Heat soak
 

Hey guys I’m having an engine heat soak issue. I just put a lot of money in my car and I’m having a heat soak issue often I drive it. I put the best stuff in the car and the temp stays great while driving but when I shut it of the temp will rise to 250-260 and won’t hardly start or run. I do have the complete Holley sniper kit with hyperspark. Runs amazing it’s only after I turn it off and try to restart often a few minutes. And suggestions on a fix for this? Btw it’s a 455.

Describe what actually happens.

There is a giant diagnostic difference between "won't crank", "cranks slowly", and "cranks but won't run".

Does it:
Not crank?
Cranks slowly?
Cranks at normal speed, won't start?
Starts, runs poorly?
Something else?

Share details about your car. Like exactly what car?

Radiator, fan setup, engine mods, anything you can list will help others to help you.

At this point we know it’s a 455 and we know your fuel and ignition setup but nothing else.

What can you expect from toys with names like "sniper" and "hyper"?
You won't find them in the troubleshooting guide in Pontiac's Service Manual, that's for sure.

Anyway, may be as simple as a weak starting battery, corroded wires, bad wire connections/wires, missing ground cables, low quality battery switch (f.e. the green knob breaker)?

Your coolant temp should not rise to that extent when you shut the car off.

Are you running a 50/50 mix of antifreeze and Demineralized water?

If it’s getting that hot sitting then something is very wrong! What are your driving temps?

He says his driving temps " stay great ".

For an engine to rise to 250-260 degrees after shut off I would have to guess driving temps are already pretty damn hot.

At normal temps, where I run my engines anyway, I only see them rise to maybe 190 or so after shut down.

Also at a true 250 temp if your idiot light is still hooked up and the sender is good then after the car has been sitting long enough for the temps to rise then if you just turn the key to the position before the engine cranks then that light should be on.

I would do what Steve said after a good flushing of your system. Also , do you have a heat shield on your starter?

You didn't state what the car runs at when it's in operations. Assuming you're running iron heads, there's still a good bit of heat soaked mass that coolant will soak. But to the extent of going to 250-260 degrees is excessive. Unless of course the engine is running at 230-240 degrees to begin with. The delta here is what matters.

Do you run headers or manifolds? Again this is an area that there is going to be a lot of heat and it may point to your issue. If the tune is off, you may have very high EGT's. If you're got uncoated headers or iron manifolds with very high EGT's that would also pump heat back into the system that the water would soak after shut down.

I had the same problem. Car ran great but after shut off I would get coolant coming out of the overflow tube. The Coolant gauge spiked at max. That was a bad thermostat. A new thermostat solved the problem.

On a different car after an engine rebuild: it ran great but a bit on the hot side but still within the gauge normal range but toward the Hot side of the gauge. If I tried to start it right after the hot shut off, the starter was strained. It would barely turn the engine. But after maybe 5-10 seconds or so, it would catch and the engine would start. (cold starts were perfect.) The culprit was the timing was way off.

These are two easy things to check. good luck.

Driving temp is 185
 

It’s a punched out 455 with iron heads and stock manifolds and big cam. Didn’t build the engine and don’t know a lot about it. Was in the car when I got it. I flushed it 3 times yes 50/50 mix. Has a $3500 radiator and fan set up from radiator entropy. New water pump and a 165 thermostat. To low maybe? I’m thinking the ecm in the sniper is getting too hot and giving me issues. Or maybe the fuel lines because I have them running along the intake. Doesn’t have a problem cranking. It’s like I’m getting fuel and ecm issues. Maybe some sort of heat shield under the sniper and move the fuel lines?

Timing
 

My timing is perfect and so is the tune.

Running temp
 

Temp is 185-190 while running.

[QUOTE=Pershing;6526215]I had the same problem. Car ran great but after shut off I would get coolant coming out of the overflow tube. The Coolant gauge spiked at max. That was a bad thermostat. A new thermostat solved the problem.

same for me...bad thermo was the culprit...thought she was going to c h e r n o b y l when I got to the car meet

Try a 180 T stat. My 470 had a 160, Would open at 160, but would run hotter on street, and a bit more heat soak. 220-230 on shutdown. Changed T stat and now 190 driving, 205 tops heat soak. Ya T stat was opening, but not properly due to age is my guess

You can try an insulating spacer under the sniper to help with that.

It sounds like this is a crank and no start issue after a short heat soak.

What may be happening is that as the car sits for a bit and soaks some heat, the fuel film that clings to the intake manifold runner and for which the ECU in the throttle body calculates some fuel usage, may be evaporating.

As a result, when you go to hit the key, the car cranks over but the throttle body is not providing enough fuel initially to both re-wet the intake manifold and start the engine. Typically you'd get a symptom of endless cranking, or the engine may fire, stumble and die.

If that's what is happening, you need to look at your hot cranking fuel in the tune. You may need to make some adjustments there. To figure out if you need to add or remove cranking fuel, complete the following test.

When hot and heat soaked, attempt to start the engine. If adding a small amount of throttle helps the engine start, you have too much cranking fuel and need to reduce it.

If adding throttle does not help the engine start, you are lean and need to add hot cranking fuel.

Fuel boils off at 150 when it’s not under enough pressure to keep it from boiling.

When a EFI system is off there’s no pressure.

Without question move and insulate your fuel line and put in a new T stat since there much cheaper then rebuilding a seized motor.

If I understand your symptoms right, the starter turns the engine over fine, but it won't crank up when hot. My bet is that you have a low voltage issue going to the Sniper system. In the condition you are describing, if the radiator fans are variable and on the high setting, they along with the starter draw, this could be dropping the voltage too low for the Sniper to run. I have run into this exact same scenario before where the engine fires fine when cold but has an issue starting when hot and the fans are on, especially if you're getting the Sniper voltage through the ignition switch or off the fuse box.