Hey Red--I think we are just brainstorming--but you never know what may be discovered.
OD

 

^^^
That's fine with me. I was just curious if I'd missed something where all the sudden this was beginning to look like a necessity.

 

I've never said it was a neccessity or that I am even going to take the time to experiment with it. I hope others don't get the impression that we need this. It is more of a thought as to it's feasibility and if there could ever be any potential benefits to it in some way. I just like thinking of things in a different way sometimes and try to figure out if something has potential or not. I don't care how stupid or different an idea is. I like to give everything a shot at being proven either right or wrong. That's how I learn!

 

I always wondered, what about taking the charge pipe before the IC, and filling a tube around the pipe with ice? Of course the ice would melt, but for a few minutes or like a 20 minute track session would this lower temps? Then after the session, let out a release valve and let out all the water.

Kind of a similar concept to doing like those one shot IC for drag racers, I guess.

Other thing too, is couldn't you re-route some coolant from say a much larger radiator to go around the charge pipes? Again, maybe you'd remove some heat, but with a larger radiator and maybe a small reservoir you'd get some benefits?

 

I was just reading around the web and according to the mustang guys they think 220deg oil is the best temp for hard driving a mustang. They claim thats the Nascar standard for racing. One poster also brings up a point about condinsation but he never got answerd.

Here is the link incase you wanna look it over
http://www.clubcobra.com/forums/showthread.php?p=670116

What temps are people seeing on the Rx8?

 

I'm also wondering why people are worried about it. How are two decently sized oil coolers, mounted directly in the flow of air, not enough? That's more than most cars get. Hell most cars don't even get any external oil coolers. Usually just a coolant line passing through the oil filter housing.

 

I didnt follow the link yet but do they take into consideration the weight of the oil being used in those NASCAR's and that it is probably purpose built oil just for that application and not off the shelf stuff that will be in a street car anytime soon?





youre not really addressing the question which was: would it be benificial to run the coolant and oil at a more closely related temperature? and if so how we we go about doing that?

 

No but the point it the 220deg mark, not what type of oil it is.

 

The type of oil it is plays a huge role. You cant expect an oil that is not engineered to be run at that temperature to be able to handle it and retain is viscos and lubricating properties. If I had to guess, I would say oil that is run in a NASCAR motor is a straight weight and considerably heavier than anything run in a street motor.

 

You can not compare the oil cooling needs of a rotary to a piston engine. A 200 hp rotary engine has greater oil cooling needs than a 1000 hp piston engine!!!

 

Just because a NASCAR team runs something a certain way does not mean it will translate to a street car. We are talking about a completely different application here. Sure we can take a look at what they and other race teams are doing and try to adapt the principals into what we do with our cars. However, there are going to be very few examples of drap and drop, plug and play, pick your favorite computer slogan that will apply from dedicated raceer, espically a NASCAR, to a street rx8.

The type of oil it is plays a huge role. You cant expect an oil that is not engineered to be run at that temperature to be able to handle it and retain is viscos and lubricating properties. If I had to guess, I would say oil that is run in a NASCAR motor is a straight weight and considerably heavier than anything run in a street motor.

 

This is a quote from the Racing Beat Technical Manual so take it as you will and draw your own conclusions:

Oil temperature is critical in rotary engines. Oil temperature entering the engine should never be allowed to exceed 210*F. While many factors affect oil temperature, oil cooler size and location are very important to consider. Roughly one-third of all the engine heat rejected via the water and oil cooling systems goes out through the oil cooler. The oil cooler should get about one-third of the total cooling air flow.

Here's another interesting tidbit that I found in regards to coolant temps:

Under normal driving conditions the water temoerature should not exceed 185*F. Should the temperature reach 200*F fairly slowly, engine damage is not likely. If the rise is fairly rapid due to a broken hose, for example, engine damage is more likely.

Now don't let this make you believe that hitting 200*F temps is going to kill the engine. It's not. This is a good reason why you never drive a cold engine very hard. With Brillo's car and the Mazsport fan mod installed, his coolant temps sat somewhere around 183*F or so for normal driving and only when we were very hard on the car could I get it to exceed 200*F hitting 203*F. I really wish I knew what his oil temps were.

 

For the record, I do believe this forum is a wee bit too paranoid about oil and water temps...

- First of all, the water thermostat isn't 100% open until 203 def F and doesn't start opening until 180 def F. Unless you want to contend that Mazda screwed up specing something as easy as a thermostat, it would seem they like the water temps in the 200 deg area. There are plenty of reasons to keep water temps up including a decrease in emissions and carbon build up in the combustion chamber... and you'll throw a CEL if you don't reach 160 deg F which is the temp required to get out of the cold start open loop control scheme.

...which gets me to another topic for another thread, but why would you invest $200 on electronics to lower your water temps when you can do the same thing with a different $30 thermostat and not wear the fans out... but anyway...

- Most oil systems are designed and most oils are made to run in the 210-220 def F temp range. You want all of the moisture in the water to be continually boiling out because lots of water in lube oil will cause a few additive packages to drop out and you will be stuck with white calcium carbonate sludge everywhere. Any decent quality motor oil will not breakdown at anything under 250 deg.

 

All I was trying to say was, the cobra guys found that 220deg happened to be the opt temp for them to run at and that "also" seems to be nascar standards. For them running colder then 210deg and more then 250deg they would make less HP or so they claim.
Before we get into the "what oil is better" thing shouldn't we first try to find out what the oil heat window is?

So at what point would oil be "to cold" for a rotary, if it is even possable? RB says what it souldn't go over, but do they say anything about what too cold would be?

 

RG-- my oil temps which i monitor constantly, has never --ever--exceeded 240F. And that was on the race track during a red flag condition(sitting still after some laps). That was the only time I have ever seen the coolant temp to actually fall(i activated fans) but the oil temp continued to rise. I run 5W30 Royal purple. It does run cooler than dino.
On the street I have never seen oil temps over 210F-- even with spirited driving. Course I dont do red light--to red light kind of thing. As you know air flow is critical in our car.
For those of you without monitoring capibility (in speaking of driving a cold engine hard) do not think the engine is warm when the stock engine temp gauge is at it's normal "warm" position. The coolant has warmed(around 170F) but the engine's oil is only around 140F. Run it for a couple more miles before "using her"
olddragger

 

The thermostat doesn't need to be open all the way before your coolant temps are optimal. It is there as a regulator. It should always be restricting it somewhat. That's how it controls temperature. When it's fully open, that's when it has lost control and is relying solely on the efficiency of the rest of the cooling system to hopefully keep temps in check.

The fans are what pulls heat away from the radiator. You can run hot coolant through it all day but without the fans, you aren't cooling (when you aren't moving) and depending on your driving conditions you may not have sufficent forward speed for incoming air to cool enough either. Turning the fans on earlier helps pull heat away from the radiator at a lower temperature. Having a lower temperature thermostat may mean more coolant going through the engine sooner but it's only relying on convenction currents to pull the heat away from the radiator until the fans turn on. In the same context but a little more to the extreme, I don't think it would be fair to say not to use any fans since you can just use remove the thermostat. You'll overheat! Go try it, record the results, and tell us how it works! It might make a couple of degree difference but I bet it won't do nearly what the fan mod does. One test result is worth more than a thousand expert opinions though so try it out to verify it.

You have to remember that temperature affects how long the oil will last before it breaks down. Hotter oil temps will break the oil down is less time than lower oil temps will. Heat accelerates the process. Even a high quality oil can break down under 250*F. It just takes longer than at higher temps. Unfortunately our oil systems don't come with timers telling us when our oil is done.

The biggest thing is to try to keep oil and coolant temps as close to each other as possible. Optimally you want your entire engine heating up and cooling down at the same rate. This probably isn't going to happen but getting as close as you can is the goal.

 

OD, where is your oil temperature probe mounted? Is it before the oil enters the engine or after it leaves it?

I personally don't think seeing max oil temps from the track of 240*F is all that big of a deal. You aren't there very long relatively speaking. If you were seeing that in traffic everyday, then I'd be concerned.

 

I use racing beat's adaptors. so it is from a sandwich plate under the oil filter. The coolant temp is from the heater hose( not real happy with that). I do use mechanical gauges. Good ones.
I wasn't worried about that temp of 240F--it was just that it was rising fairly fast and there was no indication of the red flag being lifted--so I shut her down (the lesser of 2 evils I thought). It was just the only time i ever saw the coolant temps fall but the oil temps rise--rose from approx 225 to 240 in about 1 minute. Coolant temp was around 200.
As it stands now I do not have any temp problems. Street temps can be touchy in a hot enviroment. But as luck has it i dont have a lot of traffic to make for a lot of stop and go stuff.
I can definitly see where a hot enviroment and a LOT of stop and go, low speed traffic could possibliy pose a heat problem.
Scotts mod IMO is a good thing. I do wish it was coupled with a 190 thermostat.
JFYI there is a new waterpump coming out soon with better pumping and less cavitation. I think you know who will be offering this.
OD

 

Yup!

 

Our water thermostats are completely closed at 183 deg F and wide open at 203 deg. Yes thermostats regulate - and the RX8's is regulating below 203 and above 180 deg. Turning radiator fans on to try to control water temps to 183 deg F is rediculous since at that temp there is little to no flow even going through the radiator (full flow isn't until coolant temps are 203 deg) - so your cooling something that has next to no flow through it. I fail to see the point of modding your cooling system to try and keep the thermostat closed. Clearly Mazda has no intentions of always wanting coolant temps below 183 deg F or they would have the thermostat opening at 165 degrees and full open by 183 deg. Clearly they are designing for high coolant temps - probably to avoid carbon build-up...

Now don't get me wrong, the lower thermostat isn't going to take care of any problems in stop and go traffic where the thermostat would be wide open but needs to rely on the fan setpoint for cooling. They figured out a setpoint for that and thats what we have... i'm not going to try to second guess them on it since I can only guess at their design conditions.

Also, if you thermostat fails, it fails wide open - and Mazda has a CEL designed for that which gets triggered after driving for a certain amount of time with the engine coolant temp under 160 deg F... and thats exactly whats going to happen unless your on a track beating the bejesus out of the car (i've been there and done that on 2 other cars already). The only way you overheat is when you have an ancient fail closed type of thermostat.


You are still IMO extremely underestimating the durability of motor oil... 210-220 degrees is its design point for continual operation and it will not even think about breaking down till close to 300 deg F for most oils. In the service manual Mazda even states the normal operating pressure at 3000 rpms AND 212 deg F is 58 psi. Thats there design for around the town driving, as i stated you need to be above the boiling point of water for oil life.


Granted there is alot of well deserved temperature concerns based on past roatary engine life - but most things here are a bit overboard.

 

There is always flow through the radiator unless the thermostat is completely closed. When there is little flow, that's because little flow is needed. What coolant is getting to the radiator needs to be cooled down though and that's where the fans come in. If the thermostat was always staying closed, turning the fans on sooner would have no effect on anything. They do though!

I guess Mazda got it right on the 3rd gen RX-7's in regards to cooling too. Those cars would overheat completely stock sitting still in traffic!!! They had all kinds of cooling issues but who are we to question Mazda? The RX-8 has 250, not wait, 247, no wait 238 hp according to Mazda so it must be so!

I'm not underestimating anything. Remember I am a fan of using better, tougher oils and refuse to use crap. Added security is a good thing. You can never have an oil that is too tough and you can never be too careful about trying not to work it any harder than you need to. You shouldn't. I'm not going to drive around all day at 8000 rpm just because my engine has the ability to do it. Maybe I should use cheap crap oil from the grocery store and run around with hotter than neccessary oil temps. I just don't see how this isn't a worse situation. Oil does not need to be above water boiling temperatures for long life!!! They'd go bad in the bottle!

My main concern is keeping oil and coolant temps as close to each other as possible. I don't want a coolant system running at 200*F while the oil system is at 240*F. That is absolutely unacceptable and can create expansion and clearance problems inside the engine. Remember also that oil is what cools the rotors down. The cooler the rotors are, the less likely we are to have hot spots inside the combustion chamber that can lead to detonation. Oil doesn't have to be that hot to do it's job well. It can be at 200*F and perform perfectly.

Are they? We can't learn from the past? How can you go overborad? There is no such thing as overkill. It's always good to have more than you need. I don't understand why so many rotary people feel it is not going overboard to port engines as large as you can, rev them up as high as you can, make them as loud as you can, run as much boost as you can while using bandaids of ecu's and get rid of every creature comfort, and still have them as perfectly streetable and yet there is still someone out there that thinks you can go too far on a cooling system? Wow!

 

oh i see... a little cooling = good so massive amounts of cooling must = outstanding... Too bad that logic does not stand up in the real world too well as about 99% of the time as there is always a trade-off.


The thermostat IS CLOSED at 180 deg F by spec of the thermostat - the radiator is blocked off at that point. There are no "if", "ands", or "buts" about it. To mod your engine to keep the thermostat shut or nearly completely shut defeats the whole design of the cooling scheme - which is related to the oil cooling scheme, and is related to the engine control scheme and engine life. You can not adress 1 part of the equation and be completely blind about the other aspects. Try running an engine for a few years with the thermostat hung wide open and always have excessive cooling and see what happens - its not pretty...

Because an older RX7 design with twin-turbos had problems we should for ever be overly paranoid? Umm... no

Engine oil would go bad in a bottle at the store if not kept to the boiling point? Do you understand thats why oil now comes in a sealed bottle? You would be shocked how much water accumulates in a barrel of oil left outside in a closed drum - I've been there and had lab results screwed up by that. 212 degrees is the generally accepted operating point and that is why there are 2 service schedules in your owners manual - 1 that deals with short trips frequently where the oil does not get up to temp (leading to water accumulation) and 1 that deals with extended trips and normal oil operating temps. I find it completely fascinating you can start a 50 page thread on motor oils, yet not even understand the basic theory of how they are intended to operate. I helped design/commission an oil coking testing rig in the past, you would be shocked at how high of temperatures you need to maintain for the experiment to yiled results... 250 deg F is nothing... 300 isn't even anything to get excited about

 

Were you not testing high temp oils in the coking? Oils that can go to 600-700 degrees? Don't think our engine can go there! Much less our seals! Trucks maybe but not passenger cars?
Oil temps of 212F is not the generally accepted operating point for our rotary. Matter of fact Mazda said that the oil pressure should be 50.8(not 58) at 3K with the 5W/20 (only weight mazda instructed us to use) oil at 212F. The engine will not do that. At 185F at 3 K with 5W20 we are running at 48-49. With 5W/30 same parameters we run about 52. I dont know what it would be at 212--haven't looked.
Most car people will tell you 250F max for dino oil--at that point the oil begins to not be able to do the job it is supposed too. Who wants to change oil everytime you run it a little hard? Rotory owners need a little cushion as this engine builds heat fast.
Now I will give it back to the experts here--as I am not.
olddragger
dont know why i cant shut up

 

I was never trying to start a which oil is better debate, I was trying to speak in generalities. I never did get a change to follow that link you posted as its been a rough couple days. I took waht you posted to mean the mustang guys were taking "optimal" temps straight out of nascar application and applying it their street cars. I was mostly disregarding what the number was and saying that taking from a race application and adding it straight to a street car "as is" is probably not the greatest idea. I didn't realize they were saying that the temp was what they found to work best for them and that it just happened to be the same as wht NASCAR thinks. So now we are on the same page, my appologies.

 

Well apparently the oil/air question just popped up on the RX-7 forum with a link to the Laminova heat exchangers. Someone brought up that ISC Racing has an upgraded cooling system for the 2nd generation RX-7 that uses an oil/ water system. They even have a picture of it. Interesting as these guys are primarily concerned with racing. Scroll down about a 3rd of the way on the left.

http://www.iscracing.net/2nd_Gen_Parts.htm