Heat Soak Theory Question

AndyG

Because some other guys are perverts
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I have a friend who thinks heat soak is really a result of the age of the vehicle resulting in a weakened fuel injection check valve, and this allows the fuel to escape creating the issue-

Has anyone replaced a fuel pump in recent times and noticed a change for the better?

Just curious if his theory may have merit.
 
Too absolute of a rule...unless the postulated theory is specific to 4.0s or straight sizes with intake/exhaust on the same side.

I've replaced my injectors with OEM Siemens rebuilds. Didn't have an issue with heat soak before...had a possible issue after during a 1600 mile road trip during 100 plus degree weather down the WABDR. No overheating during the trip.

Got home and installed a DEI heat shield on the fuel rail.

Also replaced a failing thermostat...Jeep wasn't reaching operating temperature.

I've had my fuel pump in and out a couple of times. New pump and two regulators. I think my current one needs replaced...only doing 33-35 psi...that or my gauge is off.

What specifically is your issue?

-Mac
 
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I have a friend who thinks heat soak is really a result of the age of the vehicle resulting in a weakened fuel injection check valve, and this allows the fuel to escape creating the issue-

Has anyone replaced a fuel pump in recent times and noticed a change for the better?

Just curious if his theory may have merit.
If the check valve was leaking the pressure in the system would result in a lower boiling point. When the fuel boils in the line or the rail the injectors won’t pass the vapor very well to the combustion chamber. The engine will run rough until the pressure increases and cool fuel fills the injector rail. Here is the technical explanation.
As the pressure applied to the liquid surface is increased, the energy needed for the liquid molecules to expand to gas phase also increases. Hence, a higher temperature is required to change liquid to gas phase. So, boiling point of liquid rises on increasing pressure.
 
If the check valve was leaking the pressure in the system would result in a lower boiling point. When the fuel boils in the line or the rail the injectors won’t pass the vapor very well to the combustion chamber. The engine will run rough until the pressure increases and cool fuel fills the injector rail. Here is the technical explanation.
As the pressure applied to the liquid surface is increased, the energy needed for the liquid molecules to expand to gas phase also increases. Hence, a higher temperature is required to change liquid to gas phase. So, boiling point of liquid rises on increasing pressure.

Yes, we know that happens- do new fuel pumps prevent the problem , hence proving the weak check valve theory has merit-
 
Too absolute of a rule...unless the postulated theory is specific to 4.0s or straight sizes with intake/exhaust on the same side.

I've replaced my injectors with OEM Siemens rebuilds. Didn't have an issue with heat soak before...had a possible issue after during a 1600 mile road trip during 100 plus degree weather down the WABDR. No overheating during the trip.

Got home and installed a DEI heat shield on the fuel rail.

Also replaced a failing thermostat...Jeep wasn't reaching operating temperature.

I've had my fuel pump in and out a couple of times. New pump and two regulators. I think my current one needs replaced...only doing 33-35 psi...that or my gauge is off.

What specifically is your issue?

-Mac

I’ve had heat soak in several- could weak check valves contribute.
 
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I replaced my fuel pump a few summers ago and my heat soak issues were either the same as before, or worse.
 
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Yes, we know that happens- do new fuel pumps prevent the problem , hence proving the weak check valve theory has merit-

The check valve hold pressure if you had one that reduced the pressure it would be possible but usually from my experience a failed check valve will drop all the pressure out of the fuel line causing long crank. I would look into heat transfer to the fuel line. I know I had heat soak a few time and my hood vent solved that issue.
The check valve theory absolutely has merit but in practicality from my experience I would look at heat shield and insulation of the fuel lines.
 
These things are prone to high engine bay heat and poor airflow under the hood. The non-crossover head doesn't help either. The DEI kit is good as it keeps the direct heat off the rail and injectors. I think the hood vent helps some as well especially after shutdown and while parked to let the heat out of the top of the hood. Ultimately these engines should have had a return style fuel system installed from the factory, but I'm sure cost overruled function. I did a return style on my TJ and it makes a difference.
 
I can see where one could draw that conclusion as on the old carbureted engines you could often cure vapor lock with a new fuel pump, or by adding an electric in-line fuel pump.
Now as far as a new fuel pump curing it on our Jeeps, I can't say but I will say that I have no extra heat shielding on my 2000 and I had a weak fuel pump and or regulator when I bought it, but I had zero heat soak issues with the fuel system, so when I replaced the pump and regulator naturally I had no change other than it now starts immediately without cycling the pump. I don't really understand why I didn't have issues as I live in a very hot climate and it seems I would be the perfect candidate for it.
I did have heat soak issues with the cooling system to where just a few minutes of idling would start to boil in the overflow, and shutting down without a cool down period would result in the bottle boiling and over-flowing. I have since cured that with a new Mopar radiator, and by switching the AC compressor off when I am within a minute or two of my destination, no more boiling under the hood.
 
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These things are prone to high engine bay heat and poor airflow under the hood. The non-crossover head doesn't help either. The DEI kit is good as it keeps the direct heat off the rail and injectors. I think the hood vent helps some as well especially after shutdown and while parked to let the heat out of the top of the hood. Ultimately these engines should have had a return style fuel system installed from the factory, but I'm sure cost overruled function. I did a return style on my TJ and it makes a difference.

Returnless fuel systems are installed for cost and emissions. Returning the fuel to the tank causes a lot of vapors in the tank that need to be dealt with through the evap system.
 
Here's another factoid: Mid summer last year, I replaced my fan clutch with the "heavy duty" Hayden that everybody seems to complain about its noise. I *NEVER* had a heat soak incident afterwards. Yes, this is anecdotal and I'll have a better idea in about 10 months from now, but it seems to indicate the additional air flow is doing something. Lower underhood air temp before shutdown? *shrug* It also is giving me cooler engine temps, but that's anecdotal as well - the old clutch was apparently bad, so there's that. *another shrug*

I have the insulation kit on Cyl #3.
 
I have a friend who thinks heat soak is really a result of the age of the vehicle resulting in a weakened fuel injection check valve, and this allows the fuel to escape creating the issue-

Has anyone replaced a fuel pump in recent times and noticed a change for the better?

Just curious if his theory may have merit.

Tell your friend to use the scientific method if he wants it to be more than "what if". Someone could easily install a fuel pressure gauge and record data during hot starts.

Need to check the check valve? Same pressure gauge is used to find bleed off and replace if out of spec.

They could also key on several times before starting to prime the rail before hot starting and record instances of hot start miss.
 
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Tell your friend to use the scientific method if he wants it to be more than "what if". Someone could easily install a fuel pressure gauge and record data during hot starts.

Need to check the check valve? Same pressure gauge is used to find bleed off and replace if out of spec.

They could also key on several times before starting to prime the rail before hot starting and record instances of hot start miss.

He doesn’t need schooled, he only offered his opinion what could be contributing.
 
Here's another factoid: Mid summer last year, I replaced my fan clutch with the "heavy duty" Hayden that everybody seems to complain about its noise. I *NEVER* had a heat soak incident afterwards. Yes, this is anecdotal and I'll have a better idea in about 10 months from now, but it seems to indicate the additional air flow is doing something. Lower underhood air temp before shutdown? *shrug* It also is giving me cooler engine temps, but that's anecdotal as well - the old clutch was apparently bad, so there's that. *another shrug*

I have the insulation kit on Cyl #3.

Thanks Zorba-

Good post.
 
Here's another factoid: Mid summer last year, I replaced my fan clutch with the "heavy duty" Hayden that everybody seems to complain about its noise. I *NEVER* had a heat soak incident afterwards. Yes, this is anecdotal and I'll have a better idea in about 10 months from now, but it seems to indicate the additional air flow is doing something. Lower underhood air temp before shutdown? *shrug* It also is giving me cooler engine temps, but that's anecdotal as well - the old clutch was apparently bad, so there's that. *another shrug*

I have the insulation kit on Cyl #3.

Here was Fords fix.
 
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