PhillipM

No, the bearings/rotors is where it's hottest, it'll cool down a little when it gets to the pan, but not much.

onefatsurfer

so then an increased capacity oil pan + water injection onto the oil coolers, + oil pan heater + 50 weight oil + filter magnets + premix = no more problems? Seems to me like these would all help with the problem.

Maybe just a higher displacement oil pump would do?

(edit: BTW, I'm becoming more and more a believer in the filter magnet thing. ordered some and will be popping them on there @ my next oil change (hopefully early next week)

9krpmrx8

iTrader: (46)

I will have to look for a bung to have welded for the oil temp sending unit.

Flashwing

The problem is that you're assuming the cooling capability of the oil system remains static through the whole process which we know isn't true. Oil cooler capability is influenced by driving speed so you could easily see 250 degrees in the pan but lose much more heat than that before the oil enters the motor.

You could, in theory, see static temperatures in the pan but have variations as the oil enters the motor. Would you suggest tapping coolant temperatures at the thermostat or inside the radiator?

Arguing about temperature is a dead end. The majority of RX8 owners have no idea what their oil temperatures are. If you want to increase your cooling capacity simply open up the space behind the coolers. I'm missing my passenger side mud guard at the moment and I have problems with oil even getting up to temperature.

No no no. Increasing the pan size is not the answer and will only result in you shelling out big bucks for your oil change. Adding 3 or 5 quarts to the oil system will only delay the inevitable. Plus, with more oil in the system it will take a much longer time to cool due to oil not shedding heat as easily as water. That and the fact that it will take a seriously long time for your oil to come up to temperature.

The GReddy oil pan increased your oil capacity because they designed it to work with their turbo system. Since you have now added another oil using device to the mix they balanced out the capacity to compensate.

Aside from the OMP issues, the oil system is perfectly fine. Knowing what your oil temps in the pan are is about as worthless IMO as knowing what your temps are inside the coolers. The only thing that is important is knowing the temperature of the oil going into the motor.

rotarygod

The oil has got about 8" of free fall within a very hot environment to cool down in. I don't think it's giving up a measurable amount of heat in that time.

rotarygod

I know it changes through the coolers depending on airflow through them. The worst case scenario should be 250*F. It shouldn't be a target to aim for. If we top that at idle but nowhere else, we know that we need to find a way to gain airflow through the coolers at idle. If it's fine at idle but at high speeds and rpms the oil gets too hot, we know we need to beef up the coolers or make efficient ducting to them. The oil isn't going to get too cold. The thermostat will ensure that.

rotarygod

Not quite but close. It is either hottest in the rotors or the bearings. When the oil leaves these areas, it drains straight down into the pan which is only a distance of a few inches. That's the first location after it gets collected into one area that we can get a temperature reading from and it is as close as we can get to the hottest parts of the engine. It's definitely close enough.

A problem with monitoring temps going into the engine is that we have no way of knowing how hot the hottest parts of the engine are getting to. What if oil entering was at 200*F but oil in the pan was 300*F? This isn't the case but how would anyone know. Average temps will fluctuate anywhere in the engine with changes in cooler efficiency regardless. The only difference with taking a reading from the pan is that we will know the highest temps and that is what matters. We can't determine that anywhere else.

PhillipM

However it's cooled by the mass of oil it land in in the pan, which is cooled by the engine block + the surface area contact with the pan, like I said, it is slightly cooler than the peak, we've got sensors both before and after the oil cooler, but none in the pan yet, might fit one and see.

If you do, watch what happens when you drive at 4-7krpm, and then what happens when you drive at 6-9krpm, it'll certainly show you how much extra heat is there...

olddragger

iTrader: (3)

or just control the overall temps and the oil temp will follow? Anyone ever seen a 200F coolant temp and an oil temp of 230-240F? i know on my car it isnt but maybe someone else has this?
OD

ASH8

I think we can come to the conclusion that everything between Mazda's NA (Naturally Aspirated) Rotary Engines used in the Series 1 RX-8 and the 1985-1989 FC RX-7 are the same, Engine and Rotor Bearings, Oil Pump and oil pressure, Oil Filter and Engine By-Pass Valves plus anything else that distributes or sprays engine oil for Internal Lubrication are the same when engine reaches "normal" operating temperatures..

Therefore there are only 3 other "Design Features" and Parts that are not the same.

1. Oil Recommendations (Viscosity/Temperature Range) listed in Owners manual.
2. Oil Coolers.
3. Length of Oil Cooler Lines.

************************************************** ************

So going into more detail...

1. I will leave this subject matter alone, been done to death.

2. The FC RX-7 only has ONE Oil Cooler, and that is a small one in height that is fitted directly under the cars Radiator which matches the same radiator width.
Keep in mind the "Cooling Air Flow" is constant/variable via a Viscous Bladed Cooling Fan running off the engine via a belt.
The RX-8 (in most cases) manuals had two Oil Coolers at the sides and front (under Headlights) with no cooling fan assist.

3. RX-8 has "Longer" Oil lines and twice the number of these longer supply and return Oil Lines, 4 for RX-8 and 2 for FC RX-7.

************************************************** **************

To put it simply, as we know the longer say a "Garden Hose" is in length the less pressure or water volume will move or "recirculate", apply this thought crudely to a cars Oil Pressure and Oil Cooling System.

So, does the RX-8 suffer from not enough oil pressure or flow through the oil coolers because of the Oil Pumps capacity?..I would say... yes.

The Series 1 RX-8 is the first time Mazda had installed 2 Outer and Front mounted Oil Coolers without increasing the Oil Pumps capacity or output or pressure!

The ONLY other export Mazda RX- to have two Oil Coolers in a similar layout and design to the RX-8 was the 1992-2002 FD RX-7, BUT, the FD RX-7 (Turbo) has a Different Oil Pump, and a Different Oil Pressure Regulator Valve Spring.
The FD RX-7 uses the same Oil Pump as the FC Turbo RX-7.

BUT the FC RX-7 Turbo and FC NA keep the same Oil Pressure Regulator (same in the S1 RX-8) and has the same single Oil Cooler under the Radiator, plus the FC RX-7 Turbo has an additional "Electric" Cooling Fan and Motor mounted on the other side of the radiator.

So my conclusion...Mazda really stuffed up in the Series I RX-8.
There is just not enough oil pressure or oil volume circulating through the entire engine/system for oil lubrication and oil cooling.

The solution??, while practicality and cost wise S1 RX-8 owners can not migrate or install the different Series II Oil Pump System, But, you could change the By-Pass Regulator inside the Sump Pan which is located on the rear Iron Housing to the one used on the FD RX-7, and or modify the Regulator spring so it will hold Oil Pressure Longer before the By-Pass Valve Opens..

Please GUYS, I am not trying to put Dirt on your model RX-8...I love them ALL..

But again, I am trying to find a solution that may help improved reliability.

It would be interesting to know if MNAO's re-man plant are changing oil pumps or valves....they should be...at the very least change over to the FD and FC Turbo Oil Pumps.

9krpmrx8

iTrader: (46)

HMMMM. Anyone have pis of the oil cooler feed and return lines readily available??

ASH8

Here you go, this is the best I can do, from parts manual... ( see RED Lines)

One is of FC RX-7, the other FE RX-8 (S1)...

9krpmrx8

iTrader: (46)

Thanks. So, the feed and the return are on the same side of the block as the spark plugs?

Flashwing

I have seen this but it was due to my cooling system working much better than the oil coolers were.

Last time I seriously overheated my oil temperatures (around 240 degrees) it was on one of the canyon runs here in Phoenix. Very tight turns so I spend most of my time in upper 2nd gear and 3rd gear.

I let off seeing 240 degrees and my water temps came down right away. Oil, as usual, was heat soaked.

ASH8

YES, the OIL feed is via a Banjo fitting line bolted to the left lower side of the front timing Cover..oil is fed by the Oil Pump.

The Return comes back on the same left side of engine and this line/hose connects just under the Oil Filter Body Alloy Neck.

nycgps

iTrader: (1)

Should I go out and take a pic of my FC's oil cooler lines or something ?

ayrton012

Yes, yes, yes. I think the same for about a month.

We have to increase the MAX oil pressure. Maybe our pump has the higher pressure possibility, so enough to change the bypass valve, valves. It's not enough if we want to force the AVERAGE oil pressure (flow). In this case we have to change the pump itself.

...and we have to plug in the e-shaft's draining holes (at the pellet) , to shorten the time while the oil flow builds up in the bearings, after startup.

PhillipM

Yes.

Had coolant at 95*c (~200F) and the oil heading past 120*c (250F) regularly when we were on the same size coolers as a stock car, which is what I was referring to earlier for someone with a temperature gauge to watch what happens if you start driving in the 6-9krpm range instead of the 4-7krpm range.

When we we're just on test and short-shifting at 7krpm, the oil temps would sit in line with the coolant at 200F, even with full throttle, as soon as you start using that last 2krpm, they shoot up faster than an eagle with a Saturn 5 rocket up its ****.

olddragger

iTrader: (3)

interesting on the coolant/oil temps relationships. Those that have seen this range were all doing the driving that we all like to do
I know that the corvettes all see 250F oil temps on the track without any concern--so the oil itself seems to be able to take it ?

Ash--once again you are the man. A real parts man to point all this out and offer possible solutions. For anyone doing a rebuild the 09 oil pump would be a good choice.
So in essence we have figued out why Mazda increased the oil supply/ flow for the 09--.
The clearances are basically the same as earier models? And they recommended 5/20w oil.
Much more distance involved resulting in decreased pressure?
E shaft oil supply could be better?
Who at mazda did this --its just common sense!!
Glad I have a Rick E engine who has done some work on this.
Damn good info.
OD

PhillipM

It's going to be even hotter than that when it's passing through the rotors and bearings though - my sensors are only before + after on the oil cooler.

It really does all point to simply not enough oil flow through the system, if the '09 pump fits, I'd be going with you two and be fitting one on a rebuild for a standard car.

I think we're getting away with it because we're cooling the oil so far before it gets fed into the engine, frequent changes and using decent synthetics. Band aid solution, as it were.

onefatsurfer

Well... if film strength is what's separating the bearings (it is) and the heat of the engine is going too high and breaking down the oil (which, it also is) then a higher viscosity synthetic + premix + increasing OMP rates (or, using a sohn adapter, ideally) should be sufficient to solve most of the problems. When the oil breaks down, it'll still have better film strength to keep the bearings apart than if we used straight 5w20, and the synthetic won't break down as quickly as the dino oil. The thicker oil will have a tougher time getting past the OMP nozzles, so increasing the OMP rates and using premix would be a must. Ideal fix would be to put a higher displacement pump in, as that would prevent cold start issues too. Too bad we don't really have that option at the moment

PhillipM

The higher viscosity will help, because when it's breaking down it's still going to be somewhere near the viscosity you actually want - but if the breakdown is due to heat, then be aware that many of the additives will be mullered by then anyway, the surfectants especially.
I'd see what sort of temperatures you are getting on the oil entering the engine and see if there's anything you can do there too.

olddragger

iTrader: (3)

still you need the proper amount of oil to get to the places requiring lubrication and cooling. It cant do its job unless enough of it is there? We need more volume of the proper oil? Right?
The omp is volume driven--viscosity does not affect it.
Premix is a different animal because its deliverly system has to go through smaller filters and the fuel system/engine is sensitive to pressure changes?
Now i am dizzy and have to set down.
OD

PhillipM

Ideally you'd want a pump delivering more oil full stop, yes.

rotarygod

You are WAY overthinking this. Show me a hotter place to measure the oil at. I'm willing to bet that any heat lost from peak temps to the oil pan are within 5*F. Not enough to matter. The oil pan isn't holding a swimming pool worth of hot oil. It is collecting it so it can recirculate. Yes you lose a little heat there through the pan itself but overall not much. The higher the rpms, the faster the oil gets circulated and the hotter the temps will be. Measuring temps after the oil cooler doesn't seem to make sense. Measuring it at the hottest point possible to get a reading, which is the pan, does.