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Discussion Starter · #21 ·
There are MANY opinions, rituals, and practices when it comes to anything cars. Cooling is no exception. In my experience, a clean and well designed system always works well. And in my experience, when that isn't true, then something else is wrong.

I've heard that water pump impellers make a big difference with Pontiac. Are you using a good, name brand pump, or a parts chain rebuild?

As for the thermostat, bypass holes shouldnt make or break your system... However, as I mentioned, when all else is right, they can add to efficient operation. It's not likely that they will cure your issue.
Thank you! Pump is ACDelco.
 

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Discussion Starter · #22 ·
Good advice all around, work the temp gun. Shrouds matter, and electric fans need shrouds too. Spiking at idle is directly related to air flow from fans, inadequate if it gets too hot...

a good temperature activated clutch fan properly shrouded may help. But like PJ said your timing matters especially at idle. Too retarded causes hotter exhaust and thereby heats up everything...a thermostat partially stuck can give you many issues too, if you open the system replace it. Even a new one can be bad.
Thank you!
 

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Discussion Starter · #23 ·
A lot of info, bit still not enough.

Did you rebuild the engine back to the stock 335HP rating, or go bigger?

Still use the "670" heads and stock compression?

Stock points distributor?


Gotta know EXACTLY what your initial timing is, what your total timing is, at what RPM total timing is achieved, and how much additional timing do you get from the vacuum advance can.

Let's start there and we can then move to the next round of questions. (y)
Thank you for the response!
Rebuild is stock 335.
Heads are 670 and stock compression.
Distributor is Pertronix electronic
Gotta check on the timing. I'll get back with you.

Thanks again!
 

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Discussion Starter · #24 ·
There are so many different things that can cause high temps.. Bear mentioned on problem that is often over looked..
Another issue is sometimes the one of the sleeves (or both) gets left out between the water pump and timing chain cover.
View attachment 142219
Is your fan shroud installed?
Checking your temp at the thermostat housing with a laser thermometer will help trouble shoot. (as well as other places on the engine and radiator)
You mentioned electric fans.. My experience with those has been horrible at best..
A good mechanical fan with a good fan clutch and fan shroud should be all you need..
Another possibility is a faulty water temp sending unit..
there are lots of places to check.
Can you upload a pic of your engine compartment around the radiator/front of the engine?
Hello! The current configuration is OEM with shroud installed and fan about half way under shroud. Electronic fans didn't help even with shroud. I'll take a pic and come back. Thank you.
 

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Discussion Starter · #25 ·
Not all electric fans are created equal as well. Do the fans have a shroud or are they just zip tied to the radiator? Whats the fans size and how many CFM do they pull?

Also Whats your idle and cruise timing set at?
Electric fans with shroud were pulled. Back to OEM setup. I'll be checking on the timing. Thanks!
 

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Discussion Starter · #26 ·
are you running ac pulleys ??? big crank small water pump
or is the water pump and crank pulleys the same size basically ?
they are different diameter than non ac ,,,, and provide more water pump rpm
Hello and thank you. Pulleys are AC...one big, one smaller
 

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I beleave 1x8 that was the technique he was using to flatten the plate to get the clearance required. When you check the radiator temp is there any hot or coldspots on the radiator? When you filled the radiator. Did you see good flow after the thermostat open?
 

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The plates have been checked and rechecked but I don't know the distance from the impeller off hand. Would you help me out with the 2 pieces of 1" x 8"? I don't follow that. Thank you!
The way I did mine was to remove the pump, secure it in a vise (carefully), and lay the plate onto the pump with no gasket between the plate and the pump. "Work" the plate with a suitable hammer until it's just barely touching the pump impeller all the way around. When you reinstall with the gasket in place, clearance will be perfect.

Bear
 

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1. I have a Holley Frostbite 3 row, rated by Holley as capable of handling 700 hp. My engine is standard 400/335.
2. High flow thermostat. I've read various opinions about pro/con and am uncertain. I'm not refuting you but my logic is that hi flow has coolant more quickly pass through the radiator giving it less time to cool. Where am I wrong?
3. I had not thought of an engine oil cooler and like that idea very much. Looking into it!
Thank you. Much appreciated!
Not sure where the speed of the coolant BS originally surfaced on the internet. There are those who don't use a thermostat and simply use a restrictor disk, or even a large washer without issue. I hope this post puts all the "too fast" coolant flow BS to rest.

From the Stant thermostat website:
"Thermostat Failures
A thermostat fails to “open” if the return spring breaks or debris prevents the thermostat valve from fully seating or closing; allowing a steady flow of coolant to the radiator, overcooling the engine - This results in poor warm up and heater performance, increased engine emissions and reduced fuel economy"

From Hot Rod Magazine:

"If the coolant temperature never increases up to normal operating temperature, it is likely your thermostat is stuck in the open position. If you know your thermostat is opening but your cooling system still is running a warmer than it should, a solution might be to switch to a high-flow thermostat."

And Finally, from the H.A.M.B. website, posted by Ebbsspeed:

"Myths

For those that cling tenaciously to myths, I am going to take one last crack at forever dispelling the Granddaddy of them all when it comes to cooling systems.

The myth is stated as either:


  1. Coolant can be pumped too fast through the engine for it to absorb enough heat, or
  2. Coolant can be pumped too fast through the radiator for it to cool properly, or
  3. Cooling can be improved by slowing the flow of coolant through the radiator so it cools more completely.
NONE of these is true. The simple truth is that higher coolant flow will ALWAYS result in higher heat transfer and improved cooling system performance.

The reason the myth is so persistent, is that: a) without knowledge of fluid dynamics and laws of thermal conduction it does make a kind of intuitive sense and b) it is based on a tiny kernel of truth, but that kernel of truth does not explain the overall system behaviour and so, interpreted out of context, leads to a completely erroneous conclusion.

So, let's start with the tiny nugget of truth. If you had a sealed rad (no flow) full of hot coolant, and subjected that rad to airflow, yes, the longer you left the coolant in the rad, the more it would cool. However, if you were to plot that cooling over time, you would find that the RATE at which the cooling takes place is an exponential curve that decreases with the temperature difference between the hot coolant and the air. Put another way - when the temperature difference (delta-T) between the hot coolant and the airflow is large, heat transfer (cooling) initially takes place very, very quickly (almost instantaneously). But as that happens, and the coolant cools, the delta-T becomes less, and the RATE at which further cooling happens gets less and less until the point where the coolant and air are almost the same temperature and continued cooling takes a very long time. This is Newton's law of cooling. To illustrate this, recall my "quenching steel in a bucket" analogy.

A good example of this law can be seen when quenching a red-hot piece of steel in a bucket of water. At first, the temperature difference (delta-T) between the red-hot steel and the water is huge - therefore the initial heat transfer occurs at a great rate - the steel initially cools very fast - almost instantaneously. However, after this initial cooling, the delta-T is much smaller, so the remaining cooling occurs much more slowly. If you removed the steel after a second or two - it has cooled a lot - but it will still be warm. To continue cooling the steel to the temp. of the water, you have to leave it in there quite a bit longer - because as it cools - the rate of cooling continually decreases as well. In short - initial cooling is fast, but subsequent cooling occurs more and more slowly until cooling that last little bit takes a long time.

So what does this mean? Basically it means, the longer the coolant stays in the rad, the less efficient the cooling that takes place is - to the point that the rate of cooling is so slow as to be detrimental to overall system cooling. Better to dump the big load of heat right away and go back quickly for another load than hang about waiting for a last little bit of insignificant cooling to happen."

From Water Pump Manufacturer Flow Kooler:

Doesn't coolant need more time in the radiator to cool?


No.
But a lot of people still think so. We have come up with some explanations for the Doubting Thomas.

Debunking the I Can Have It Both Ways Theory

The water has to have "time to cool" argument is most common one we hear. In a closed loop system if you keep the fluid in the heat exchanger you are simultaneously keeping it in the block longer. Unfortunately, the block is the part that is generating the heat. Sending hot coolant from your source (engine) through the heat exchanger (radiator) to the sink (air) will transfer heat as long as there is a temperature difference between the source and sink. The engine is still generating heat the whole time so why keep the coolant there any longer than you have to.

Debunking The Conscientious Electron Theory

We hear that the coolant has to stay in the system longer to cool but what is heat transfer really but conduction, convection and radiation of electrons. The fluid in your system transfers those electrons based principally on the source-sink differential and the exchange material's transfer rate. An electron moves at varying speeds - Bohr's model has it moving at 2 million meter/second and with a mere 11 million eV boost you can get an electron to 99.9% of the speed of light. Though they move at varying speeds physicists accept that electrons move fast - really really fast. Far faster than the flow rate of the water pump. Your engine coolant's electrons do not know (or care) how fast you send them through the system - they just knows that the source is hotter than the sink and off they go.

Debunking Grandpa's Flathead Theory

"But wait a minute, I know Grandpa used to put washers in his flathead to slow the flow and cool his engine." We know people did this too. They still do it but the cooling benefit is not from the slower flow but the increase in dynamic pressure in the block that builds from the restriction. Consider that Grandpa had two flathead water pumps sending twice the volume through the same size radiator core as the Model B 4 cylinder. Too much flow in this no pressure system results in fluid loss. Slowing flow rate helps prevent that. At some point Grandpa maxed out the throughput and began building pressure in his block. Increasing block pressure helps reduce the onset of hot spots on his cylinder walls and formation of steam pockets in his block. This is a real benefit and does help cooling but is only realized when throughput nears capacity or is at capacity. While these restrictions may make sense when your rpm is excessive or your flow rate exceeds your heat exchanger throughput, they do not make sense for most applications. If you doubt this thinking then try this simple Ask Dr. Science experiment; clamp off the lower hose while you watch your temp gauge. Hopefully, you will debunk Grandpa's theory yourself before you experience vapor lock and melt your engine.

Flow restriction is not all bad if it serves to prevent cavitation. Cavitation occurs when a pump turns so fast that you generate lower pressure and air bubbles or vapor forms. These bubbles eventually implode and damage the engine block wall and impeller. Rapidly spinning the impeller can literally rip the air from water but may not actually move the fluid, it's tantamount to turning an eggbeater in a paint bucket. Restricting the fluid flow to raise system pressure in the block may help prevent cavitation at higher RPM but is it necessary for most vehicles? Probably not.

Most vehicles do not need to restrict flow because they do not reach or sustain high RPM. Additionally, thin aluminum radiators already restrict by design e.g. fewer rows of thinner tubes. Restrict it further and you may as well hose clamp the lower radiator hose and we know how that works out. When you face Grandpa on the track you may want your washers, otherwise, keep them in the toolkit.

Simply put, you have a far better chance of keeping your cool with greater flow rate through your heat exchanger and exiting the system than holding it in your heat exchanger while generating heat in your engine block.
2. Low Flow Luddites or..."the guy at the shop said"
When we are chasing an overheating problem, its common to seek help and who better than the guy sitting at the counter in a parts house or the countless experts begging to be heard on internet forums. They are generally excellent credentialed sources but we sometimes meet a low flow believer who thinks heat exchange is determined by how long the fluid stays in the block and how long it stays in the radiator. We fall back on simple logic. FlowKooler pumps achieve higher flow rates through a better impeller design. The high flow rates are seen far earlier on the rpm curve than OEM and self-professed "performance" pumps which use OEM-like impellers. The flow is more efficient builds block pressure sooner which helps in preventing cavitation. All good stuff which no one would refute. The low flow proponent' s argument of "too fast" begins to falls down when we discuss flow itself. If spun fast enough, even the most poorly designed stamped steel impellers will achieve the same hi flow flow rates. Granted they may cavitate, they may pump less efficiently and it will always occur at higher rpms. The point here is whether a discount design pump was spun at hi rpms or our well designed pump was spun under normal driving conditions; flow is flow. Can it be logically argued that a hi flow pump flowed coolant too fast if an OEM pump achieves the same flow rates. No, it cannot."
 

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Lemans guy,"Spiking at idle is directly related to air flow from fans, inadequate if it gets too hot... "

PJ: Not necessarily. Could be timing issues - vacuum advance not pulling in high enough when at idle? May not be working at all?

Not all aluminum radiators are created equal either. It is all about surface area and the size of the tubes used on the aluminum radiator. 4-core may actually be a restriction as most good aluminum radiators are good for high performance applications with only a 2-core. The 2 core can have a larger tube size, thus more surface area to cool versus a 4-core with small tubing. The stack of coring in a 4-core can be a restriction under low air flow circumstances, so you may need a fan that pulls a lot of CFM's at idle/lower speeds. This is what you can get from an aftermarket flex fan - much more CFM's at lower speeds but flatten out as the speeds increase. The downside, if it matters, is that these fans do make more noise, or a whirring sound, that some do not like.

You can test low speed air flow through the radiator by placing a piece of notebook paper on the front of the core and the fan should pull enough air through it to keep the paper stuck to and held onto the radiator core.

No mention of exhaust, or exhaust flow. Too small of an exhaust pipe or those super quiet restrictive mufflers can choke flow and cause heating problems, as can a stuck "butterfly" valve in the factory cast iron exhaust manifold IF so equipped.

May be the EFI air/fuel setting is too lean. Due to the extra oxygen in the ethanol molecule, you need more fuel and less air (generally richer-not leaner AFR) to achieve the same results. 91 octane E10 has a stochiometric ratio of 14.08:1 whereas non-ethanol would be 14.7:1. So the entire air/fuel range needs to be corrected. However, my example is for 91/93 octane and the factory 335HP engine shows to be 10.75 compression and may need more octane - but we did have a recent member/post who ran the lower octane by making timing adjustments.
 

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3. I had not thought of an engine oil cooler and like that idea very much. Looking into it!
Thank you. Much appreciated!
Cool oil is one of the best things that you can do for your engine. A cooler dramatically drops oil and engine temps, it adds life to the engine, and it speeds up oil changes, too! Plus you can do the remote filter mount and add the cooler in-line, which makes it all cheap, tidy, and now you can change your filter from under the hood.
 

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1971 GTO resto mod. Modified 428 HO, 4 sp (built by midwest muncie) Dana 60, 3.55 rear
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Pontiac Jim hit on a point I was just going to post about as I hadn't seen it mentioned.. AFR.. A lean motor will run a fair amount hotter..
An interesting article from Hot Rod Mag.. A HP Pontiac with a problem very similar to yours. One thing they did touch on was pulley diameter, as well as getting into the nitty gritty of cylinder head heat transfer, etc..
They do seem to be almost "advertising" for a liquid product even though this was a test and result, but still a lot of good info. I'm always leery of a manufacturer making "scientific" or "factual" statements as the bottom line is they are trying to sell a product. I always try to source 3rd party independent sources for any research and then compare to manufacturers claims.
Pontiac Engine Cooling System Upgrade - High Performance Pontiac
 

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I haven’t seen this in any of the previous posts. What about the lower Radiator Hose? Does it have the spring in it? Is it constricting at all when the thermostat opens? When hot, that lower hose can collapse very easily... just food for thought. Hope this helps.
 

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Good points, what I should have said is if the car was normally running cool,..and then one experienced it getting too hot at idle...a common problem.....not totally exclusive.....is a bad fan clutch or or air flow.

I think the OP never had this running cool ever, so your point is well taken and described. And yes retarded timing can make an engine run hotter.....But first all cooling system components must be right....advancing timing when other cooling system components are not right won’t do much.

A lot of these cars ran with retarded timing originally, with base at 4 or 6, for the purpose of burning off the NO at idle yet still would run within temp spec. Increasing the timing advance would make it run a bit cooler, but the retarded timing (as we see it today) will not spike the temp as much as a bad fan clutch.

lots to consider, and you need all things working together......
 

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Whew PJ take a breath you must have gotten carpultunal typing that...what a boatload of great information idk how you do it but kudos and to everyone else, that's why I joined...I have had temperature issues too and started buying into the keep the water in longer theory so I swapped the 160 high flow stat for a 180 high flow so do you think that will have any negative effects? My problem is always sitting still or moving really slow on a hot day.
 

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Hello! I know this topic has been discussed ad nausem but one more question, please. Car is 1967 400/335. Engine just fully rebuilt. Car ran hot before rebuild. Runs hot after rebuild. New 4 aluminum radiator. New EFI. New high volume water pump. Timing seems to be set optimally. Water wetter. Now that temps are getting warmer, runs hotter. At 55, temp around 210...but stopped at light or stop and go traffic, temp shoots up immediately to 230 or so....perhaps more but I haven't put myself in a position where it could. Electric fans didn't help. Tried various thermostats, didn't help. So, desperation. Has anyone tried waterless coolant like Evans? Any meaningful results? As always, thank you.
I just talked to an old friend back home today. He just installed a newly rebuilt 455 that previously ran hot in the same car. This time he had his OE exhaust manifolds Jet Hot coated. He said before and after temperatures are amazing! The Jet Hot coating keeps the outside of the manifolds 100 degrees cooler, directing the heat down the exhaust. This keeps the engine, engine bay temperatures radically cooler. I know it’s a pain to pull exhaust manifolds but sounds like this may actually help in the overheating issue.
 

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Also I can't believe you mentioned a model B 4 cylinder that's the car bug that bit me when I was 10 years old helping my dad take his apart for him to restore it, I think I still have Liquid Wrench embedded in my skin from 1975 ! He drove us to prom then I drove it for some weddings, it was the first stick I drove with my learners permit and I was scared to death when he pulled over and told me to drive. I had it freshened up a couple of years ago for his 82nd birthday and surprised him driving up to the house.
142357
142358
 

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Did you have the heads CC'd? My story on a 65 WS, the 77's had been cleaned up previously. My builder called me to say I need to clean up the heads again, you're going to be 11++ CR. I had him open the combustion chambers which eliminated the cooling and pre ignition I had experienced even with a re-cored Harrison to the max, Flo-Cooler w' matched plates, shroud, retarded timing, and electric fan. Make no mistake, I lost power. These cars won't stand up to a $12k 100k mi C6 vette which will leave you spinning tires at the line. Reality is today's fuels, and 93 octane isn't guaranteed. I am old enough to have enjoyed 260 Sunoco, but yesterday's gone.
 

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I had the same problem with my 65. Flow cooler water pump, big ass aluminum radiator, 160 degree thermostat and dual electric puller fans. This is a 40 over 455, with Butler 6x heads, about 9.5 to 1 compression. I have the fans set to come on at 180. Runs cool even on the hottest days.
 

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Ya that ship has sailed on coating the exhaust manifolds not removing them now, to bad I didn't hear about that idea before the motor went in sounds like it's a good idea.
 
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