Overheating headache

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alg

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I have a 71 demon with a 318 engine and three speed transmission. During a restoration the engine was rebuilt. Modifications to the engine included a performance cam, Holley 4bbl carburetor, electronic ignition, and headers. I had some initial issues with engine overheating especially when idling.
I replaced the radiator and put on a factory original fan shroud.
Monday I took the car for its first short outing in about 18 months. The engine ran at about 180 degrees when moving, but after about a thirty minute ride, while backing up my driveway and into the garage (about a five minute exercise) the engine temp quickly increased to past the 220 degree reading, and upon shutting down the engine the temp quickly rose to way past the 240 degree reading.
Antifreeze poured out of the overflow, but only after the engine was shut down.
This engine has less 200 miles on it.
Is it common for temp readings to go so high after shutting down the engine? I have no experience in this but know this cannot be good.
I am going through the cooling system now in an attempt to determine and correct the possible cause(s). I would like to blame the headers, but just don’t know.

Thanks guys.
 
Had a similar issue with a fresh 383. Stock but added a clutch fan. It ran too hot, and overheated regularly.
Eventually found out it was running too lean and needed a timing adjustment.
Amazing how much cooler since.
 
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It IS normal for engine temp to rise after shut off, nothing is moving the coolant or cooling it. This is why a lot of newer cars have electric fans, and after coolers, etc. However, your engine definitely has an issue, whether tune related (for sure) or mechanical. What overheating issue did you have early on, at idle? Was that corrected?
 
Things to check are the radiator cap, do you have a big enough fan to pull the needed a i r during times where no air is flowing through, like idle?
What initial timing does it have?
6 or 8 impeller water pump?
8 moves more coolant at low speeds*
 
Newer engine will run hotter

So many things to consider!

You say new radiator. Does this include pump, shroud, hoses and a High Flow T-stat, and the correct PSI cap for the radiator?

What is the base timing and the total timing curve?

All of this really maters and simply checking off the boxes sometimes hides minor things that get major.

Backing up the driveway should really not make it heat up. Heat soak and temp rise a little is normal.
 
It’s amazing how many times this has been covered already. Please use the search feature. Loads of useful info there already.
What you’ve done is nothing new. Good luck!
 
royslead said:
It IS normal for engine temp to rise after shut off, nothing is moving the coolant or cooling it. This is why a lot of newer cars have electric fans, and after coolers, etc. However, your engine definitely has an issue, whether tune related (for sure) or mechanical. What overheating issue did you have early on, at idle? Was that corrected?
Click to expand...
It overheated the same but lower temps. I replaced the radiator and added an NOS fan shroud. That was four years ago. I’ve hardly run the car since. These numbers are at least 20 degrees higher. I am going to measure the fan tomorrow, but it is a more stout fan than the original.
When you say tune related that refers to timing? I haven’t checked that. Could headers cause excess temps more than stock exhaust manifolds? I bought this car new, and the timing was always TDC. Will have to address this too. Could headers cause excess temps more than stock exhaust manifolds and dual exhaust?
I have some work to do.
Thanks for your reply.
 
Syleng1 said:
It’s amazing how many times this has been covered already. Please use the search feature. Loads of useful info there already.
What you’ve done is nothing new. Good luck!
Click to expand...
Thank you. I’ve done that and been reading for five days.
 
Headers are not your issue.

Basic Stuff is as always! Pics are sometimes worth a thousand words and 20 questions!

Let's start there!
 
Does it run at a constant 180 or does it get cooler and then goes back to 180 ?
 
Forget the headers being a source of the problem. You are already on the wrong track. They are not the issue. When you accept that fact you can then get on the right track to diagnosing things by focusing on cooling components. The coolant is possibly not circulating properly. That’s where I would start. Thermostat, flow blockage. Start with the basics as laid out in a factory service manual. You got one of those??
 
alg said:
It overheated the same but lower temps. I replaced the radiator and added an NOS fan shroud. That was four years ago. I’ve hardly run the car since. These numbers are at least 20 degrees higher. I am going to measure the fan tomorrow, but it is a more stout fan than the original.
When you say tune related that refers to timing? I haven’t checked that. Could headers cause excess temps more than stock exhaust manifolds? I bought this car new, and the timing was always TDC. Will have to address this too. Could headers cause excess temps more than stock exhaust manifolds and dual exhaust?
I have some work to do.
Thanks for your reply.
Click to expand...

The headers themselves will not be the problem; but if they were hammered nearly shut, to make them fit, they would hold back exhaust flow and could, mind you "could" but probably not increase engine temp in various spots. This is a reach, and you would likely have other drivability related concerns as well. So, let's assume the headers are out of the equation. Is it possible the thermostat got put in backwards? Is the fan on a clutch or direct bolted to the water pump pulley? I've seen bad fan clutches cause lots of overheating issues. Did you say the engine was rebuilt? By whom? I don't want to knock anyone's work without seeing it firsthand, but could be warped heads, deck surfaces, bad head gaskets, everything else that has been mentioned, etc. By tuning, yes, I was referring to ignition timing / fuel mixtures. Let's start by watching the coolant with the radiator cap off. Do you see any flow, after it is warmed up or does it erupt / boil over right away? What does it smell like? What color is it?
 
You are in Fl. Probably never gets that cold.
Pure water is an excellent conductor of heat. AF is not. When you add AF to water, you reduce the water's ability to transfer heat. You should use only enough AF to suit your climate, & if a hot climate none at all.
 
While there can be a great debate over use /types of COOLANT / antifreeze, you should never use straight water, unless you plan on flushing often. coolant added to water increases the boiling point, helps lube the system, and helps prevent rust and corrosion.
 
alg said:
I replaced the radiator and put on a factory original fan shroud.
Click to expand...

This statement tells the board nothing! What'd you replace the radiator with? A older, more plugged up one or Brand new??
alg said:
Monday I took the car for its first short outing in about 18 months.
Click to expand...

So almost 2 years now since you replaced it, how nasty was the radiator when installed, 2 years later will only make it worse if it was properly prepped to begin with!
alg said:
I am going through the cooling system now in an attempt to determine and correct the possible cause(s).
Click to expand...

You should've done that 2 years ago before you put it all back together! But what do I know?
 
12many said:
When you accept that fact you can then get on the right track to diagnosing things by focusing on cooling components.
Click to expand...

Amen!

This post will be lost shortly due to the Fact the "OP" is in denial as to what the real issues are!
 
My post #14. Yes, what I said about limiting AF for your climate will ensure best cooling & transfer of heat from the coolant to the rad core.
Pure water boils at 212*. With a 16 lb rad cap, the b/point is raised to 260*. If you need a BP higher than 260, then you have other problems.....
Some people confuse AF with rust inhibitor, two different things.
 
overheating issue resolved. I found a machinist locally who made me a very nice 5” water pump pulley which has increased my fan speed to the factory recommended 1.3:1 water pump pulley to cam shaft pulley ratio. Also added hood to radiator coil seal, replaced the water pump, and added a radiator overflow reservoir. Temp now stays 180-190 all the time.
Thanks to all who chimed in on this thread.
To 1969383s who wrote #18, your avatar is my reply.
 
alg said:
overheating issue resolved. I found a machinist locally who made me a very nice 5” water pump pulley which has increased my fan speed to the factory recommended 1.3:1 water pump pulley to cam shaft pulley ratio. Also added hood to radiator coil seal, replaced the water pump, and added a radiator overflow reservoir. Temp now stays 180-190 all the time.
Thanks to all who chimed in on this thread.
To 1969383s who wrote #18, your avatar is my reply.
Click to expand...

Glad to hear you got it sorted out.
 
IMO, the pulley was NOT your problem .
A ratio of 1.3 is extremely high.
I'm glad it solved your problem, but now you may have a new one(s)
which being how to keep the belt on at rpm. So you are gonna have to keep your eyes on the gauges after/during every hi-rpm blast.
At 30% overdrive, 5500 crank rpm is now 7150 water-pump rpm. Good luck keeping the belt on.
If you have a 5-blade (or more) all-steel fan, then, my guess is that;
1) the idle-timing is retarded,
2) AND/OR the ring-gaps are too tight,
3) AND/OR the skirt clearance is too tight.

If the low-speed timing is late:
the mixture will not finish burning in the chamber, and so;
the first six inches or so, of the headers, will run very hot, sometimes even glowing red.
The exhaust ports will also run hot, transferring heat directly into the nearby water-jackets.
The exhaust valves will run hot, pushing their heat into the heads.
your exhaust system is a wildcard. Obviously, a restrictive system will back the heat up all the way to the exhaust valves. If you pressure test it, I shoot for less than 3.5psi .
Fuel consumption will be atrocious.
power and torque will be down.
Your street engine might like the following timings, just guessing;
Factory ignition timing means nothing.
you MUST have a working Vacuum Advance system.
idle-timing of about 12 degrees, with a manual trans.
PowerTiming not more than 32/36 depending on many factors
Stall timing of 20 to 28*
Cruise-timing in top gear of ~56* at 2600rpm
Cruise-timing in second gear at 30/35 mph of ~44*
============
Just for reference;
The pump on my 367HO manual-trans car is underdriven , and runs an ancient rad from a 1973 Dart, plus a thermostatic clutched fan. It will idle down to 550 in gear and pulling itself along in parades at 3.5 to 4 mph....... endlessly. At idle, the pipes run about 400* +/-50.. I run Dual 3inch pipes all the way to the bumper.
 
I have to agree with AJ here. I believe what you've done with the pulley, although it helped, is acting like a band aid for the real problem, whatever that might be. You're in Florida in the winter. What's this going to be like in the dead of summer in stop and go bumper to bumper traffic? At 190, in the winter, I just bet will equate to 210 in the summer, all else being equal. That's not giving yourself much cushion.
 
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