Another Overheating Question.....A long Post

[mraley]

This may be long winded, but I really some comments on this one. I think most of you have seen my Mustang and dyno pulls from previous posts. What I need to know is how many of your engines are bored 60" over and what kind of cooling system are you running?

The reason is an overheating issue. When I started my rebuilding process a year or so ago I was running hot all the time. We installed a new radiator and the problem was corrected.

Then, I added an aftermarket AC with the condenser mounted in front of the radiator and my gauge moved a little more toward the center. Still no issues.

Next, we rebuilt the tranny and did the high stall converter. I was told that It may make the car run a little hotter and that I may want to install a separate trans cooler. I didn't really notice any change in the position of the gauge so I didn't really worry about that.

Now, I'm starting to notice that once I get up to about 70-75 while cruising the interstate my gauge moves further towards the "Hot" mark. It has never boiled over but is almost past the normal operating range and only goes back if I slow down to 55 or 60. I haven't really started driving the interstates until spring of this year. We all know Texas has some hot summers!!!

I bought one of those laser gauges to check the accuracy of the Temp Gauge and found that dead center is 195 while cruisng around town at slower speeds. I stopped my the local Mustang supplier and was looking for a fan shroud thinking that it may help redirect the air at highway speeds. Well, the first question he asked me was........"Are you bored out 60" ? ".......And of course I answered yes. He proceeded to tell me that our sixes are not meant to be bored more than 40 over, or the overheating occurs at highway speeds. Furthermore, the only way to correct it is to yank out my 3-Row Radiator and go with a Cross Flow Aluminum Radiator and still no guarantees that this will solve the highway issues!!!!!

This conversation went on for about 30 minutes about how bad a mistake it is to over bore our engines and in the end would not sell me a shroud be he could guarantee me it would not help cool the engine at highway speeds. He claims that he seen several of these engines with the exact problem.

In addition to the 3 Row Radiator I have one of those Flex Fans that is about 15 inches across and had 6 blades. I can sit and idle all day and never go past 195 with the laser guage.

Any thoughts on this one??????? My mechanic says as long as it doesn't boil over it ain't hot!!!! According to my calcualations when the needle move almost to Hot I'm running about 240 degrees...Yikes!!

This just doesn't seem right.....Help!!!! Michael

 

[MustangSix]

I really don't think .010" of iron makes much of a heat shield, so as far as I'm concerned, boring .060" is no worse than .040" when it comes to heat transfer.

Based on the fact that it's creeping up at highway speeds, I think the first thing you should check is the ignition advance mechanisms. Inspect the mechanical and the vacuum to make sure its advancing, otherwise it can contribute to heat load when the engine is trying to produce power. This very same flaw is what has killed more Jaguar V12 motors than anything.

Inspect the radiator itself to make sure there is nothing blocking coolant flow. You may have dislodged some crud over time and it could be cutting the flow of coolant. Again, adequate to idle, but too little for high speed.

One other thing that may help is a Shelby style valence. If you notice, half your radiator is blocked by the front end sheetmetal. Shelbys removed this to expose the lower portion of the radiator and gain extra cooling at speed.

The Afco or Speedway Ford radiators will fit into an early stang with little effort if you find you really need a more efficient radiator.

 

[mraley]

MustangSix.....Thanks, I hadn't thought about the "Shelby Style" valance. That would be a nice addition for later in the year after the car show season is done.

We checked the radiator flow. No gunk, and clean as a whistle.

As far as the igition advance mechanisms, I running a recurved Durspark dizzy that I got from Scott at Reincarnation...I'll check on that...Thanks

 

[Anonymous]

my 200 is bored 60 over and it has the opposite problem, runs cool on the highway but get up there at idle. I just bought a 3.5" shroud which I hope will help. I also have a 3-row radiator and a flex fan and AC.

Have you checked that your lower radiator hose does not collapse at higher RPM? The replacement hoses don't always have the spring in there that holds it open, or they rust out. I had a problem with this a long time ago when the motor was 30 over.

According to the machine shop, they make 80 over pistons for the 200, so he figured 60 was safe. But it definitely runs hotter now.

I don't know what the wall thickness is, but if the wall is .1 thick, taking off an extra .01 means 10% more heat flow from the cylinder to the water.

 

[mraley]

SixPacker...I forgot to mention..I'm running Coolflex hoses..You know the ones made from corrugated copper with chrome on top...Suppose to work better than regular hoses, not mention they look sharp!!!! I don't think they can collapse.....Glad to hear your not running hot on the road. It's got to be a simple fix..Just got to figure it out. Thanks, Michael

 

[addo]

I think the most likely cause is a still body of air at the nose that increases in size at the problem speeds; effectively blocking radiator airflow.

Then there's weird stuff; block and head flaws, water pump effectiveness changing with speed (could it be cavitating?), maybe even a part of the fuel curve that runs leaner.

You could try louvring or slotting generously on both sides of the number plate, avoiding the Shelby look that way. Knowing your A/F ratio at the overheating conditions could be interesting, too.

Cheers, Adam.

 

[t-west]

The guy at the local speed shop tried to sell me an 2 row aluminum radiator over my three row. They are the same depth (though not the same price). He thought the three row was bogus because, to paraphrase, the middle row heat ain't got nowhere to go.

So many people are running three row radiators, yet I had to wonder.

Just a thought,

--tom

 

[MustangSix]

It has to do with surface area. Typically, the more rows you add to a radiator, the more surface area you gain. There is a limit to this, however, and a four or five row brass and copper radiator is usually no more effective than a three row because you can't move enough air over the tubes.

The aluminum radiators are designed differrently than the brass/copper ones. The tubes are large 1" wide ovals and even though they are usually only a two row, the surface area and airflow are maximized. Some of them are only one row to save weight. Even though aluminum is less efficient at transfering heat, the increased area and airflow makes them more efficient.

Boring increases heat transfer by increasing surface area, but thickness has little to do with heat transfer rates thru materials. It all boils down to (pun intended) the ability of the system to move that heat from the cylinders, to the coolant, and into the air. The total amount of heat produced is dependent on power produced, so your total transfer capacity has to at least match that.

 

[mraley]

Hey..I haven't heard from many of Y'all....Just curious, How many of your 200's are bored 60" or more without any overheating problems?

 

[grocery getter]

if it's lean it can cause it to run hot

 

[MustangSix]

The crossflow in the Mustang is bored .040 over.

 

[Anonymous]

Mines bored .060 over and I'm running a late model water pump which is supposed to flow more than an early model one.

Works fine for me!

Doug

 

[Anonymous]

"thickness has little to do with heat transfer rates thru materials"

I don't agree. If you want to pick up something hot would you rather have a paper towel or a thick rag?

The inside of the cylinder is hot, the water is cool. The cylinder wall insulates the water from the heat in the cylinder. The thinner it is, the less it will insulate.

Iron is a lousy heat conductor. I experienced this first hand when I was bending my carb linkage. I used a torch to heat it up red hot and bend it. I started out with heavy leather gloves, but soon found that the rod was cool except for right where I applied the torch.

 

[MustangSix]

"thickness has little to do with heat transfer rates thru materials"

I don't agree. If you want to pick up something hot would you rather have a paper towel or a thick rag?

The inside of the cylinder is hot, the water is cool. The cylinder wall insulates the water from the heat in the cylinder. The thinner it is, the less it will insulate.

Iron is a lousy heat conductor. I experienced this first hand when I was bending my carb linkage. I used a torch to heat it up red hot and bend it. I started out with heavy leather gloves, but soon found that the rod was cool except for right where I applied the torch.

You're talking about the thickness of an insulator. The cylinder wall is not insulating the coolant from the heat, it's transferring it. Would you rather grab a thick wall cast iron pot of boiling water or a thin wall one with your bare hands? That depends. Did you just put the water in the pots or has it been sitting in there for a couple of minutes? Once the pot reaches stability, the heat still gets transferred to your fingers at the same rate.

You do have a point about one thing and that's the initial rise in heat. Heat and temperature are not the same thing. Heat is the energy stored within a mass, temp is the relative difference between two masses. It takes longer for heat to build up in a larger mass of iron than a smaller one.

But once a stable temperature is reached, the material properties will govern the rate of heat transfer between two materials, in our case iron and coolant. An increase of .010" in the thickness of the material is going to have a negliglible effect in that transfer rate. Even though the engine is undergoing cyclic heat load changes because of combustion events, the process is relatively stable.

Here's a good analogy. I think Smokey Yunick used it first. Let's say heat is like a swimmer in a pool and the width of the pool represents the thickness of the cylinder wall. The longer the pool, the longer it takes for heat to get from one side to the other. But in an engine, you don't have a single swimmer. You have a continuous flow of them in single file, representing transfer at a certain rate. Once the line of forms the rate is constant and continuous. By making the pool shorter (thinner wall), the first swimmer gets there sooner, but the line moves at the same rate after that. I'm sure Smokey said it better.....

 

[Anonymous]

I have heard about not boring out to .060" in Argentina too. Apparently, Ford solved the problem for the TC racers by making special "heavy" castings of the 188/221 block. Some of them were fitted to production engines.
I will try to investigate about the heat transfer issue, but there's other problem that could arise. The walls can get so thin that the bore distortion will become a problem, killing the power gain from the extra cubes. Sonic testing is the only way I know to be safe.

 

[Anonymous]

The typical reason that bored out engines run hotter is that the compression ratio is usually increased if the piston configuration or combustion chamber is not modified to maintain the same compression ratio. Making the cylinder wall thinner is not going to significantly make the cooling system hotter. As Mustang Six stated, once the heat flux rate is established, the system seeks equilibrium.

If the Coolflex hoses have a corrugated inside diameter as opposed to a smooth inside diameter, then I fail to see where that will help cooling. Corrugated hoses will have more friction which would decrease the flow rate of the circulating coolant. I doubt that it would be that significant in these applications, but I can't see why it would be better unless the heat radiated by the metal hose is greater than any reduction in heat transfer due to the associated reduction in flow capacity.

Mraley, you mention that you calculated the 240 deg hot temperature. If that is based on the 195 deg reading at the center of the gauge, it may not be correct. An electrical engineer on a Corvette forum has mentioned several times that the temperature sending units are not linear in response, meaning you can't necessarily interpolate/extrapolate the temperature readings with any accuracy. He explains that as the sending unit heats up, the electrical properties of the unit change non-linearly due to the the heat changing the electrical resistance etc.

Despite what the guy behind the counter said, a fan duct should help somewhat, but I would look at the timing advance and carburetion first.
Are you running a vac advance?
Doug

 

[Stubby]

I would verify a/f ratio then play with timing and see if I could make a difference. If these don't make a difference I would consider the pump and thermostat. I have seen some strange thing happen with waterpumps and thermostats. They don't all flow the same. I had a customer with a prostreet 56 Ford truck with a 460 who kept blowing freeze plugs at the top of second gear. While trouble shooting it I learned alot about cooling systems. It had a plug in the coolant passage before the thermostat, I installed a pressure gauge and it had up to 105 psi with the thermostat closed and 85 psi with it open. It had a huge beautiful brass radiator and the engine was getting alot of fresh water and the thermostat was closing about the top of second gear and poping a freeze plug.

I ended up drilling four 1/4 in holes in it to lower the open pressure to 85 psi. The thermostat functions as a restrictor to raise the pressure and boiling point on the backside of the combustion chambers and cylinder walls.

 

[mraley]

66 Fastback 200....I'm not for sure about the Vac Advance. I can't remember how we set the Duraspark II system up. I know I had the Dizzy recurved from Scott At Reincarnation. This gives me something else to check in to....



Stubby.......I'm going to check on the water pump. Somebody else in a previous post mentioned buying a later water pump that was designed for AC Systems. When I replaced mine last year I think I just got the stock one for the 66 200 w/o AC, since I didn't have a AC unit at the time.
We are going to play with the carb next week and make some changes there.

Thanks for all of your advice....

Southern Cross Racer...I would be interested to see what you come up with if you do some more research on this one...Thanks

 

[Anonymous]

This is a good discussion. I've never seen a satisfactory explanation of why an engine over heats when it's bored too far. I've been thinking about this heat transfer issue since 2001 when I had a 60-over 289 which would pump the water out the overflow valve any time I revved over 4000 RPM, whether it was overheating or not. I mean it would empty the radiator. High pressure radiator caps, Redline water wetter, nothing helped. I finally fixed it - turned out all it needed was a new block!

I think of it this way: The gas in the cylinder is sitting at some average temperature, I would guess 800 F. (It goes up and down with the intake and power cycles, but I assume that the cylinder wall will not heat and cool that fast and we can just think about the average.) The water is sitting at around 200 F. Heat will flow from the gas in the cylinder to the water at a rate which is the delta T divided by the thermal resistance. Thermal resistance has the units of deg F/Watt. The thermal resistance is calculated from the material thermal conductivity, the cross sectional area and the thickness. More area increases the heat transfer, while greater thickness will reduce it.

That is why you put thick insulation in your house, and why a big house costs more to heat than a small one.

Insulation and conductivity are really just two sides to the same parameter. One is the inverse of the other.

 

[Anonymous]

Sixpacker,
When you went to a new block was it also 60 over too? If it was not the same bore and compression ratio then that would probably explain the difference. Also consider that the old block likely had scale build up on the water jacket. Films and scales on the surface of the metal affect the heat transfer more profoundly than a minor reduction in the thickness of the metal.

A third possibility of the old block is that you could have had either suction problems or cavitation of the pump occuring at elevater rpms that would reduce the circulation rate of the coolant and allow the coolant in the block to overheat and belch out the cap.
Doug