[Randylk]

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.

[Schurkey]

Originally Posted by Randylk

won’t hardly start or run.

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?

[b-man]

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.

[Kenth]

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)?

[steve25]

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?

[dhcarguy]

Originally Posted by steve25

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?

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

[64speed]

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

[steve25]

He says his driving temps " stay great ".

[Formulajones]

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.

[steve25]

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.

[JLMounce]

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.

[Pershing]

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.

[kingbuzzo]

[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

[Randylk]

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?

[JLMounce]

Originally Posted by Randylk

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?

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.

[Randylk]

Originally Posted by JLMounce

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.

Pretty sure this is my exact problem. That was actually my next step. When I did the tune I wasn’t factoring in the heat soak. So I’m gonna put the 185 thermostat back in move my fuel lines and use a heat shield and spacer. I may adjust some on the fans on and off temp and see what happens. Thanks for the suggestions.

[Schurkey]

Originally Posted by Randylk

Has a $3500 radiator and fan set up from radiator entropy. New water pump

I don't know how a "radiator and fan set up" can cost $3500.

Originally Posted by Randylk

and a 165 thermostat.

Originally Posted by Randylk

Temp is 185-190 while running.

A 165 thermostat but it typically runs 20--25 degrees above the thermostat rating? The thermostat is not in control of engine temperature. The electric cooling fan MAY be in control--but perhaps not adjusted properly, or perhaps it's not in control either.

Originally Posted by Randylk

I may adjust some on the fans on and off temp and see what happens.

Your cooling system has genuine problems. PROBABLY related to the "$3500 radiator and fan set up". What temperature is the fan engaging? What temp does it disengage?

[bdk1976]

Originally Posted by Schurkey

I don't know how a "radiator and fan set up" can cost $3500.

My thoughts exactly. I have an iron head 455 that runs 180 all day with a stock water pump and a stock 4 row radiator. My entire drivetrain cost about a third of this guy's cooling system - AND runs way cooler. WTF?

[chiphead]

Originally Posted by Schurkey

I don't know how a "radiator and fan set up" can cost $3500.




A 165 thermostat but it typically runs 20--25 degrees above the thermostat rating? The thermostat is not in control of engine temperature. The electric cooling fan MAY be in control--but perhaps not adjusted properly, or perhaps it's not in control either.


Your cooling system has genuine problems. PROBABLY related to the "$3500 radiator and fan set up". What temperature is the fan engaging? What temp does it disengage?

Exactly this. If the actual engine temp is 180+ with a 165 thermostat, the cooling system has lost control of engine temperature. Either that, or the electric temp gauge has a wiring issue and is reporting incorrect temperatures. I'm struggling to see how a system gets 50+F temp rise on shutdown. There's a lot of latent heat or a radiator sizing issue. How much water does your system hold?

A cooling system with enough reserve capacity should be able to keep the engine at thermostat temp. I looked at "entropy radiator" and it looks like a very expensive billet version of the dual-fan setups we've all seen. I have NEVER had luck with a system like that. They don't flow enough air through the core, especially when the fans are off.

On my current '67, I just removed a dual paddle fan system like that and replaced with a stock clutch fan and shroud. Even with no thermostat it ran at the turn-on temp of the electric fans, 185-190. That's a sign of blocked airflow.

I ran the car with the clutch fan and no thermostat, and the hottest it got was 170 stopped in traffic and 150F going down the road. So with a good 180F thermostat, I know I have some reserve cooling capacity. It never gets over 185 when running, and when I shut it off, it climbs to 200 on a 96* summer day. Not bad for a used fan and shroud and a $50 fan clutch

The other thing to consider is sediment in the cooling system. If an engine has rusty or clogged cooling passages, the parts of the block sitting under sediment builds heat. Upon shutdown, that area sheds the built up heat to the water, which then spikes in temperature. If any rust or sediment is coming out during flushes, it needs to be flushed until the water runs clean. Also check the radiator for clogs due to crap coming from engine block.

https://entropyrad.com/collections/radiators

[Randylk]

My timing is perfect and so is the tune.