olddragger

iTrader: (3)

Ok, I am just throwing this out guys, but wondering why the engine coolant passages/system are designed to flow the way they are?
The coolant enters and exits at the front of the engine---right? Why?
Couldn't the renesis have the coolant exit in the rear of the engine?
That would eliminate the return flow of hot coolant through the engine, help with the rear rotor running hotter than the front, open more passageways for cool coolant and I think allow for better all over cooling?
To visualize--a lot of people (and myself for a period of time) have temp gauges hooked up to the RB adapter that uses the heater hose. The sensor is monitoring the temps of the coolant in that hose. That heater hose is supplied by a pipe that exits the rear of the engine on the drivers side. The temps of that coolant that is supplied by the rear of the engine is what is seen. Its pretty hot--right?
Ok, then the coolant has to turn and make its way back to the radiator. Why? Its already hot? Why circulate it back to the front of the engine? Why not let it exit to the radiator from that point?
Anyone?
Team---yes I have searched everywhere
OD

9krpmrx8

iTrader: (46)

Does anyone have a diagram of the Renesis coolant flow path? Maybe a visualization would help to see why they did this.

usnidc

Here is my guess:

"cold" water enters at the front and picks up heat as it travels through the engine. so the water at the front of the engine is removing more heat that at the back. By passing back through, the coolant is actually redistributing some of the heat back to the front of the engine thus making the temp more equal front to back. if it exited from the back, the front housing would be running even cooler than the back housing.

I may be wrong though...

Brettus

iTrader: (2)

Or it could just be that that was the easiest way to do it . Also you should look at where the cooler water passes over - It would make sense to pass over the intake/compression part of the housings first - yes ?

InnerDragon103

My educated guess would be for spacing reasons... The radiator of a car is just like a heat exchanger, of which i've seen two styles; one style has cooling fluid running from one end to the other of the exchanger, and the other style has a U shape (and yes, the outlet temp is much warmer than the inlet temp). Perhaps the design of the engine or complexity of routing the coolant channels in the engine may have had something to do with it? I'll try to see if i can find something on it. Although 'hot' coolant may be passing by the engine again, it is still removing heat from the engine, to a lesser degree of course, as opposed to 'cool' coolant.

WindtalkerCS

I think you would be surprised to find that the temp of the water heading in isn't too much cooler then the temp heading out.

InnerDragon103

I found this @ wikipedia:

Unlike a piston engine, where the cylinder is cooled by the incoming charge after being heated by combustion, Wankel rotor housings are constantly heated on one side and cooled on the other, leading to high local temperatures and unequal thermal expansion. While this places high demands on the materials used, the simplicity of the Wankel makes it easier to use alternative materials like exotic alloys and ceramics. With water cooling in a radial or axial flow direction, with the hot water from the hot bow heating the cold bow, the thermal expansion remains tolerable.

Still doesnt explain why though.

nycgps

iTrader: (1)

space is one thing

but most important thing is that it travels thru hot areas first --- then back to "not so hot areas, to make the temperature more "even" across the whole engine.

ken-x8

I think in/out at the same end is a tradition from conventional front longitudinal engine layout. The water pump is at the front because the fan is on it and the radiator is in the front. Return is in the front because it's a shorter path. Return from the back would need longer hoses.

I think you're on to something. One thing that killed straight 8s (remember those?) is that the rear cylinders never got enough cooling. Do rear rotors in RX's have a cooling problem?

With modern transverse engines, coolant return could be from the opposite end, without the plumbing being any longer.

Ken

olddragger

iTrader: (3)

The rear rotor is known to run hotter than the front.
I do now some v/8 guys that do reverse cooling.
I remember the old Packard straight 8's ---damn what an engine!
What got me thinking about this was since temps are critical to our engines in what way can the engine be better cooled. Yes, I started the secondary radiator thing for our car and that works very well to keep the overall temps in check, but since the water temp is only checked at one spot, what is happening elsewhere?
Yes I know builders waffle coolant channels, use different coolants to help with localized hot spots, increase coolant pressure/velocity etc etc in dealing with heat issues, but in thinking out of the box, this idea came to mind.
There are two coolant lines that exit the rear of the engine, one for the heater and the other is the Throttle body line. The temps of the coolant that come out of the engine are equal to (within 10 degrees) of the coolant that is in the hose going to the radiator.
This to me means that the coolant that comes back to the front of the engine is not cooling anything very much.

olddragger

iTrader: (3)

ok in further thinking, its my understanding that the "weak" spots in our engine is the corner of the apex seal and the side seal spring. These are the weak spots again from what I understand, because of the heat from the side exhaust port that these areas have to deal with.
Now if that is a critical area then why doesnt the engine have cooler coolant flowing through those spots? If I am not wrong that area is one in which the returning coolant is used?
Two "Hot" areas in this engine
1- combustion side
2- exhaust port.
Combustion side uses coolant from the radiator
exhaust side uses coolant that has already passed through other hot areas?
Poor design? Can we change that?
OD

nycgps

iTrader: (1)

Mazda has been using this "design"(flow path) for the past 40+ years. spark plug is the hottest spot on the engine. coolest of course is the intake area.

most of the heat will be carried away via exhaust gas this is why the exhaust side don't need as much cooling as the spark plug side.

there is nothing much we can do to change the coolant flow path.

olddragger

iTrader: (3)

disagree that the exhaust ports are cooled enough. The coolant flow has been in use for all those years BUT this is the 1st side port exhaust engine. Before, the exhaust ports were not as heat soaked as they are now. We also have higher EGT's than the previous models.
All in all, it a spot that could be improved. I think?
OD

HiFlite999

iTrader: (2)

Back to basics for a moment. While the rate of heat transfer for radiative cooling goes as the fourth power of the temperature difference, that rate only varies directly with temperture difference in the case of contact cooling (Fourier's Equation). At the junction of the hot metal to the coolant, the temperature difference isn't that much when one considers that such things are measured relative to abosolute zero. In steady-state motoring, say the metal on the cooling passage surface is at 250F and water at 200F. In degrees Kelvin this is 394 K vs 366 K, or a difference of 7.2%. 180F water would give 255 K or 9.9%. 180F water cools about 30% more efficiently than 200F water in this example.

However, if one looks at the passage of water through the engine from the standpoint of design, the total heat transfer in different areas of the engine can be adjusted by adjusting the flow made available to different passageways as well as the area of surfaces in contact with the water. The loss in cooling efficiency of the water as its temperature rises, can be compensated for by manipulating the contact area, flow and flow velocity. If one knows in advance what the desired steady-state temperture gradient is, one can achieve the desired cooling.

However, it seem to me, again from Fourier's Equation, one can play another game. The rate of heat transfer for the example above with a 250F surface and 180F water is exactly the same as for a 270F surface and 200F water! The rate varies only with the temperature difference. In that way, it makes some sense to cool the colder surfaces with cool water, and hotter surfaces with hot water.

If one looks at a side view of a rotor housing, it's pretty clear the engineers were playing extensively with cooling passages to get the desired effects. (see attached). It's reasonable to assume they also included the effects of temperature rise as the coolant passes through the engine in their goal of achieving the right thermal balances. Because of the azimuthal variations around the housing in a rotary, this must have been both vastly more difficult to do than with a chevy V-8, and particularly so in light of the computational power available at the time (about zero).

Very interesting question OD! After an hour's thought while eating my can of beans for lunch, my comments would be:
1) Since the design of the 13b predated modern computers, it's likely there's room for considerable improvement.
2) Without a thorough analysis way beyond a amateur's means, I'd be extremely reluctant to make cooling mods internal to the 13b short block.

zoom44

you have a reason to believe they didnt do any design computations using "modern" computers for the coolant flow through the Renesis? this was in 2000-2003 remember.

Hell there are/were videos and pictures around showing the process of designing just the proper angle and placement for the rear door inner handle. They made that little japanese woman open the rear door THOUSANDS of times and used computer modeling for various other size and shape people so the door would open not to hard and not to easy ( too easy can actually flip you out of the car!) but JUST RIGHT.

HiFlite999

iTrader: (2)

Sorry, I wasn't clear on that. While the Renny is from 2000, the 13b is from 1980ish and before. They weren't starting from a clean sheet of paper in 2000 and may have inherited things from the original design that weren't updatable: only speculation on my part, though supported by some conventional wisdom that the rear rotor gets too hot. It doesn't change my basic take on the matter which is blind modding of the internal cooling system is probably a bad idea. YMMV.

zoom44

meh no worries HiFLite. I feel like i over reacted to your post

Rote8

We need to find out where to drill and tap coolant passages on the rear end plate!

What about the heater hose on the drivers side rear, is that an "in" or an "out"?

It might be interesting to put temp sensors all over the block and then add (or subtract?) flow to the rear heater/block hose connector.

MazdaManiac

iTrader: (3)

You can't really cool them any more. They are way too hot to be given more direct access to the coolant. Their heat is allowed to precess through the motor to the adjoining coolant jackets.

But NOT because of coolant flow.

EricMeyer

I never knew these engines had water cooling problems. In race trim and operation our weak link is side seal spring life. Everything else is peachy.

HiFlite999

iTrader: (2)

Good! While you're here, have you ever experienced water hoses collapsing at high rpm?

jasonrxeight

ok theres a diagram showing how the water is flown.
I think they tried to is to keep the intake and compress area as cold as possible, the expansion and exhaust area as hot as possible.
cold intake and compress area reduces pinging, hot expansion and exhaust area reduced thermal leak.
its the same with piston engines too. cold water always goes in from the bottom, and hot going out from the top in order to reduce pinging and thermal leak.

DocBeech

iTrader: (1)

Guys I understand yall are putting a lot of emphasis on water flow and direction, but also remember that different metals are better at dispersing heat than others. Take aluminum for instance. It is a great conductor of heat, copper is a little better, but well I don't see us with copper engines anytime soon. Don't forget how well the block is at spreading that heat out. Also you can affect cooling by using better coolants than say prestone 50/50. The use of Water Wetter with less anti freeze allows for better flow of the coolant. Having the coolant set at the right temp so its not to thick, and allowing for better air flow. I installed a vented carbon fiber hood, and there has been a noticable drop in engine temp. They make other things like brake cooling units, and transmission cooling units. Cooling the transmission would help by pulling some of that heat away from the block, and not allowing the transmission to assist in the heating.

One of the biggest things that can be done though, and that I am currently looking into is a radiator sprayer. Every time I went to the track with my dad, and we were pushing cars extremely hard over long ours we carried sprayers with ice water in them. We would spray the engines and radiators and you could watch the temp drop on the gauges. Then one day we installed an intercooler sprayer with a nos bottle and just ever so lightly gave the radiator a spray once in a while, and it helped incredibly with cooling.

MazdaManiac

iTrader: (3)

And this is one of the fundamental problems with this motor - it is a sandwich of dissimilar metals, each with their own thermal properties. When things get really hot, bad stuff happens.

Uh, no. That is just nonsense.

How are you quantifying that?

How, exactly, would you install a transmission cooler on a 6-speed?

Horrible, horrible idea.
First of all, if I were the track marshal, I'd punt you for polluting the track with water.
More importantly, spearing cold water on a hot radiator is just begging for massive thermal fatigue.

DocBeech

iTrader: (1)

I can see where having two different metals bolted up causes a problem with heating and cooling. They would expand and contract at different rates.

On the second note I meant better collant flow not air. Bad habit to be typing and charting at the same time at work.

I can quantify the cooler temps on the engine pretty easily by watching the temp gauge.

I understand there isn't as much of a need on cooling a manual transmission than an automatic. Ive seen plenty of Baja Trucks when I was stationed in SoCal that have a cooling system in place on the manual transmission so I know it can be done on ours too.

Intercooler sprayers are not new, and I have never had a track marshal complain, or anyone else for that matter. Usually your not spraying ice water on the track, while your moving. Thats what the nos tank with intercooler sprayer is for. It works really well though, and again never had a problem with a radiator, intercooler, or the inspectors with a spray system.