ken-x8

Pure water expands. Coefficient of expansion is maybe 10% greater than that of mercury. But it's the vapor pressure that the radiator cap balances.

What's the "flex a lite vsc" you mentioned in your prior post? A fan controller you added?

Ken

PhillipM

Not really, that flow is also travelling faster through the engine and taking less heat per unit/time, the water pretty much acts as a solid thermal conductor (unless it's boiling, or cavitating), the faster it can flow heat to the radiator, the larger the delta T at the radiator to the airflow and the more efficient the radiator becomes. The radiator doesn't really care how fast the water is flowing through it (alright, there's the boundary effects for the heat transfer from the water to the rad, but that could go either way depending on the internal structure), it just shifts heat to the air, the bigger the temperature difference between the rad and the air, the better it is at doing that.
The only time higher GPM will hurt the cooling, is if it starts to remove the nucleate boiling set up in specific regions, as the flow would probably not be turbulant enough to offer the same heat transfer efficiency in the hot spots.

The reason cars don't go for massive GPM of flow is obviously because the returns are rapidly diminishing whilst at the same time the power absorbed by the water pump is exponentially increasing*, there rapidly comes a point where marginal increases result in massive downsides, and you're better off concentrating on improving the radiator or heat transfer in the cooling passages - especially on a road going vehicle with fuel economy a big factor and thermostats needed for 90% of the time anyway.
I can see where you are trying to come from - the RX8's issue is the radiator, not the other parts of the system, but faster flow would still improve the efficiency of the standard radiator - that doesn't necessarily mean it'd be cost effective or worthwhile though, like I said, water flow speed has those diminishing returns...


*You can actually get to the point where the pump absorbs so much power that the car runs hotter in 'normal' conditions because you have to generate so much more engine power to turn the bloody pump...

PhillipM

As ken says, it does indeed increase with heat, and by a fair amount too, but as the temperature increases so does the amount of water vapour released, which also generates the increased pressure in a sealed system.

Easy_E1

iTrader: (2)

I know what your saying PhillipM. And I agree.
It's all in radiator surface and coolant flow. The rate of heat flow depends on the fluid properties, flow rate, conductance to the surface, and the surface area of the radiator.
It's a fine line between flow, radiator surface area (for air flow and coolant flow) and GPM through the radiator and the engine to displace heat efficiently. Lets not forget ambient temps as well.
The differential between ambient temps and coolant temps also bring into the equation the capabilities of the radiator to displace the heat. Higher ambient temperature and less efficient the radiator becomes.
One of the issues we have here in AZ. Our pavement surface can become 170+ degrees. Ambient temps in the 120+ range. An inadequate cooling system will show it's true colors real quick in this environment.

The bottom line is Mazda failed on the cooling system in the RX8 for extreme conditions.

PhillipM

It takes a hell of a radiator and oil cooler to keep the Renny cool under full throttle, (and to stop the EGT's slowly creeping up too) it's took us a few iterations to get there in the buggy.

ASH8

Always has in Rotaries...never really been any different, every rotary ever made has "suffered" in extreme conditions...nothing new really.

As we know Mazda like all makers changed many years ago to thin/light alloy Radiators and plastic tanks.

I always thought the "wider profile width" Radiators used in the RX-2,3,4,5 and early 7's were better.

But again if your Cooling System was less than perfect or not maintained, any rotary will show it up and not like it...like wrong Pressure Cap, blocked air flow, wrong positioning.

I don't agree that Mazda have necessarily got it wrong, as I said they make their cars for all world markets/climates, what is/was wrong is clearly evident by the changes done in S2 upgrade...just like the FD upgrades.

IMO it is air flow through the radiator as the #1 issue, fan motors are crapping out/slowing, also fan speed is not high enough with AC on in S1, especially in stop go traffic.

PhillipM

Thinner but wider radiators are more efficent in terms of cooling vs space, which is why cars have trended towards thinner rads, but they're making them long and wider instead, it has packaging benefits elsewhere.

Problem with the '8 is the small nose means both the length and height are limited too.

Highway8

iTrader: (11)

I think you should concentrate your attention on the oil coolers.

We all know that the water and oil temps are related and if you have ever watched the oil temp and water temp guages during heavy acceleration you will see that the oil temps climb faster and higher then the water temps. Additionaly, during stop and go driving in hot climates, the oil temps will be much higher then water temps because there is no air flow.

If you have ever gotten your car to overheat, have you noticed the oil temps? Probably 260+, and I would bet nobody has ever overheated a car with oil temps below 250.

Solution, if your problem is stop and go traffic, install a fan on one of the oil coolers.

If your problem is during high load driving, upgrade the oil coolers.

You could start with changing the lines to something like what Racing Beat offers. They claim less restriction and higher pressures, but I think the real key is in the stock oil thermostat restriction, so I would remove the drivers side cooler and install a larger and more effecient oil cooler along with a real oil thermostat. Best to install new oil cooler lines at the same time.

This is not the easiest or cheapest modification, however if you shop around for a used racing oil cooler and you dont get super expensive lines/fittings, you can do a great upgrade for a few hundred dollars and a fun saturday getting oilly.

PhillipM

How much are you betting on that one?

Highway8

iTrader: (11)

Let me rephrase. With a properly functioning water cooling system, I bet nobody has overheated with oil temps below 250. If they have, I would be shocked.

Let me explain why I believe this to be true.

I have a big intercooler in front of my radiator, immediately after installing that intercooler my water temps became a problem but oil temps were fine. Doesnt count because the water cooling system was compromised due to the intercooler. To conteract the reduction of water cooling I installed a secondary radiator into the right side oil cooler location and removed both oil coolers and lines and installed 1 larger oil cooler on the drivers side. Water temps were now much better but oil temps began to rise. While on the track oil temps quickly got hot 250-260 but water temps were fine until oil temps reached 265+ then water temps went from 210-215 up to 220, 225, 230 and as high as 240.

Good water cooling, bad oil cooling and I overheat. So it is my belief that the cooling system is fine until the oil temps get above 250-260 and which point the water temps are compromised by the oil temps.

If you dont mind burning a large amoutn of fuel, you can sit in your driveway and do the same thing by reving the motor to 3K RPM and watch the oil temps climb and climb. The ECT will stay low for a while but eventualy because of no air flow across the oil coolers, the oil temp will drag the ECT's up with it.

Listening to Eric Meyer, they over cool there engine oil (keep below 210 I believe) with a very larger oil cooler and are able to block off a large portion of the radiator.

PhillipM

Yep, I use a massive oil cooler too - in fact, it was originally a big hydraulic oil cooling unit off an excavator - but you can still get the water too hot if the system is compromised there, just as you can still get oil too hot even with a massive water cooling system.

olddragger

iTrader: (3)

the water and oil do work together. Just stands to reason. I believe most peoples delta temps are about 15-20F with unmodified systems?
I have found by addressing coolant temps--the oil temps will follow if everything is working ok.
I have had one builder tell me to not get the oil temps over 210F--I asked him "How?" He laughed.
I have experienced that the oil will react to lower coolant temps better than the coolant reacting to lower oil temps.

Lots of good points in here.

I am doing this thermostat change to try to increase the coolant flow rate during low speed driving. With residual heat in the engine from driving on the interstate, i have noticed temperature spikes after stopping at a red light and then increasing rpms to restart. Temps will rise rapidly from 175F to 190F as i blip the throttle from idle to 3.5K ( fans/airflow is a constant during this). The temperature will increase in concert with my increasing the rpms. Stop when I let it idle, increase sharply when i increase the rpms suddenly.
If I repeat the scenario and hold the throttle steady after stopping at 2.5K the temperature will only slowly rise at a very slow and steady rate. I think that is a pretty good sign that the coolant flow at idle could be better? Maybe this is what is happening during stop and go driving in hot weather?
I dont really know--but I guess it does bear thinking about?
OD

dannobre

iTrader: (3)

-All you have to do is ground the relay triggers with a switch...and they will stay on till you shut off the switch.

Hell you can jump them with a bit of wire if you need to . Had to do that at the track on Nemesis8's car once

olddragger

iTrader: (3)

true that.

Flashwing

The problem is this behavior is all irrelevant in respect to the thermostat. The thermostat's job is to maintain equilibrium provided there is excess cooling capability within the system. Once the available cooling capability (let's call it efficiency) has been saturated, the thermostat is 100% open and now no longer part of the equation. The only way you bring cooling efficiency back into the system is by incorporating additional airflow via fans or vehicle movement or by increasing available cooling surface area such as larger or additional radiators.

Whether or not coolant flow needs to be increased is another issue. The thermostat is the incorrect place to attack this problem because after 180 degrees it no longer matters. You might as well crack the engine open and take it out because it would have the same effect. The thermostat's job is no different than the PCM's fuel trim capability. It is all designed to deal with environmental changes and inconsistencies. Fuel trims don't matter in open loop and thermostat size or flow doesn't matter when it reaches 181 degrees.

Easy_E1

iTrader: (2)

Glad we all have that figured out now.


This tells me that the radiator has reached the point of being unable to remove the heat from the coolant due to a lack of radiator surface area and air flow.
The easiest solution is an increase in radiator cooling surface and an increase in air flow capabilities. I don't know the CFM of the Mazda fans. But lets say you need to move as much air (CFM) as the equivalency of driving say 50 mph. To maybe keep the car at normal operating temps. That's a lot of air. Even that might not be enough under high engine load conditions. Such as on a race track in high ambient temperatures. Ok. It isn't enough.

So, before you turbocharge your radiator fans,,,,
Increase the cooling capabilities by incorporating more cooling surface that can be affected by air flow. And displace the heat into the atmosphere where it can increase global warming.

olddragger

iTrader: (3)

good points. I do agree that the cooling system can be managed in different ways. Increasing air flow or face front of the radiator are two good ones. But, I do beleive that increasing low rpm flow is something that can also be done. Look at what the rock crawlers guys have to do. I mean they do all the ones mentioned but they also try to increase coolant flow during the low rpms they use. They even have a custom designed impeller on their water pumps to do this. They also use this type thermostat, at least the ones I have spoken too.

The thermostat is a restricter to flow. It has to be. The balance thermostat ( barrel type) is also a restrictor. Just not as much when fully open. It is also less prone to fight the water flow during opening. Less restriction generally means increased flow.
I need to post a picture of the top part of each thermostat in the housing. Then it will be easy to see how much less of a restrictor this type of thermostat is.

OD
The temp spikes i am seeing are directly related to coolant flow. Thats why increasing the rpm, and speeding up the water pump flow reveals it.

1.3_LittersOfFurry

iTrader: (4)

How big of a temp spike are you talking about?

olddragger

iTrader: (3)

https://www.rx8club.com/attachment.p...1&d=1317335846

here is a picture that shows how bigger the opening is on the barrel type.

olddragger

iTrader: (3)

temperatures have fallen in Ga to the high 40's in the morning. I can say with confidence that warm up was extended by 1 min or so with this thermostat change. What has noticibly changed is the behavior after 170F. I like it.
It is amazing at the heat that is generated under load and higher rpm's