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  #21  
Old 10-19-2006, 07:52 PM
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Quote:
Originally Posted by GMC Hauler
Be careful, it is not true that increasing the flow speed (or flow rate) causes overheat issues. This is contrary to the laws of thermodynamnics. The faster the flow rate, the more heat that can be dissipated.
True. Removing the stat removes the restriciton necessary for the bypass to work. Without the stat, unheated coolant get recycled through the radiator. This does not apply to all engines. Some are uneffected, others can be catastrophic. Depends on the cooling system design.
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  #22  
Old 10-20-2006, 08:35 AM
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D max
It has been proven many times that in automotive scenarios that the radiators, depending on their construction and "condition" will not respond to the faster is better theory. Many times with automotive radiators you cant get the heat to transfer from the water fast enough to be able to get rid of it.
I agree that if the heat is in the radiator fins you can blow it off, however due to the marginal sizes of vehicle radiators so many times you will very often surpass the optimum heat transfer time needed and the water will carry more latent heat back into the engine than if you run the flow a little slower to allow for better transfer.
This also does not even consider the condition of the core (Skunked up with crud that is insullating it)
** Under idea thermal conditions** but we dont ever have ideal in the truck world.

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  #23  
Old 10-20-2006, 10:09 AM
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I disagree, and so does thermodynamic law. I thought the same as you for a long time, and the results of my experience pointed to it. However, there is more to exchanging heat than just the radiator. The coolant has to pass through the radiator to be cooled. In many cases, including the 6.5, removing the stat prevents the bypass coolant from ever getting to the radiator. Also, there are other demons at play. Improper dynamic properties can also cause pump cavitation. Automotive water pumps are a very weak centrifical design. Their function is simple, but easily foiled.
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  #24  
Old 10-20-2006, 05:25 PM
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Cavitation can raise havock with the cooling properties by allowing a mixture of air to be whipped into the coolant forming an insulating barrier to the heat transfer.
I still maintain that too fast a flow will cause heating isses. I had a 76 Ford 3/4 ton 4x4 that I dropped a 427 cammer in. The radiator we installed was sized for the High compression engine and the extra heat produced over the stock 360.
I had a stat fail on the road and removed it. I had severe heating issues pulling the mountains and as soon as I replaced the stat all was well again. Now possibly it was a flow speed induced cavitation issue that caused it.
On the Ford FE engines the bypass may very well have been the isue. With no restriction it sure might cause a condition where the coolant never reached the radiator in sufficient quantity to cool right. HMMMMMMMM interesting.
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Last edited by Robyn; 10-20-2006 at 05:27 PM. Reason: spelling
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  #25  
Old 10-24-2006, 07:19 PM
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If the water is moving too fast through the rad to cool it down then couldn't you argue that uts moving too fast through the block to heat up?
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  #26  
Old 10-25-2006, 12:28 PM
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Food for thought... The LB7 & LLY Duramax use a water pump rated at 70-gpm - same as the original V-belt 6.2. However, even though the Dmax uses two thermostats, there are a litany of differences between the two cooling systems. Plus, the Dmax uses aluminum heads, which transfers heat at a faster rate than cast iron.

Otherwise, incidences of head cracking and temperature control are key indicators to know whether the 130-gpm/twin stats help or hurt the 6.5. In my opinion, there's no question the hi-cap cooling helps the 6.5.

Jim
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  #27  
Old 10-25-2006, 12:39 PM
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Quote:
Originally Posted by aloharovers
If the water is moving too fast through the rad to cool it down then couldn't you argue that uts moving too fast through the block to heat up?

Good one! If that were true, the engine would overheat but the gauge wouldn't show it!

Fact is, the engine will transfer heat to the water based on the temperature difference between the two. The speed of the water through the jacket is irrelevant. Lots of little buckets of heat is the same as a few big buckets, if you will. If enough heat cannot be transfered, the engine temperature increases until the transfer rate increases enough to handle the load. If this did not happen, the water temperature, as indicated by the gauge, would not change even as the engine got hotter and hotter.

Pumping the water faster makes the temperature throughout the system more uniform. (Bypass issues asside...) The temperature will be higher at some points and lower at others. Desireable? Maybe, maybe not.
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  #28  
Old 10-25-2006, 03:31 PM
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For any radiator system there is an optimal time that is required for the coolant to give up its heat to the tubes and then the fins so it can be wasted off with the passing air. If the radiator will not conduct the heat as fast as the water is moving through you are operating beyond the radiators
limits and the heat will continue to build to a point.
Now if the heat build up cant be wasted off to atmosphere you are done.
Let say that normal flow through the radiator is 70 GPM and we suddenly try to flow 200 GPM the time it takes for the heat to transfer will not be sufficient and the coolant will pass right through without giving up the needed heat.
Increasing the size and heat dissipating capacity of the radiator will solve this issue.
This is why the two row radiator in a truck with a V6 will not cool a 454 monster.
The radiators capacity to reject heat is not there and I dont care how fast you try and pump the water through its not gonna do it.
More flow more core real simple
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  #29  
Old 10-26-2006, 09:23 AM
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One thing I can say with complete conviction: at least one of us is wrong.

Step in if you think this is wrong.

From what I think you are saying, speeding up the flow of water through the radiator somehow negatively impacts the ability of the coolant to transfer heat to the radiator. If we carry that concept to its logical conclusion, it would seem that as we speed up the flow the, coolant temperature would go up and the temperature of the radiator would go down.

Similarly, increasing the airflow over the radiator would negatively impact the transfer of heat from the radiator to the air, so, it would stand to reason that engaging the fan clutch would cause temparatures to climb. (Maybe this is why my '95 ran hotter when I drove faster... )

Don't get me (completely) wrong. I'm not saying the phenominum (sp?) doesn't occur, just that the reasons presented in "common wisdom" do not account for the effect.
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Last edited by JohnC; 10-26-2006 at 10:02 AM.
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  #30  
Old 10-26-2006, 04:04 PM
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I can help settle the argument...

I understand what robyn is seeing. She is just misinterpreting the results.

Fluid flow is no different than basic electricity.

When you use a 4 core raditaor, the resistance is basically cut in half, and more mass flow through can be achieved through the radiator (about double).



Lets use Ohm's Law. V = I x R

Where V = voltage (or outlet pressure of the water pump)
I = Current (or mass flow rate of the liquid)
R = Resistance of the component (or resistance to flow from the radiator)

Lets assume that a 2 core radiator has a resistance of 2 ohms, and a 4 core radiator has a resistance half of that, 1 ohms.

Lets also assume that:
1 gallon equals 1 volt.
87 GPM is the stock water pump max flow rate.
130 GPM is the stock water pump max flow rate.
There is no thermostat.

So...

Reconfigure ohms law to: V/R = I

We really want to know what I is (mass flow rate through the radiator).

Stock Radiator:

87/2 = 43.5 (stock water pump, 2 core radiator)

87/1 = 87 (stock water pump, 4 core radiator)

130/2 = 65 (hi cap water pump, 2 core radiator)

130/1 = 130 (hi capacity water pump, 4 core radiator)

As you can see, you get more flow through the radiator with the stock water pump and the 4 core radiator. The most flow will come from the high flow pump and 4 core radiator.

Lets reverse the use of the formula. What would have to be the rating of the water pump in order to achieve the 130 flow rating through a 2 core radiator:

V = I x R

V = 130 x 2

V = 260.

Your water pump would have to work very hard to achieve this. Without getting deep into pump law theories here, as you double flow, you quadruple pump head (or pressure out of the pump) and raise pumping power requirements to the power of 3. When you raise pump head, you are raising pressure out of the pump. Rememebr, John Kennedy has stated that sometimes when people run the hi flow water pump without the dual thermostat crossover, freeze plugs can pop out. This is why.

I know, someone here might say that I should have used the GPM rate for "I". Without knowing the pump curves, I worked backwards basically. The results are the same.

The 2 core radiator's "resistance" is to high, therefore when you try to apply a 200 GPM flow rate, it will never achieve it.

Now, without getting deep into heat transfer dynamics and equatiors, when you increase mass flow rate, you increase the amount of heat that can be transferred from one device to another. Slowing down flow to increae heat transfer rate violates the laws of thermodynamics, plain and simple. To bowwor a phrase from Scottie on Star Trek, " I cannot change the laws of Physics Captain".

The reason that the 2 core radiator will not cool the big block is that you can't readily achieve 200 GPM through the 2 core radiator with any reasonable water pump.


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  #31  
Old 10-26-2006, 05:13 PM
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Quote:
Originally Posted by JohnC
One thing I can say with complete conviction: at least one of us is wrong.

Step in if you think this is wrong.

From what I think you are saying, speeding up the flow of water through the radiator somehow negatively impacts the ability of the coolant to transfer heat to the radiator. If we carry that concept to its logical conclusion, it would seem that as we speed up the flow the, coolant temperature would go up and the temperature of the radiator would go down.

Similarly, increasing the airflow over the radiator would negatively impact the transfer of heat from the radiator to the air, so, it would stand to reason that engaging the fan clutch would cause temparatures to climb. (Maybe this is why my '95 ran hotter when I drove faster... )

Don't get me (completely) wrong. I'm not saying the phenominum (sp?) doesn't occur, just that the reasons presented in "common wisdom" do not account for the effect.

Not to speak for anyone here, but I think the point that Robyn's trying to make is that heat transfer is a function of flow rate, surface area, and time (coolant temp, ambient temp, & humidity factor into this too but let's keep it simple LOL.) If any one or more of these factors is out of balance with the others, optimum heat transfer won't take place. Too small of a radiator and there's not enough surface area to transfer heat. If you push the coolant through the radiator too fast it won't be in there long enough to transfer as much heat as the radiator is capable of transferring.

And yes, I think that if the coolant can get out of the block too fast it won't pick up as much heat and therefore the engine can overheat even though the coolant temp gauge reads OK. I've seen way too many people remove thermostats and immediately start having overheating problems - that were cured when a stat was reinstalled - to believe otherwise.
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  #32  
Old 10-27-2006, 10:57 AM
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Quote:
Originally Posted by NH2112
... If you push the coolant through the radiator too fast it won't be in there long enough to transfer as much heat as the radiator is capable of transferring...
This is exactly the issue. Time is only relevant if we look at the heat transfer from a particular "bit" of coolant. It doesn't matter if we pump 2 gallons of water through the radiator in a minute and each gallon gives up 1 BTU, or pump 1 gallon through and that gallon gives up 2 BTU's. The same amount of heat is shed either way. The purpose is to take heat away from the engine, not to cool the water. Take care of the former and the later will take care of itself.

Actually,if you slow the flow down, transfer efficiency suffers because the temeperature differential between an increasingly larger part of the radiator and the ambient air gets smaller. You're trading cooler water at the radiator outlet for hotter water at the inlet. Faster flow = more even temperatures.

Removing the thermostat does more than just change the rate of flow through the radiator. If problems occur, the other issues are at the root.

BTW, if you could cram 200 gpm through that 2 core radiator, the cooling system would work fine.

(Surface area is a different issue, separate from the one we're adressing here)

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Last edited by JohnC; 10-27-2006 at 11:42 AM.
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  #33  
Old 10-31-2006, 10:33 PM
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Without boring anyone with thermodynamic formulae, the radiator doesn't know what's going on. Unless the radiator is grossly undersized, the higher capacity cooling system (and here I refer only to the 6.5L TD with the Kennedy kit, with which I'm familiar). Recall the comments about the "flow through the radiator is increased only 7% while the flow through the block is increased 40+%".

The radiator has a finite heat transfer ability. If it's of sufficient capacity (meaning transfer area) for the engine, it will have a great deal of reserve capacity. Now as to the flow through the block, the coolant is picking up only a certain amount of heat per cycle. If the flow is greater, the amount of heat absorbed is just about the same, but the temperature of the coolant will not rise as much.

But the thermostats come into play here. Flow will be adjusted by the thermostats, so in actuality, the flow through the rdiator will be roughly the same unless the engine is highly loaded, in which case (with the thermostats both wide open), more heat will be transferred by the radiator and not built up in the block as opposed to the 90 gpm pump and single thermostat.

It's only at extremes of engine output that the benefits of the hi-cap cooling system actually come into play; it provides a reserve not present with the stock system.

Where I notice it on my 16K lb. motorhome is that on a long grade pull, temps climb to about 205-210
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  #34  
Old 11-01-2006, 10:22 AM
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Good Day!

Boy, this topic is turning out to be just what I had hoped - a good no-nonsense technical discussion. Thanks to all.

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  #35  
Old 11-02-2006, 01:48 AM
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Default Why 180 thermostats, then?

This leads me to ask why people like to put 180F thermostats in their cooling systems? Since the radiator cools more effectively with a higher delta T, doesn't this prematurely rob the cooling system of it's optimum effeiciency, which, I'll assume was designed in by GM originally for the factory stock 195F (or is it 205F?) T-stats?

I realize that there are 2 deltas at play; engine -> coolant, and coolant -> air (through radiator), but given that cylinder wall temps will be as high as 400F or more, finding a spot closer to the mid-point between 400 and ambient (say 100F) would seem to be a better fit.

Or is 195F just better for emissions only and at the expense of better cooling that could be obtained with 180F?
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  #36  
Old 11-02-2006, 07:49 AM
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Good question, Michael.

The 6.2/6.5 operates most efficiently with 195
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  #37  
Old 11-03-2006, 02:56 PM
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Exactly. The thermostat sets the low limit. Stress the system and the temperature climbs until the delta T allows the radiator to shed the BTU's or the system boils over...
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  #38  
Old 06-15-2007, 10:11 PM
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Lightbulb h**** diesel just came out with a new system...

I guess the single 180 stat,marine pump,cooler clutch with the dmax fan must be the ticket on keeping it cool. As We now when he comes out with a setup it must be great.
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  #39  
Old 06-16-2007, 09:23 PM
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Quote:
Originally Posted by Michael Prichard
This leads me to ask why people like to put 180F thermostats in their cooling systems? Since the radiator cools more effectively with a higher delta T, doesn't this prematurely rob the cooling system of it's optimum effeiciency, which, I'll assume was designed in by GM originally for the factory stock 195F (or is it 205F?) T-stats?

I realize that there are 2 deltas at play; engine -> coolant, and coolant -> air (through radiator), but given that cylinder wall temps will be as high as 400F or more, finding a spot closer to the mid-point between 400 and ambient (say 100F) would seem to be a better fit.

Or is 195F just better for emissions only and at the expense of better cooling that could be obtained with 180F?
180's will allow the engine to put more heat into the radiator a little sooner than it would with 195's. In turn, the fan-clutch will engage a little sooner. This could allow some stock calibration clutches to engage when they should (or at least soon enough to help prevent an overheating problem). Plus, a 15-degree lower average engine temperature should produce a positive benefit for the DS4 electronics.

To use the Duramax analogy again.... it uses a pair of t-stats with staggered temperature ratings. The lower is at 185 degrees.

See a related thread on this subject.

Jim

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