PhillipM

No, if it's flowing faster it will take more heat out of the engine leading to a higher delta-T at the radiator, even if the coolant comes out of the radiator so fast that it's at a higher temperature than if it were going slower, it's carrying heat out of the engine much faster so the net cooling is higher.


Basically, you want the radiator as hot as possible to get the maximum temperature difference between it and the cooling air in order for it to remove as much heat as possible - faster coolant flow results in a cooler engine and a hotter radiator, it equalises the temperature between them better.

olddragger

iTrader: (3)

I like how you said that " hotter radiator , cooler engine". That sums that point up nicely.

For those just joining this thread--remember its the cooling of the engine's metal that is the key. Never focus on just the coolant temperature, although it is related, it doesnt tell you all that you need to know. Sort of like the Girlfriend that tells you the "truth" but leaves out one or two "details"!

Yall know that this is leading up to a thing I am gathering data on? That our water pump is not flowing well enough under 2.5K rpms?
There is only one overdrive water pump pulley out there............

Charles R. Hill

iTrader: (7)

Heat developed in the combustion chamber is transferred from the chamber, through the metal of the engine, into the liquid cooling medium, then into the metal of the radiator core, then the air which moves through the radiator, and out to the atmosphere. (Of course, there are some other ways in which heat escapes the engine but those ways are not the primary sources of cooling so I am not concerned with them right now.)

Each one of these transfers of heat takes time to accomplish, based on many factors (including density), and the question germane to this discussion which needs to be answered is; how much time does it take to transfer the heat from the water/coolant to the radiator core?

If a given volume of water/coolant passes through the radiator core faster than that volume's own ability to transfer the heat which it carries to the radiator core, the efficiency of the cooling system will be compromised.

Charles R. Hill

iTrader: (7)

Not exactly. One would optimally want the coolant entering the radiator to theoretically be as hot as possible (carrying more BTU's, actually), and the coolant exiting the radiator to be the targeted operating temperature of the engine. This paradigm would ensure that as much heat as possible is being carried away from the engine while also ensuring that the targeted engine temps are maintained. The reason we have thermostats, water pumps, and fans is because there are environmental/contextual variables which are being accomodated through those devices.

PhillipM

That's pretty much a function of making sure the radiator area/efficiency is high enough though, rather than coolant flow speed.

paimon.soror

iTrader: (15)

you guys are forgetting one of the most important parts of cooling efficiency. It has less to do with flow, more to do with turbulance. Forgetting the fact that this is a closed loop system, ideally the mains of the cooling system would have laminent (read:without turbulence) flow, especially where moving parts are concerned, ie the water pump. In retrospect, an efficient cooling mechanism would have turbulence. Turbulence is what makes sure that every molecule of water gets heated evenly as it flows through the system. Leaving your cooling system with significant laminar flow, coupled with an increase in your flowrate vastly degrades the systems ability to carry and dissipate heat.


Thermo/Fluid Dynamics ftw

ASH8

Precisely, and if Air Flow through Radiator/Cooler is also restricted by either..
Blocked (bugs-dirt) or bent core fins.
Slow running Fan Motors/Fan Blades.
Extreme atmospheric temps.

The cooling system is even more compromised and is often overlooked by some owners.

Easy_E1

iTrader: (2)

Only problem is that you want the coolant (flow/GPM) to pass through the radiator at a speed that allows the coolant to be able to dissipate the most heat in the time it travels through the radiator. This can vary with the size of the radiator.
So faster is not always the answer.
You can run coolant through a radiator and it's traveling so fast (GPM) that it has no time to utilize the effects of the radiator. The radiator can remove just so much heat per GPM flow. Based on surface area and air flow. Size.
In other words not all the heat that can be removed from the coolant is being removed. It's passing back to the engine core.

So you want the coolant to spend the most time it can in the radiator to displace as much heat as possible out of the coolant through the radiator. Thus it can absorb more heat from the engine core. Sending it to the radiator to be displaced.

Increase in GPM? All your doing is sending the heat back into the engine. Pretty soon. Heat soak. Overheating.
Mazda's issue with an undersized radiator from the factory.

Flashwing

This question is the heart of the goals when it comes to cooling the vehicle and why the thermostat might be the incorrect place to attack any cooling issues. The reason being is, assuming proper operation, the thermostat is fully open way before any potential heating issues take place.

I understand the idea is to get a head start on cooling by providing radiator access to hot coolant before heat becomes a problem. The issue I see with that is you're simply buying yourself time before an overheating event takes place.

The temperature delta is the primary focus and the thermostat does nothing to address that issue. The thermostat works to maintain equilibrium at a specific operational temperature but once the thermostat is fully open it no longer enters into the equation.

You won't increase the temperature delta by exposing coolant to the radiator sooner. You address the primary cooling mechanism and increase its efficiency in the ranges which require it. This means increased surface area, or materials/fluids/methods that obtain and shed heat faster.

olddragger

iTrader: (3)

the ideal system would have a computer controlled thermostat, electric water pump and fans that could respond to the changing needs in the engine and environment. Its a system that could be made but it is probably not worth the time or money.

The engine is never at an equilibrium in regards to its cooling needs. RPM's and Loads are always changing. So it would be wise to maximize the responsiveness of the system as it will always chase temperatures due to the engines changing needs. Increasing flow allows for a faster response in cooling the metal. The thermostat will govern the flow as needed.

Easy- i disagree on that belief that the coolant has to have a certain period of time in the radiator. Look at some of the thermodynamic principles involved with heat exchange and see if they make sense to you?

With our system you cannot get the coolant to flow to fast. If you somehow do get the system to flow coolant so fast, beyond the physics/thermodynamic non linear benefits, then it is time to start worrying about erosion.

Now for those of us that are using Evans coolant ( or thinking about it) the flow rate of the coolant becomes more important. Evans ( actually nothing liquid that we can use in the engine) cant absorb as much heat as water so others principles of cooling become more important.
For example , adjacent to the metal surface there is a slow velocity film of coolant irrespective to the average flow velocity. Increasing velocity decreases the thickness of this slow velocity film which increases heat conductance. Since Evans does not absorb heat as well as water it will be of benefit to increase the flow to help increase heat conductance.
OD

Mazurfer

You forgot old worn out coolant, partially collapsed hoses, and a few others.

Don't get me wrong, It is in the Tech garage and I'm glad Denny is out there and has the time to come up with all these ideas, pursue them, and start informative or thought provoking discussions.........just sometimes I think they are based on "in an otherwise perfect world" and we overlook the obvious things for the average Joe first.

Guess this plays of the "Minutia" comment from above.

There, and I contributed nothing of any real relevence to the entire discussion as everything for the most part was already being said.

Charles R. Hill

iTrader: (7)

I was pointing out that if someone is going to start playing around with the water pump's flow volume they better know the rest of the variables in a given cooling system, one variable in particular in this case, that they are dealing with when doing so.

olddragger

iTrader: (3)

absolutely. I totally agree. I know you did a lot of stuff in going up with the correct aftermarket radiator and that is the what you have to do. There will always be a beta tester due to variables--but homework is very important.

I think one thing a lot of people take for granted for example, is the radiator cap. If they are off by 2-3lbs it can really affect the metal temps. The operating range of normal antifreeze solution critically depends on a correct pressure from the radiator cap. I have a friend that ruined his engine by running just one track day session because he forgot to replace his radiator cap. His temp gauge was showing borderline temps of 220-230F but his engine was frying. Ambient was about 100F that day. It was a turbo rx7.

Mazurfer you are right that most theory is associated with controlled conditions, the perfect world you mention. Thats where field testing comes in, isnt it? I have been a Guinea pig a lot of my life
.
Our cooling system is a closed loop system that responds in a variety of ways according to the needs of the engine. Coolant flow is but one of them. Actually if you think about it, we have two cooling systems not just one.

ken-x8

Did he leave the cap off, or did he have a cap that was not the right pressure?

The pressure cap pretty much sets the temperature at which the coolant will boil. Until that point, it's not going to matter. Once it does reach that point it does matter.

I trust that when you finish this mod you'll choose a thermostat whose full open flow area is the same as a stock thermostat's flow area.

Ken

ASH8

Agree Dave...

Mazda and every other manufacturer make their cars for all markets, very rarely will you see a different Thermostat, or Radiator for a different region/country, they just don't do it.

One for all and all for one.

One thing which definitely concerns me with the S1 RX-8's are the Fan Motors, if you are doing a lot of stop and go (traffic lights) use in hot weather, I am certain by now that these old OEM Fan Motors are not spinning at optimum RPM.

If you can hear a loud or high RPM externally of your cooling fans (with air con off) then I strongly suggest you look at your motors...remember you have 2 speeds, if low speed is not going fast enough (due to motor wear), coolant temp rises and high speed starts up.

#1 Fan Motor 8.9 -11.9 AMPS
#2 Fan Motor 4.0 - 7.0 AMPS

Verify that each fan motor operates smoothly at the standard current.
Renew Motor(s) if any malfunction.

olddragger

iTrader: (3)

Good points Ken and Ash

Concerning the thermostat , the barrel type has a larger open area when it is fully open.
Rough estimate guess is 30% bigger. Its a 180F. So thermostat resistance should be greatly reduced.
Heres a statement about the one I am using "High-flow thermostats from Milodon greatly aid the correct functioning of a high-performance cooling system. They're engineered to warm the engine to a proper operating temperature without making it run hot enough to lose power. Also, the "Balanced Sleeve" design equalizes the pressures exerted on the thermostat. This counters the undesired effect of increased flow from a high-volume water pump, which actually tends to hold a stat closed."

About the Rx7--the cap was on but they forgot to tighten it--so it was just in there--no seal whatsoever.

Ash I have already solved the fan problem by wiring the fans in parallel when I installed a flex a lite variable speed controller. Its a sweet unit with many features and the parallel wiring made a big difference on my car during in town driving.

One other thing I have observed is that our by pass system also progressively opens/closes.
This means with the oem thermostat and coolant temps at 180F the bypass system is still flowing some. I really do not like that.
I suspect that even when fully closed there is still some leakage going on.

TeamRX8

iTrader: (25)

It's really no wonder you are still struggling with the same overall issue after so many years .... the number of inaccurate assumptions and comparisons being made is mindboggling

ken-x8

That's equivalent to a 0 psi cap, which is a lot more extreme than the 2 or 3 psi difference you cited as being a potential problem. And cap not tight is likely to cause problems with just about any car.

IMHO, for street use the fans are the weak spot in the 8's cooling system. Just an observation from the way the air conditioning stops putting out much cold air when stopped on a hot day, but resumes once moving.

Ken

1.3_LittersOfFurry

iTrader: (4)

Why not rewire the fans to come on sooner? I havnt seen my coolant temp above 195*f the entire summer with using the a/c and in stop n go traffic. I use "minds eye engineering" cooling fan rewire kit. My fans come on around 185* and turn off at 181*. No complaints on a/c output while stopped either.

9krpmrx8

iTrader: (46)

Fixed. Cobb AP FTW.

ken-x8

Since I just have the factory gauges, I don't know what my coolant temp actually is when the AC stops flowing. I was slow on learning what the factory temp gauge shows. I need to get a scangauge or similar next summer so I can keep track. If I see a frequent problem, I'll look into rewiring.

Has anyone ever put in a manual override for the fans?

Ken

1.3_LittersOfFurry

iTrader: (4)

9k, Yea, I didn't know about Scott till long after I bought stuff from him. It's the only "kit" I know of too. Unfortunately, I have other things on my list to get before the AP, like some new shocks. I do want one, but It has to wait for now.

Ken, you can rewire the fans yourself, after installing the fan kit I saw how they operate. If you run a ground wire with a switch to the negative contact points on 2 of the fan relays you can have 100% control of them AND they will still come on when the ECU tells them to (for a/c or coolant temp). I would gladly share anymore info I could give on it, if you would like.

olddragger

iTrader: (3)

My fans can come on at any temp I want with the flex a lite vsc--i currently have them set at 185F. They come on 1st at 60% and the controller has a soft on feature. Its the paralleled wiring that causes both fans to come on together and that has made a difference for me. It also has an A/c activation function and a manual on and off ability.

The rx7 example was the extreme version. Is anyone saying that the lost of 2-4 psi from the radiator cap will not make a difference in when the coolant will boil at the metal?

Mark--I am just trying to learn. If I have interpreted something wrong or if I am over thinking something, let me know? I see something that may be a little improvement that as far as I can tell, no one has done before on this car and I am willing to try it. Much like yourself when you went with Evans?
Its true that I am not able to formally present the effects ( good or bad) concerning this little modification, I can only give an opinion and my experience and others can take it for what it is worth.
I know it is not going to be a modification that is going to make a tremendous difference in how the coolant system works--but if it does offer a little benefit then it was worth it.

9krpmrx8

iTrader: (46)

It's cool, I understand. A DIY on that would be cool, I don't think I have seen one on that.

olddragger

iTrader: (3)

pure water doesnt expand with heat--so where does the coolant system using 100% pure water get its pressure?