Oil cooler thermostat?
 

Maybe it's already answered, but I found the next sentence in a German RX-8 (SE) service manual. I did not find this info in any other english serv. man.

If it means that there is a 194F opening temp thermostat valve in the oil coolers, maybe it could be the reason for some of the overheated engine, and the high oil temps.

Some thoughts:
There is no cell when this thermo valve goes wrong.
If the thermo valve open later (went wrong), the oil temp will be too high and the oil will be too thin (bearing wear).
Who knows when the thermo valve goes wrong, does it stay opened or closed mode?

In winter (europe) my oil coolers are only warm when the engine is on idle for a while and the car is standing. If the car was moving before, the coolers are cold immediate after stopping. I could check it with my hand after stopping. Even in summer my cooler's thermostats are closed a lot of times (checked after stopping), when the engine warm.

Oh good find. However Rotarys run hot anyway. Always have.
You know Jeff (MM) can read that stuff (German) really good. PM him.
But why would it be in that book and not the US book???
Keep us posted!

MM's post box exceeded the limit, so I sent a mail to him.

Just for confidence, the information comes from the German Mazda RX-8 (SE) Trainingshandbuch 11/2003.
It's a book in my hands, but I don't speak German.

Well, German is not my primary language, but this is what it says:

"An integrated thermostat allows oil with a temperature over 90°C (194°F) through the oil cooler."

So where is this thermostat or valve?

Has Paul at Mazmart seen a valve on the oil cooler?

All RX-8s have them. Its in the oil cooler itself.
IIRC, all of the contemporary rotary Mazdas had thermostats in their oil coolers.
90°C is troubling, though.

Then there is Easy answer to running hot.

Correct?

No, probably not.
His oil temps are never as high as his water temps when he begins to overheat.

I'm in the same boat. (Though my issues are due to the intercooler blocking airflow to the rad.)
Thermostats in the oil coolers is a good thing in most places, I would just like to see it open at 175°F.

Is it true, that all of the RX-7 FC-FD oil coolers's thermostat opens at 149F ?

Why the Renesis has so much higher (194F) temp thermostat?

dont concern yourself with oil temps---not an issue. the oil temps will follow the coolant temps more or less. address coolant temps. Mazda does not want oil flowing through the coolers at too cool of a temp due to possible plugging.
OD

Huh?
Where do you think the water gets half of its heat from?
Oil doesn't follow water - water follows oil!

umm... nice 69 avitar!

Hmmm, subscribing. Can the oil cooler be upgraded?

thats why you should pay more attention to the coolant temps---and if you get it down the oil temp will follow!
Oil doesnt play a part in cooling a large part of the engine whereas the coolant does---concentrate on the coolant. If you concentrate on just the oil---well ok go ahead.
olddragger

As I said - other way around.

FC oil cooler thermostats started opening at between 140F and 149F (60-65C), the same temp that the E-shaft thermo pellet opened on a FC.

On the FC, 30% of the cooling was by the oil... is the FE water cooling system that much better that number is reduced?

In Japan, some shop has them.

you can always go get universial kit and fit it your self.

if the oil is doing 30 % of the cooling then the coolant is doing 70%. which do you think will respond to upgrades better? which will have the most influence on the other?
to see one difference between the engines look at the housings on the earlier models versus the renasis and you will see that the areas around the sparkplugs has a much bigger area for coolant to pass through for example.
the twin oil coolers on the rx8 are pretty good--the oil system has the capacity to cool the oil if it is not asked to cool more than its share. The inadequate coolant system does just that. The coolant temps on a 90+ day on an oem car at low speed can get to 230F easily. the oil will be at around 210F. To get the oil temps down from that you are going to have to create enough cooling capacity to influence the coolant temps--that will be a pretty big job. Now if you add just a little coolant cooling capacity to bring that temp down to 200--then the oil will drop down to 180 easily.
would you rather work on the system that has the lesser impact on the result you are seeking?
And dont forget--the oil will do its job at 250F+ coolant will not!
It does have to be a balance--you dont want much difference between the two.
enough said.
olddragger

Think you are missing the point. Modifying the cooling on the car is not a one thing or the other. On a rotary engine it only makes sense that if you are upgrading one, that you also at least look at upgrading the other.

However it makes no sense what so ever to say, "I only want to upgrade the radiator" if you are having temp issues. If you are having temp issues you should look at every thing you can, to help.

Its not like changing the oil cooler thermostat and eshaft thermo valve is going to solve anything, but in conjunction with other modifications it may lead to better coolant, oil and engine life. Now with a piston engine, the oil does not provide even 5% of the cooling, so your comments fit that idea perfect. Why waste the time even looking at oil cooling if you are not affecting anything. On piston engines that use an oil cooler, it is more for oil life than cooling of the engine.

But on a rotary, its not, and this is not a one thing or another issue. Sure if you can solve the issue with a bigger 3 row radiator, then you are done. But if not, if you run the oil temp back down at 180 instead of 210, that might be the extra kick that helps.

Now again, don't get me wrong. If you are having overheating issues, just changing the oil cooler thermostat is not going to solve anything...But how much less viscosity and oil break down.. how much would be reduced by dropping that oil 10 or 20 degrees?

and if you are running a h20 thermostat that works right at 180 deg. the with some extra water cooling. both the problems are solved..

that is how olddragger fixed the problem..

beers :beer:

Hey guys, I asked this before but no one really gave me an answer, What about using a water or oil pool? will that help with cooling? I know some GT and other race cars use them.
-Gil

icemark--you are absolutely correct--everything should be looked at. And the full range balance (warm up, wot applications etc) between the oil temps and the coolant temps have to be considered.
In looking at all --i found my solution by simply adding a small secondary radiator placed below the front support member directly in the air flow
https://www.rx8club.com/attachment.p...1&d=1235846259
see pic--this little thing with a couple of other mods will fix the cooling problem(except for the desert guys with no humidity in the air.
olddragger

OD can you post a larger pic? or pm it to me and I will post it. I cant see shat in that small attachment.
-Gil

You don't say, so are you talking oil or water rad you added? Your pic is not much bigger than an avatar, can you post one a bit larger so we can see what you added?

a couple little other things? Can you pls be a bit more specific?

ok here goes guys
https://www.rx8club.com/attachment.p...1&d=1235924191
if this doesnt work i will take some new ones
od

try again--yall know my rep with pics now
https://www.rx8club.com/attachment.p...1&d=1235925720
hope this works
OD

ok i have the pics up now--yall like those Hehe.
the small radiator from summit racing 21x7.5 inches 3/8 tubes
it is feed by the return heater hose--(it is a non thermostatically fed system) and it returns to the thermostat housing as the heater hose normally do.
homemade hangers from aluminum stock available at lowes/homedepo etc. mounts to the front bumper support.
upgraded water pump(mazmarts) and a 60/40 coolant blend in the summer months. Stock thermostat unless the temps are in the high 90's and i am headed to the track--i then have a custom 180 thermostat barrell type that i use. Mazmart is reportedly thinking about building a stock replacement thermostat that fully opens at 180F--but not yet.
removed the front rotory symbol for better airflow.
thats it
youre temps coolant and oil will be fine.
airflow is the key and this puts the cooler right where it is needed. for those that dont want to do the work etc--Pettit is going to sell a kit almost like this but it is mounted in the airdam belly pan.
olddragger

^ This is a great idea - if you want the car to run even hotter.

You take a smallish rad, saturate it with hot water and then us it to simultaneously reduce airflow to the main rad and heat that reduced airflow up to the temp of the coolant in the first place.
Brilliant.

The 70/30 cooling comment is still missing the point.
The oil cooling system is responsible for shedding a smaller amount of heat than the rad because of the thermal properties of oil versus water.
Oil is slow to give up its heat.
And therein lies the problem.
If the oil temps rise to coolant overheat temps, you will have an impossible chore before you in getting the water temps under control.
However, if you get the oil temps down to as close as possible to minimum operating temperature, keeping coolant temps under control is a breeze.

MM dude --give me a break. Wait a minute--no dont give me a break--dont want one, dont expect one. I dont even expect any objectivity.
Bottom line--this works for me. My data proves this.
Not only do I put this small cooler in front but the pettit a/w intercoolers are behind it--then the a/c condenser is behind that---then the radiator.
Essentially --i have been just called a liar. That dude has crossed the line with me
So I have had enough. If anyone wants any additional info--data etc just pm me please. If not that's ok --just trying to share what I have done and what has worked for me
best wish's MM. no more
olddragger

Your datapoints are understood.
Unfortunately, they contradict quite a few other datapoints gathered by other vehicles in the field.
No one is calling you a liar. You are just misguided.

Exactly! Thanks for explaining it better than I even approached.

:banghead:

I'd like to ask a couple questions...and I'm asking for arguements one way or the other.

In our car, which system dissapates more heat (BTUs)? The oil system or water system? I've never seen any data, and it would be helpful.

We have a nice radiator, but more expense was taken cooling oil with dual oil coolers. Does that mean more benefit would be gained from more oil cooling 1st over water?

Let's say yes. Would simply improving the air flow provide more improvement than trying to add yet more radiator? How about removing the inside fender well plastic piece in the front. It's a separate piece, just takes a small screwdriver and 5 minutes. Would that freeflow matter enough on track events?

What happens when you say use a Mazdaspeed style bumper? Does that increase airflow - both water and oil significantly enough to matter. Could that be the easiest 1st cooling mod?

It would be ideal to once and for all determine some system of improvement, hopefully passive and easy not requiring additional plumbing $$$.

So I'm thinking, MS bumper, remove/redesign the rear fender well air outlet panel would do the trick? Is that crazy easy or simplistic?

I think yes, but the bigger openings increase the drag of the car, which of course don't relate so much to the overheating problem.

More question:

What are the average oil temps in an FC, FD, when the engine hot? Is there a huge difference between the Renesis, and them?

explaining what? its what everyone is dealing with when they buy a Rotary. Think of it like this; when you cock with oil it will hold a temp of oh lets just say 400F. Reuse that oil and it will hold a temp of oh 200F. This is just a example. But you get the point. Ok now that same gos for brake fluid. People that dont know this will just say uhh I never heard of that. But know you have and know you should start thinking about it and how all things liquid brake down over time with heat and dont block heat like they use to the first time they where used. Thats why I stay ontop of my oil changes and flush it.

The drag will be so minimal at rule road speeds its no big deal. However at high speeds the charged air is will find a way out of the engine bay. Just look into how the NASCAR's front, hood, and fenders are set up. Also open wheel race cars engines are closed in. All Rotarys run hot and drink oil and gas lol but think of it like this; Oil temps: If 30c=86f when moded FD's sit in traffic in 86f they get up to 194f. Now depending on your driving freeway driving will be about 140f to 194f.
I think water temps will be about 18 degrees more. Keep in mind all this is give or take and based on location and mods. But you get a good idea.

1. Oil.
2. No big deal. Lots of exotic cars have this set up IE: 911. Second part of this question ref back to question one.
3. Yes and no. See I removed that plastic's that are right behind my oil coolers. However that dont mean more air is going to flow better throgh the oil coolers. What to keep you stuff cool? buy and use a radiator comb to keep your fins straight.
4. Yes the MS front will increase air flow. Will it cool the water significantly? no and no.
6. Good luck but I can tell you this; I dont have the MS front, plan on gettong one soon, I did remove the plastic's behind the oil coolers, gaped my hood and did the TB by pass. All 3 will help you out a lot. Just doing one. I dont know.

Holy crap that was a lot of nonsense.

Whoa, there's some seriously bad information going on in this thread.

Being in one of the hottest climates in the US, I've spent a lot of time looking into cooling so this is a subject, thankfully, I've had a lot of experience with.

Let's get some facts straight. Oil is NOT the primary heat reducing agent in the coolant system. If that was the case you'd be using oil and not water to cool the motor. The difference is that oil will absorb about 1/3 of the engine heat and thus needed to have coolers in order to keep oil temperatures under control.

Oil temperature is the most important temperature of the two however. If you had 230 degree water temps with 260 degree oil temps you're motor is about to blow if it hasn't blown already.

If you have 230 degree oil temps but your water temps are 260 degrees you're still in a danger zone regarding detonation but your motor's chances of survival are greater than the previous situation.

One of the best methods I've seen employed is using an oil cooler from a 1st gen RX7 and placing it in line with the other 2 coolers. The oil lines simply link one cooler to the other which are placed in series. This would add extra cooling capacity as well as increasing the total amount of oil in the system.

I've also been running the Greddy oil pan for quite a while. It's cooling capability at idle is probably not very good being a foot off the ground but it increases the oil capacity of the RX8 by 1.5 quarts which does help.

Overall, my cooling setup consists of the following:

Greddy Oil Pan
Koyo Radiator
Mazmart water pump
Distilled water w/ 2 bottles of water wetter
SEIBON vented hood

I had a rare opportunity to race my RX8 on the track when it was about 105 degrees outside and about 140 degrees on the track itself. I was able to stay full throttle during the training session much longer than most vehicles including the other RX8's.

The problem was once the oil system became heat saturated my racing session was over. Oil doesn't give up heat easily and even after taking it easy for a couple laps the oil system didn't recover but a few degrees. The water system came right back into safe zones however.

Other problems involve sealing the area around the radiator. Too much cold air can escape around the sides since the resistance is less.

Frankly I find the notion of secondary radiators a waste of time. There are radiators on the market which are large enough to do the job of cooling the RX8 and using a secondary is totally unnecessary except maybe as a cost saving measure.

I had to come back here. People who know me, know that i dont lie about this stuff and I freely share with others whatever I find out.
the radiator on our cars would probably be ok if it was directed more into the airflow in a more direct manner, but it is not. The rear of the radiator is also partially blocked by the battery box and aircleaner stuff. heck there is poor airflow through it in comparison with an upright rad directly in the airstream.
I will challange anyone that says this set up I have does not work in my area. The desert area folks have a totally differant enviroment and this mod may not do them much good--they dont have much humidity in the air to work with and humidity is a good thing when it comes to cooling. Their approach has to be different.
I have also ran on a 105F day and the pavement measured at 140F--alternator got so hot that the edges of the belt actually melted. engine coolant temps at MAX when i had to hold the car for a little over 7K was at 204---oil temps at 196. Once i was able to vary rpms again temps stabilized at 194-198--oil temps the same. If anyone has coolant temps of 260F with this engine then you have BIG probs.
Before I did this mod, on track, oil temps would get hotter than coolant--i have seen oil temps at 230F while coolant was at 220--before my mod. Most of the rx8's that have gauges that run track in my area will tell you the same--its not the usual case but on red flag times etc it does happen.
My street temps are in the 170-180F--traffic doesnt matter. if setting still with the a/c on and a hot high 90F day it will go to a low 190 and then cool off when you can move again.
I disagree that our oil temps are the most important in preventing damage to this engine.
I will also challange anyone to produce an oil temp of 250+ in our cars while the coolant temp is at less than 200F. Why?---because they work together--and the coolant has a much more profound affect on the overall temps of the engine. It will not allow that much of a difference between the too. If you coolant is already at 230 --again you have problems.

Airflow is a component of cooling that cannot be ignored. This was the easiest and the less expensive way that I could think off to fix my problem.
olddragger

by the way--i do not want this to sound like the BHR radiator doesnt work. I know some people who have one and are vrey staitsfied with it. It is a much better design than oem and has a much better cooling capacity than the oem.
Some people would not like to do to their car what i have. The BHR rad is a great solution that appears oem in the install etc.
I would NOT endorse the Kyroso one.
Those are the only 2 rads that I know anything about. Their may be other good ones out there.
People get the wrong ideas easliy and I just wanted to clarify.
OD

Why are you hung up on the idea that someone thinks you are lying?
All I'm saying is one data point doesn't make a sample.

No one is discrediting your findings.
Unfortunately, they run contrary to the larger body of data, that's all.

I don't think anyone is going to confuse vegetable oil with motor oil. One, you want to you want to retain heat as much as possible and the other too reject heat as much as possible...

And with vegetable oils, the loss of temperature holding is due to contamination of the oil stock, with food stock.

Hmm, actually again, you seem to be missing that the only reason that brake fluids break down is again due to contamination usually by absorption of water. The boiling point lowering on brake fluid is not due to repeated heat cycles, but rather absorption of moisture which lowers the fluids capability to resist boiling.

Of course most DOT3,4 and 5.1 brake fluids are designed to absorb water to help reduce corrosion, so regular changes are required to maintain the anti-boil properties and remove the contamination from water, so that full brake compression is possible with limited to no fluid compression. This is why you change your brake fluid every 2 years. To remove the absorbed moisture from the system.

Oil viscosity break down on the other hand comes from contamination (blow by products) and shear and heat.

So not sure why you are bringing that up. Clearly every example you used, well they don't follow anything logical.

So getting back to the point, reduce the heat of the oil, and you reduce the temp battle in the engine between the oil and the water, and you reduce the possibility of viscosity break down from heat.

Umm okay, then explain how you can run 100 miles without a oil cooler, but can't run 100 miles without a radiator.

:arcadefre

Ok it was a bad example but you get my point. They breakdown over time with heat. You know as well as I do that oil dont last for ever so dont try to pull that bull shit on me.

No. Why dont you and Jeff tell me. You know thats bull shit. You can only run the quarter mile with out any oil coolers on a RX-7 and RX-8 has about the same heat issues as they do.
So I tell you what, I will by the by pass piping from home depot and send it to you all of it for free. You drive your car for 100 miles this summer and let me know how your temps are :rofl:

Gil - you are really out of your depth here. Just let it go.

70% of heat rejection is through the radiator... enough with the oil dissipating more BS

ok-- my findings are contrary to a large body of data -- what data? I dont know of but one other car that has done this (by the way he had just as good as an affect as I)--so what data is being referred to?
I can answer myself-- because there is no other data than what we 2 have in evaluating this modification. You have to compare apples to apples.
It is what it is. Thats all.
I have to apologize to the originator of this thread--sorry it got turned around here. You had a good question and maybe we helped answering some of it?
I am so sure of this modification that this summer if there is anyone in the state of Georgia that does not believe me,--- do this modification--if it doesnt cool your engine temps (coolant and oil)
I will pay you back the money it cost you to do it. Now i will have to see the car and see the data--thats why i limit it to Georgia.
Someone come prove me wrong.
olddragger

You can't prove a negative.
The burden of proof always lies with the one asserting the claim.
Just sayin'.

course you can prove a negative--if anyone doubts that this modification doesnt work, put it on your car, if it doesnt work then they have proved me wrong.
its a "negative" or a "positive" depending on which side of the belief you are. Quit trying to abstract away from the focus.
The proof is in the data. I have the data. The data is either believed or proved wrong. Call or fold?
olddragger

Well actually if you could keep the oil clean and in normal operating temps, it would last forever (other than what is lost by seal seepage and use through the MOP).

Now you still would get the viscosity break down, but in that case typically the base stock would remain. For example if you had a 10W30, in most oils* you would end up with a 30W when the additive package got used up.

But the base stock pretty much would indeed last for ever, if you could keep the oil clean and in operating temps.

The problem of course is the same problem that happens in your cooking oil... contamination. The acids and gasoline and coolant that all seep into the oil through the combustion process contaminates the oil. Those are what the detergents in most oils are used for, but when they get used up, then it is your oil alone doing the work. If you could filter these out however, then you could use the oil pretty much forever. But the average car oil filter is just about useless for this part of cleaning/filtering.

This is what happens to your oil when you drop it off at your local auto parts store after an oil change and they recycle it. It sent to a refinery, gets cleaned, new additives are added and it is mixed up and sold back to you for use in your car all over again.

* Now Mobil 1 claims no additive package in their 10W30, so in theory using that oil you wouldn't even have to worry about the viscosity additives breaking down.