Fuel-Pump Hot Soak

[Mike76251]

Hello All,
I have a little teaser for you,
When I drive my truck and get it warmed up and then park it for a half a hour and crank it......it will sometimes run for 2 minutes or so and go dead. It is not hard to re-crank it after this happens.
This is hot-soak of the fuel pump happening.

Anyone out there had this problem?
What do you think......cool can?

I know this is trivial but nothing ever breaks or goes wrong with my truck and I like to work on it (!)
Mike

[sbc350gearhead]

Electric or mechanical?

[79BIG10]

I'm guessing it's electrical since all the heat soak I've ever heard goes with a electrical part of the engine.

Where do you have it mounted? Might look for a new location.

[Mike76251]

Nope Guys,
It is the block-mounted mech. one.
These are standard on 84s' like mine.
It also still has the third line on it (bypass)

[1FaastC10]

i've never heard of a heat soaked fuel pump before. starters, yes, but a fuel pump? i had my fuel supply line touching my header when i first installed them on my first 82. if that wouldnt cause a probem i dont know what would. what makes you so sure its a fuel problem? any diagnosing to back this up? i would investigate it IMMEDIATELY when it happens, as it is definitely intermittent.

[Mike76251]

What............no takers????

[Scrub]

Could the idle linkage be set too low, so when the choke is off the motor just doesn't get enough fuel to run?

I had one that did that, but it was a pretty old setup.

Good Luck

[Mike76251]

Scrub...thanks but that is not it.
I know it is heat soak because of the way it acts. It runs until all the fuel in the line from the pump to the carb gets used up and them stumbles.

[bigblock73]

Whatever it is, you do not need a cool can. Cool cans work but you have to keep ice in them...not only that, but typically only race cars or extreme HP vehicles need them.

I have NEVER heard of fuel pump heat soak either.

Have you checked your plugs? Are they fouled? Is the carb properly tuned?

...Jeff

[Mike76251]

Originally posted by bigblock73
Whatever it is, you do not need a cool can. Cool cans work but you have to keep ice in them...not only that, but typically only race cars or extreme HP vehicles need them.

I have NEVER heard of fuel pump heat soak either.

Have you checked your plugs? Are they fouled? Is the carb properly tuned?

...Jeff

Well......my truck certainly is no race car but I have had many problems with the fuel pump getting too hot.
California gas really gives it fits due to all the junk the State makes them put in the gas.
I know it is not fouled plugs (Bosch Platinums) or a tuning issue with the carb (Autometer Air/Fuel ratio gauge)

I promise....I promise.....I promise= it is heat soak of the fuel pump.
As I often tow 7,000lbs with my truck I know what heat soak of the pump feels like.
It could be a bad batch of gas come to think about it.
The more chemicals they put in the gas to lower emmisions/the easier it boils in the lines (lower vapor pressure).

[PHOENIX]

Now when you use the term heat soak are you talking about heat soak as in electric motors getting too hot and failing to operate correctly or are you talking about a raise in the engine coolant system temperature and pressure after the engine is turned off?

I never heard of a heat soak problem with mechanical fuel pumps, but I havent heard of a lot of stuff

Do you think the fuel lines are getting too hot or the pump itself is getting too hot?
If you think it is the lines, then wrap them with some thermal blanket type stuff. If you think it is the pump, then get rid of the mechanical pump and get an electric pump and install it in a cooler place. Gas itself is cold.
My solution to heat problems is....... electric fan.
Mount a little electric fan to blow on fuel pump (j/k)

When the truck is dying what does your a/f ratio gauge read?
My guess would be your problem is carb. or ignition.

Have you got up in the engine bay and watched the carb as it dies? Can you tell if it is running out of fuel when it dies?

How do you know its a heat soak pump problem for sure?
In other words what method did you use so others may use the same to test theirs if they have a similar problem?

[79BIG10]

Sounds like a bad fuel pump to me. It's not keeping up with enough pressure to substain the pressure needed.

[Scrub]

Hmmm....
How about "Vapor Lock". I haven't heard of it since the model-A Ford. It is when the fuel would get hot on the vacuum side of the fuel pump and rather than get sucked into the fuel pump as a liquid, it would vaporize and the motor would stop.

Do you have a hot muffler near your fuel lines? I have run engines pretty hard in some pretty hot places and never had a problem like you are describing. I'm thinking that something is just broken.

You mentioned that the fuel pump has a 3rd line. Could it be that heat is causing the bypass valve to bypass too much fuel and lowering your fuel pressure to the point that the motor starves out. So far, that sounds like the most likely culprit.

I don't know much about the fuel recycle system, but I would guess it has a pressure regulator of some kind, and that regulator could be affected by the heat.

Good luck.

[Mike76251]

Here is a little lesson about heat soak and mech. pumps=

The fuel pump pushrod is oiled on a small block by a drip system from the sump.This oil drip drains into the pump body and then out.
The hotter your oil is= the hotter your pump

When you put nearly any liquid under vacuum it's vapor pressure lowers (like gas on the vacuum side of your pump)

When you use "winter-time" gas in warm weather vapor lock problems increase (gas is different in winter ie; made to light off quicker to reduce emissions)

All these things can cause a "hot-soaked" fuel pump to vapor lock.


As for the symptoms of vapor lock........You are going along and the carb suddenly runs out of fuel. The engine goes dead. You let it sit for a while and it cranks right up because you gave the gas time to go back to liquid so the liquid pump (fuel pump) can pump it. If this happens while you are going down the road at a good clip then sometimes you can floor it and it will keep running. This lets more fuel through the lines to cool the system

There is nothing wrong with my truck as far as the carb, pump,
fuel lines touching anything hot.
My mufflers are 8" from my lines and those lines are covered with Kapton (what NASA insulates satellites with, ie:shiney gold foil)

This has happened with four different Delco fuel pumps.

I do not have a bypass valve in the system to fail.

My only solution appears to be a cool can.

My last trip through Texas during hot weather I had a cooler in the back and I would keep a rag in there with the ice....whenever I stopped the truck I would throw the rag over the fuel pump to cool it. This always works.

Thanks for the trys Guys,
Mike

[N2TRUX]

Mike, you are calling it "heat Soak" and that may be the correct term, but what you are describing is more commonly called "vapor lock". The more common cause of vapor lock is from heat at the carb, or lines going to them.

I had an 72 GTO that drove me crazy with a similiar problem. We replaced everything twice and it didn't solve the problem. I finally had an old school mechanic look at it, and he found the trouble.

For some reason the fuel return line was taking too much fuel away from the pump. He restricted the return line, and the problem went away.

This may not be the same, but it might be worth a look...

[Mike76251]

Thanks N2TRUX,
That may be a good suggestion.
The third line creates too much pressure drop in the system, this means the "vapor pressure" lowers and creates the problem.
This system was designed by Chevy engineers to prevent vapor lock............no surprise they were wrong!!