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.

Wouldn't a pontiac starter be somewhat useless under that kind of heat emanating from the block...at least until she cools down?

The sniper runs the fan in stall and crank?

I guess that would create a pretty easy test for the OP. When the engine is off and heat soaked, disable the fan in the ecu, then attempt to start.

If the solenoid is in good condition and the power lead from the battery is properly sized and in good condition, it's probably not a huge issue.

I still run a factory type starter, but it's fairly new. My engine soaks to about 210 if I've been hard on it and shut it down. No issues with cranking the engine after sitting for 5-10 minutes or so.

Spot on I believe
 

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.

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?

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?

Just curious…does it not turn over or turn over really slowly, or does it just not fire

I don't know, things are only getting more expensive. I just bought a radiator from Griffin for the Vega, that was $1200 alone, and it's not a very big radiator either.

I asked about that way back in Post #2, and never got a response beyond "doesn't have a problem cranking".

Can you post a picture of the radiator/fan setup?

Hopefully you are not using one of those dual electric fan setups with the shroud about 1" deep. They only use about half the radiator.

I'm wondering about this also like Schurkey. 165* thermostat and you say the engine runs at 185-190* It appears to me something is not doing a proper job in the coolant system. That's the other thing to that has been asked. What is the fan on/off temperatures. When the thermostat opens at 165* you better have the fans running. Do a test, turn your fans on when you start the engine and see if the thermostat controls your engine temp. Oh, put the new stat in first.

Like has been mentioned, change thermostat. Get a decent stainless thermostat from Napa. https://www.napacanada.com/en/p/THM1...QiLpSLPMSBSI4h

What kind of gauge are you running, or are you looking at the handheld for coolant temps?

Yup, pics would help a lot.

Water pump divider clearanced?

AC pulleys?

What BRAND T-stat? (And which one)

Are you running a bypass regulator or deadhead? (the Sniper internal regulators are known to be a problem)

Fuel heat soak usually isn't an issue at EFI fuel pressures so those changes aren't going to have any positive effect.

Look at the attached image, these are the relevant items, as well as the 'Cranking Timing' value.


.

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

I believe the term for spike in coolant temp after shutdown is 'after boil'.


.

None of the product shown on the home-page has a way to bypass air through the shroud when the fans are off, and the vehicle is moving fast enough to create a pressure differential between the front of the radiator and the rear.

Very amateur design work in my opinion.

Those shrouds should have a metal- or rubber flap that can open at speed to allow "ram air" movement, but closes when the vehicle is moving slowly or stopped.

I've been down that road experimenting with setups like that. It seems there are a bunch of radiator/fan companies that design there electric fan setups like that and every one I've tried always had an issue passing enough air to control engine temps. What ends up happening when I tried it is eventually the fans just run all the time, even on the highway, because even at speed it's a struggle to get air through the radiator when so much of it is blocked off. I had a big thread about it the last time dad wanted to try it on his GTO and even had Cold Case involved, adding holes and rubber flaps all around the electric fans where I could fit them and it was just never enough to control the issue.

I completely got away from those setups years ago and now only use a good quality radiator with the factory shroud and a clutch fan setup. Now I can't even get the engines hot in the AZ desert heat.

If a thermostat is rated to start opening at 180*, are we suggesting that the cooling maintain that temperature even when the valve is not fully open? I'll put my helmet on for this one as this makes no sense. It seems nornal to have the operating temperatures 15-20* above the thermostat rated opening point.

Some guys have probably over engineered their cooling system and can maintain coolant temperatures when the thermostat valve is only partially open and is what I think is actually going on here. And maybe to a lessor degree, guys with more modest cooling systems but with cooler air temperatures (less demand on system) see the same situation occuring. Seems to be a bit of stretch to say a cooling system has "lost control" not maintaining the thermostat rated starting opening temperature but never overheats the engine. My cars run 180* thermostats and typically run 195-200* no matter what I throw at them, driving style wise, and see almost zero ROI chasing something like this down.

Who cares? It looks cool and costs a lot of money. Must work!

Yeah, this is what I was always led to believe. A thermostat's purpose is to maintain cooling system pressure, and to set the minimum operating temperature. The cooling system's capability and efficiency is ultimately what determines the temperature the car runs at. If your cooling system is bulky and well-designed enough to actually open and close a 160 thermostat in closed loop operation, then great, If not, it'll operate at a higher temp and eventually stop at what the cooling system can support. The only issue with using a thermostat at too low of a temp that your cooling system can't maintain, is that said thermostat will always be open and you lose some of the system's ability to make pressure.

Here is my experience with 160* thermostat in both vehicles. The 160* thermostat starts to open at 160* and it only takes a less than say 15 sec to be fully open. Having said that the cooling system in both cars maintains the 160 degrees give or take a few degrees. If the coolant system is design/ working properly there is no 15/20* swing in temperature. As the coolant temperature increases or decreases that is when the thermostat modulates to accommodate the coolant system.



I can run my car with the 160 * thermostat in any outside temperture and it never goes above 160*.


The Firebird with the IA2 at 789 hp is a different animal, only runs at the track.On the street in really hot, 85-90* F weather it cannot get enough air through the radiator when driving slow with the electric water pump and dual fans. At the track if only hits around 170-175* in same hot temperature outside. So it has a 160* thermostat and the system cannot keep up when the vehicle is driven slowly in very hot weather. At the track with heat it up to 160* and do the 1/4 mile run with it reaching 170-175* when back at our pit.



Morel of all this, if you have a 160,165,180,190 degree Stat the coolant system should maintain that temperature.

A thermostat's purpose is to maintain cooling system pressure, The thermostat does not maintain system pressure. The Radiator cap is doing that job.

This make no sense to me.

^^^ Lemme reword that. It helps act as a RESTRICTION, which helps aid in maintaining pressure.

And I really don't understand what's hard to interpret about what I said. I'm basically validating the point you made in your post prior to your replies to mine. A cooling system that is efficient and has enough capacity to actually maintain the thermostat's temperature setting will maintain it in closed loop operation (the modulating thing you're talking about). If it's not up to snuff, then the engine temp will be higher than the thermostat rating, meaning the thermostat will always be open as it tries to lower the temperature, but it cannot. This is like not having a thermostat. At that point, whatever temp the car runs at is what the cooling system is capable of maintaining on its own. Every engine is going to run at its own unique, inherent temperature. Compression ratio; power output; water jacket and passage design; ignition timing; valve timing; and fuel mixture all play a role in the temperature an engine will inherently run given. If you have a very good, or at the very least, SUFFICIENT cooling system, then yes, the thermostat will be able to regulate the temperature at or near the thermostat temperature by opening and closing in closed loop operation. However, if your cooling system doesn't have the capacity to allow the thermostat to keep control, your temps will run away and either overheat, or stop at a higher temperature than the thermostat that the engine inherently "likes."

I may have come off sounding somewhat Condescending there. for that I'm Sorry.

Chuckie, and your second reply is closer to the truth. There are TWO sources of pressure in the cooling system:
1. Static pressure set by the rad cap, and
2. Dynamic pressure created by the water pump moving fluid against "a" restriction. The other side of the main restriction (generally the thermostat, but it could be the radiator) is going to be the suction side of the water pump, with reduced dynamic pressure. What makes this more complex is that there's a hundred tiny restrictions in the cooling system, including but not limited to the small holes in the head gasket, the heater core, the narrow passages of the water jacket as it goes around the cylinder bores, and so forth.

#2 is why designers moved away from vertical-flow radiators to cross-flow radiators starting in the '60s. A vertical-flow radiator has the pressure cap on the upper, HOT tank, the entry to the radiator core. If the radiator core gets restricted--scaled-up--the radiator becomes more of a restriction that the water pump is pushing against. This overloads the rad cap especially at high rpm, releasing water into the overflow tank at best, or to the pavement at worst. Either way, there's now less coolant in the system and greater chance of overheating.

A cross-flow radiator has the pressure cap on the COOL tank, on the other side of the core. It is effectively on the suction side of the water pump, so the suction side runs at rad-cap pressure and everywhere else has higher pressure due to water pump motion. The cross-flow radiator is generally better at "everything".

The thermostat SHOULD be the "main" restriction in a cooling system, even when the thermostat is fully-open. Whether it is, or not, depends somewhat on the condition of the radiator, and sometimes, whether the correct head gasket has been installed.


The real problem is that if the thermostat is already fully-open at idle or cruise, there's no reserve cooling capacity for when the engine is run harder. The only cooling system efficiencies at that point are faster water pump speed, faster fan speed, and--maybe--faster vehicle speed leading to some "ram air" effect at the radiator.

Automobile radiators are always undersized compared to the horsepower the engine is capable of. Compare a 400 HP automotive radiator to a big-truck (semi, or bus, or bigass farm truck) with a similar HP rating--the automotive radiator will be tiny. This is because a 400 HP auto engine is rarely run at 400 hp, and when it is, it's generally for short bursts. The big truck 400 hp engine may run at or near full throttle for hours on end. Automobile radiators are sized to easily handle idle and cruise with a little additional capacity, truck and bus radiators are sized to handle WFO throttle.

Take a 427 Chevy. The car engines were rated up to 435 hp, they had the usual thermostat and radiator-hose. The 427 tall-deck truck engines had maybe half that horsepower, they had governor-carburetors to limit RPM, and they had TWO thermostats of the same size and capacity as the single thermostat in the car engine, and a monster water pump. Look at the "cock and balls" thermostat housing on one of them--two rounded thermostat areas, plus the GIANT snout for the huge-diameter upper radiator hose. (Photos shamelessly stolen from the Internet. https://www.tradecraftspecialties.com/bbckb#Topic4
https://www.tradecraftspecialties.co...es/Intake1.JPG

https://www.tradecraftspecialties.co...atHousing1.JPG


An automobile or light truck with a 180 thermostat should idle and cruise within a few degrees of 180. Let's say 185-ish. Thermostat open, but not very much. Then when the throttle is opened further--to go up a hill, or to beat the guy in the next lane--horsepower goes up, heat goes up, and the thermostat can open farther to allow the cooling system to reject more heat into the airstream going through the radiator.

That's exactly what happens when something is wrong with the cooling system, or something is wrong with the engine tune so the engine creates more heat than it should. There may be an undersized radiator, a faulty radiator, not enough ignition timing, faulty fan/fan clutch, incorrect pulley ratio between crank and water pump, or any one--or combination--of additional faults too numerous to mention.

Nope. That's the way it's supposed to work; assuming a water-pump driven cooling fan.

You toss an electric fan into the mix, and now the coolant temperature is dependent on both the coolant thermostat rating, AND the cooling-fan thermostat.

My '92 and '93 Luminas with electric fans don't have the fan come on until 210 degrees. I think the second fan comes on at 220.

The thermostat is fully open at about 20 degrees above it's rating. I suppose this might vary a little depending on thermostat design. But fully-open at +20 degrees from it's rating is a fairly safe bet. Anything beyond +20 degrees, and the thermostat is no longer in control of the temperature.

You have a 180 thermostat, so at 200 degrees, that thermostat is almost certainly fully-open and no longer controls the engine temperature. You have NO way to increase coolant flow through the radiator except to add RPM (fan and water pump speed) and/or vehicle speed. Your cooling system needs improvement, or your engine needs tuning/friction reduction. (Often a matter of more spark advance, (vacuum advance) richer cruise air/fuel mix, lower-tension/thinner piston rings to reduce friction, verify piston-to-bore clearance for friction reduction, lower exhaust restriction/block exhaust crossover in intake manifold, and so forth.)


Very close. I've added some corrections to your statement.