salituro64

I keep reading about that rotary engines run hot. Does anyone know what the normal operating temparature for an RX8? Unfortunately you can't tell by the tmeperature gauge that has no numbers.

mysql101

if you have a canscan, you can plug it in and see what your car gauges are reading. I think i was reading 1600 - 1700 degrees at my cat sensor.

truemagellen

9000Rpms you do the math :D

G8rboy

Looking at the shop manual, the thermostat fully opens at ~200F, and oil pressure is repeatedly defined as being measured at 212F... so I would guesstimate the normal operating temp is between 200F and 220F.

The exhaust/cat temps that Jason mentioned above are definitely hotter than normal (piston) engine cars. Normal warmed-up cat temps at idle are supposed to be around 1000F, and I've see the 1700F+ readings with my canscan during hard runs.

truemagellen

at those temperatures you can do hard soldering (gold, silver, platinum, copper, brass...but it is silver soldering)...pretty insane if you think about it

rotarygod

212 for oil temperature is dangerously high for a rotary. Under no circumstances have you ever wanted oil temps over 200 degrees F. I can't believe that this would be different for the Renesis. Optimally you don't want the coolant over this either.

salituro64

So at 200 degrees, the rotarty engine (not the CAT) itself does not run much hotter compared to a normal piston egine. Don't normal piston engines run at around 190?

G8rboy

Good to know. Since the t-stat fully opens at 203F (just looked it up again), and we have such a massive radiator, I suppose the coolant and oil temps could/should remain near that point. It also makes me wonder about how thin the 5W20 oil is at that temp... I used to run 15W50 synth in my Miata because of the heat in Florida and constant high revving.

dragula53

I am not a rotarygod or anything, but I thought that the rotary engine does run hot, which is the reason for having oil coolers.
It might not operate hot because of it's radiators and oil coolers, but they are the cure for the symptoms.
Feel free to correct me if I am wrong, as that is only a conclusion I drew from thinking about it. I have no idea about the safe operating oil temperature or anything like that. And the above hypothesis probably has nothing to do with the original question. I'm just musing aloud.

I know twin turbo rx-7's ran extremely hot because of turbochargers and catalytic converter proximity required for meeting emissions, and was one of their serious shortfalls, and that the automatic transmission model only had one oil cooler, which further exacerbated the problem. (well, that and plastic radiators, and a vacuum hose spaghetti mess with a short lifespan due to excessive engine bay heat). Ya all should be grateful the rx-8 didn't inherit the rx-7 laundry list of problems .

valpac

iTrader: (2)

Oil in a piston engine does pretty much single duty, lubrication. In a rotary, the oil does double duty, lubrication AND cooling. Since water has no way to reach the rotars, they are cooled as oils is sprayed thru venturi ports in the eccentric shaft. Engine oil retains heat more than coolant and therfore not as efficient at cooling the engine. Oil temps increase which make oil coolers necessary.

The effect of having two extremely hot rotors cooled only by engine oil causes heat soaking of the housings and endplates. As coolant runs thru the housings and endplates it must remove the "excess" heat in the heat soaked engine parts. Water temps increase as well which make a larger radiator necessary.

Also, remember Work = Heat. Noone can argue that the rotors aren't working their little hearts out for us!

So the moral to the story. Make sure you have adequate oil levels and that you change the oil OFTEN. Oil is atomized thru venturi ports so they are very, very small. Clog them with dirt and you WILL be replacing the engine.

dragula53

that's very interesting, thank you.

I was under the impression that combustion chamber shape was what caused heat soak. Something along the lines of more surface area for heat to be absorbed. And then the oil running through an already heat soaked engine gets hot, so needs to be cooled. Oil gets injected into the side housings and other places, because it has to lubricate, and is just the way it is for a rotary to be lubricated. I'm not really certain I am correct, but this is the way I understood it. I welcome the opportunity to be educated, so anybody can feel free to refute any of the above statements.

valpac

iTrader: (2)

yw, dragula.

yes, the heat soak comes from "uncooled" rotars flying aroung the rotar housing. The oil is sprayed inside the hollow rotors (opposite of combustion surfaces) just to keep them from melt down. They pretty much stay very hot all the time. No way around that really.

I asked a friend (raced RX-7's SCCA) why can't coolant be injected into the rotors instead of oil. He said the only way water is effective is in large volumes. You can't have large quantities of water sloshing around inside the rotors (balance would be all messed up). Plus water would steam, seep past the side and corners seals right into the combustion chambers. Not good. If oil gets around the side seals into the combustion chamber, no big deal as it's there already. That explains why more oil is consumed when the car is driven hard. Oil is mixed with gas via the sump (continuously and varies w/ RPM's) and some "thin" oil bypasses the seals as well. Another reason to have "fresh" oil in the engine.

Oil is SO important to the health and longevity of the rotary engine. If I could afford it, I'd replace it every 1000 miles. I'm on a less than 3000 mile schedule anyway, so I'm not gonna sweat it too much.

dragula53

Thanks a lot, that rocks.

appreciate the info.

that explains a bunch.

salituro64

Based on all this information, thanks a lot, I am going to stay with dino oil rather than risk synthetic. Oil seems to be a siignificant part of the equation in the proper function of the rotary. Thanks again for eveyone's input. Very informative.

valpac

iTrader: (2)

a little off topic but,

http://www.monito.com/wankel/rce.html

Aoshi Shinomori

That probably has something to do with it, but I think it also has a lot to do with the design of the engine. The S2000 also had the 9000 redline, but I don't think it got quite as hot as the Renesis does.

Go48

Hey valpac, this statement prompts me to write with a request. Are you able to elaborate a bit on how oil moves from the sump through the engine and back to the sump? My oil has a faint strange smell that smacks of gas, which I gather is not too unusual, but I would just like to better understand how the gas gets into the oil in a rotary engine.

I understand the phenomena that causes this in piston engines--I think--but the rotary is obviously a much different animal as far as cooling/lubrication goes.

Thanks!

valpac

iTrader: (2)

Oil goes from the sump or metering pump and mixed with air and fuel and consumed in the combustion chamber. Its a continous one way flow of oil from pan to combustion, not returned.

The gas smell is likely coming from seepage past the various seals. On the side of the rotor there are side seals (sealing combustion/exhaust), corner seals (round seals that make the side seals continuous along the perimeter of the rotor), and oil o-ring and oil scraper. The scraper kinda acts like an oil squeegee on the side housing. As I said before, oil is in this area to cool the rotor and lubricates the eccentric bearing. This oil recycles through the engine.

If oil gets by the scraper and o-ring (inevitable) and gas gets by the side/corner seals (also inevitable) than the oil is gonna get contaminated with gas , hence the smell.

Oil and gas are always in very close proximity with each other. Look at the attached picture, the distance between the scraper and side seal midway between the apexes is small. Some mixing is going to occur. Its normal.

RotorManiac

valpac:
your information is absolutely amazing and valuable. Thanks.

Please bare with me, I'd like to ask you something that made me wonder the last few days:
I known racer here in my country has an RX8 for a couple of months now, he has modded the hell out of it, and when he gave me a ride (although the car has only 15000km) I found out it is VERY fast, compared to stock.
We talked for a while, he said that all the car's fluids are changed, because he pushes it to the limit all the time. What caught my attention, is that he uses RACING OIL, full synthentic. To be more specific MOTUL racing oil 5w-30. He also said he keeps changing it every 2000km (its pricy, but he can afford it).
What do you think about the 'full synthetic' part, the brand and the freuqency he's changing it?
Furthermore, an aftermarket radiator (like the MS one), will it help the rotary engine with the heat problems?

Thanks

p.s. Sorry if this post is irrelevant to the topic. If thread starter wants me to delete it, I will.

Go48

Thanks valpac, that helps me understand the process. Still learning about the rotary.

Razpewton

One of the warnings I did receive from a rotary mechanic I know, was if you've been running your car on a hot day for an extended period of time, do NOT park it on the grass. It will set you lawn on fire. In fact, there was a thread in here a while back of someone who parked theirs in their garage over arag, and it caught fire, causing considerable smoke damage.

valpac

iTrader: (2)

I have never used synthetic in either my old RX-7 or Rx-8. Maybe the fact that he's racing it has some bearing as to why he uses synth. I've never had problems using reg. oil. (probable because I change it so often) I see no real value added in synths. IMO. Any good SL grade oil works for me.

Frequency of oil changes is more important than type of oil used. Change it as often as you can afford, EVERY 3000 miles, religiously. Or less.

valpac

iTrader: (2)

As an aside. When rotary engines were first introduced in this country, they got a real bad rap. And here's why.

Most people were used to piston engines. They don't use oil by design and new engines usually never burn oil. So new Rotary car owners were either never told that rotaries use oil or didnt believe it if they were told. Consequently, they just drove 'em. And what happens is catastrophic.

When oil is gone, the rotors over heat. Since the rotor housing is aluminum and the side housings are cast iron, they behave differently when heated to the extreme. The rotor housing would warp, water would get past the O-rings and contact the scalding rotor, cracking them. Water now mixes with oil (very bad). If the car runs at all, it runs very badly until all the water exits the car in the form of white smoke (mosquito truck effect).

Check your oil often.

rotarygod

That warning is actually posted in the RX-7 owners manual! Check the RX-8 manual to see if it is still there.

wakeech

doesn't sound right to me: water cools better than oil, and can take higher tempuratures for what it needs to do (just carry heat). the main problem is that you actually can't get water in there without plumbing the coolant system into the e-shaft. the primary reason there's oil in the e-shaft is so it can feed its own bearings (being that it spins in the middle of the block, and can't slosh through the sump), then secondarily they thought it was a good idea to throw some into the rotors while they were at it (why not, right?). also, how on earth would you plumb the water back out again when the oil has to sump out from the rotor journal (which needs lube whether you're spitting it into the rotor or not)?

anyways, whatever the case, you can't do it.

with modern detergants, dirt contamination isn't such a deal as it used to be with the molecules suspended so don't everyone start freaking out and changing at intervals smaller than the manufacturer's recommended (which are already as close as they think the maintence service market will bear).