flow air when blowing through it. It was probably gummed up pretty heavily...
  • Well, I don't have the expertise to start dismantling things 1500 miles from home, so I am not pulling filters now. I did wrap the fuel lines with a metal reflective tape that is supposed to prevent 90% of the heat from reaching the lines. Tomorrow, I'll find out.
  • Good news, so far. Drove up I25 from Colorado Springs through Denver to Loveland.
    Had a few long hills where I was in 2nd gear with the engine whining away and the temp gauge creeping up--No issues at all. Later at a traffic light in Loveland the temp spiked real high--again, no issues.
    So far, it looks like the reflective tape shielding is doing its job.
  • Thanks for the update TOMMY47. Great ifo. for others having the same issue.

About Technical Issues

Having RV issues? Connect with others who have been in your shoes.24,190 PostsLatest Activity: Jan 19, 2025