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Hot fuel pump!

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sparkydave

sparkydave

Jedi Knight
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I think I might be getting to the bottom of my random vapor locking. I don't think it's an air leak anymore. Friday it was hitting close to 90 degrees, and on the way home, it stalled 3 times. The last time I finally took the cover off the pump, and the fuel was boiling inside the pump! I think I found the problem! It's bad enough I would get it running, it would run for about 1 mile, then stall again. At least the last time it made it to the hilltop so I was able to coast all the way back into my garage under gravity power.

So, given the engine doesn't appear to be overheating (temp gauge reads about 190 when it's running), is this just normal to have the fuel pump get blazing hot? At this point I'm ready to plunk down the $80 for the electric pump from Moss and just bypass the mechanical one completely, but is there any other reason the pump could be getting so hot, other than it's bolted to the hot engine? Could the engine be too hot even though the temperature gauge is reading normal? Bear in mind it's a new temperature gauge and I checked it in a pan of boiling water, so I know it reads right.
 
The only thing I can think of that would make a mechanical pump run hot is that the actuating arm is not getting lubricated :eeek: ! A Facet electric pump bought at a local parts house would be considerably cheaper than either a Moss or VB unit!! :wink:
 
I think I would make sure the fuel line is not against the exhaust or some such dumb thing. I know I know it could never happen.
 
a couple of years ago, I burned out the fuel pump on my Passat (when we live in Orlando) The VW guy asked if I filled up the tank from completely empty. I said of course. He said, better to fill it up when 1/2 or 1/3 full as the gas doesn't heat up as much. Apparantly the heat of the gas from the sun affected the pump somehow. I didn't follow it up as it was a warranty job, but, gas can boil at as low as 100 deg depending on variables

JP
 
JP, in the FI VWs, the fuel pump is located inside the fuel tank! It probably heated up because it was running "in the dry" rather than the heat of the sun affecting it!! 1/2 or 1/3 of a tank would keep the pump submerged and therefore cooler, I would think!!
 
I would think that just the fuel passing thru it would cool it more than enough to keep it from boiling!
If it's a soliniod type fuel pump the coil may be shorted.
if thats the case I'd make sure your extingusher is charged!
Is the pump fused? Is it the correct size?
One more thing, your scaring the heck out of me!
 
The only thing that surprises me about Spridget fuel systems is that some people actually don't have vapor-lock problems. Modern fuels do boil at ordinary under-hood temperatures. At one point I replaced my fuel lines with vinyl tubing, just to see what was happening in the lines. Looked like ginger ale, and bubbles formed everywhere they could.

How hot is the fuel pump getting? It's clamped to the block, the block gets hot, so the pump will get hot too. So, a hot fuel pump, to some degree, is expected. The movement of fuel through the lines will provide some cooling, but not a whole lot--I once calculated that it's moving only about 2 1/2 inches per second at 60 MPH. That gives it plenty of time to heat up as it goes through the part of the line in the engine compartment.

I also found that the fuel didn't move well through the aftermarket fuel filters that everyone uses.

My solution was a Facet pump, mounted near the tank, and rerouting the lines so they are continuously upward. That way, the bubbles rise and blow through the float bowl vents. Also, I have only one filter, at the input of the pump, none at the carb inlet. No problems with vapor lock since doing this.
 
It sounds like you have no heat shield? Is the pump exposed to radiant heat from the exhaust manifold? Consider a heat shield to keep the manifold from heating up the pump. My engine is totally custom and I've run into heat/vaporlock issues twice. Each time, it was because I'd made some change that exposed some part of the underbonnet fuel system to the radiant heat of the manifold or turbocharger. Air flow under a spridget bonnet is pathetic and heatshielding can be very helpful.

Glen
 
Well, I checked on the fuel line routing, and found it's nowhere near the exhaust. Thanks for the tip, Jack. So where does one find one of these Facet fuel pumps for cheap? I did a search and found them on JC Whitney, but they look just like the ones Moss sells and cost about the same. The only other one I found was a Bosch pump that Advance Auto sells for about $55.

texas_bugeye: The stock 1500s have a mechanical pump bolted to the engine, not an electric pump. Since it has to suck fuel up from the tank, putting the fuel under suction while it's going through the already hot pump makes it boil at a lower temperature, which I expect is part of what's happening. Putting an electric pump down low to push the fuel up to the engine as Steve says puts the fuel line under pressure instead of suction (and helps force liquid fuel even if it boils further down the line), so hopefully that will eliminate the problem. I was just surprised that seems to be a more recent problem, but perhaps Steve is correct in saying modern fuel is more volatile, hence vapor locking is a bigger problem now.
 
My solution was similar to Sarastro's. I also re-routed the fuel line to run down the passengers side (away from the exhaust side), and across the front of the engine (down low)where hopefully airflow will help keep the fuel cooler!
 
Glen_B said:
It sounds like you have no heat shield? Is the pump exposed to radiant heat from the exhaust manifold? Consider a heat shield to keep the manifold from heating up the pump. My engine is totally custom and I've run into heat/vaporlock issues twice. Each time, it was because I'd made some change that exposed some part of the underbonnet fuel system to the radiant heat of the manifold or turbocharger. Air flow under a spridget bonnet is pathetic and heatshielding can be very helpful.

Glen
Click to expand...

The fuel pump is on the other side of the engine from the exhaust; it's nowhere near it. It is however bolted to the block with only a thin gasket between it and the block. Even so, I expect the cam lever carries heat nicely from the camshaft to the pump too.
 
OOPS! You have a 1500! I was referring to a 1275! :blush:
 
A thin gasket! Aha, a wrinkle... are you sure you have the correct pump / pump arm, and that you shouldn't be running the 1/2" fuel pump spacer?
 
I'm running with the same fuel pump the car came with, which has the straight lever, not the curved lever. The curved one takes the thick spacer. I had to replace it once (misdiagnosis of a different problem), but the aftermarket pump developed an air leak in the screen cover, so I put the old one back in.
 
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