Smitter

Hey Guys,
i am in the process of installing a dual oil cooler setup, but for ease of installation and to save a few bucks i want to skimp out on the thermostat. i cant really see it being necessary thinking that the oil temps will never drop below a safe operating level once warmed up. The coldest ambient temps the car would see would be around 50f. Opinions and experiences please

Also, what would be the scale of safe operating temps for oil? from what i gathered anywhere between 140-210 should be safe for spirited driving?

Marcel Burkett

hot oil press @3500rpm+ = 110psi + , cold oil press will be a lot more !!!!!!!!!! , coolers are designed for 200psi . Do what the factory did , put two , one per cooler !!!!!!!! , thats what I did .

Smitter

i dont see 110+ psi @ 3500 rpm, whatever though, oil pressure is errelavant to this thread. if the oil is warm enough the pressure will be where it should be. the factory put thermostats in maybe under the pretences that people would be winter driving there cars, some people do, i do not.

whats the sense on having a thermostat if it opens @ 140f and stays open the entire time the car is running? doesnt make alot of sense to me

BLUE TII

iTrader: (9)

The oil pressure is NOT irrelevant to the thread.

Without a thermostat to bypass the oil when cold it will INFLATE your oil cooler with high pressure. Looks like someone blew it up like a balloon.

You get to learn from other forum members mistakes.

Smitter

^^ if the oil temps are in operating range, there will be no harm done from any substantial pressure, you could do the same damage your claiming with a thermostat just as easy if your not gonna let the oil get up to operating temperature before driving the car. i dont believe the thermostats will even help in the warm up process if the car is sitting and at an idle. with no air moving through the coolers they cant cool anything, my concern is if the oil would stay above 140f while light throttle driving in 50f ambient temps. i believe they probably would, so a thermostat shouldnt be necessary and if nothing else just another component to fail.

fd_neal

iTrader: (4)

guys how can pressure be a problem... the cars have a high pressure bypass, limiting top pressure.

Minimum oil temps are a big issue tho, IMO 140 is way to cold for your oil. I wont get into the throttle if mine is below 150 and wont really get into it untill 185. My T-stat is 185, on the street/highway cruise my oil temps sit at 185 on the hottest summer days around here i might see 200. on the track is a different story, hot days ill see 240 cool days ill see 230. <- 15 minute full road course sessions.

On my setup without the t-stat i think id have a hard time getting the oil up to temp on the street on anything but really hot days. My setup is a very well ducted dual cooler setup.

swilson@assetworks.com

iTrader: (13)

Put an oil temp gauge on the car.
Then decide if you need a thermostat or not based on the observed temps.
The thermostat I have opens at 170 F even though it is rated at 180.

Smitter

thx for the info guys. i have an oil temp gauge in the car, that is a necessity for any high hp rotary imo(epsecially if one chooses not to run a themostat), i agree 140 is too cool, i was just using that figure cause i thought that was what the stock thermostat opened at. anywhere between 170-210 shoud be ideal operating temps. 240 is way to hot from what i am being told

fd_neal

iTrader: (4)

240 is hot; however, isnt out of line. Mazda actually reccomends 240 as the max oil temp in their race motors. You do need to run a quality oil tho.

For comparrison, a friend that i race with owns a bone stock ZO6 and he will see upwards of 270 on the same days that i see 240, and another friend with a bone stock BMW 135 will sit around 220 on the street and 240 while running at the track and BMW will put the car into limp mode at 270.

Hot oil lubricates better than cool oil, the big difference with our cars is they rely much more heavily on oil for cooling than a piston motor so we cant let it get to hot.

Smitter

is it safe to compare the rotary oil temps to piston engines oil temps, i had a motor fairlure recently and my builder is blaming it mainly on oil temps being too high (240F)
oil control rings are jellowed, corner seal springs & side seal springs are flatened

arghx

iTrader: (3)

on my nonturbo FC the oil temps were regularly lower than my water temps, that was with the stock radiator and the stock FC oil cooler, which is at least as big as two FD oil coolers. In the winter especially, I would be steady at 180ish water temp and oil temps would be in the 150's. oil temps were measured at the oil filler pedestal.

thetech

iTrader: (1)

Bear in mind that is at the pan; at the filter pedestal where most people seem to measure it should be at least 10* cooler (if not more).

fd_neal

iTrader: (4)

If mazda will state 240 as an acceptable oil temp in a race then im 100% willing to run it in a race.

Alot of people will comment that hot oil will wear your motor faster, all engine oils lubricate better when hot, and good oil wont get thermal breakdown untill around 300 *f, so the trick is running the right viscosity for the temp range your running.

The big difference between rotaty and piston for oil temps is that rotary heavily relys on the oil for cooling where piston motors not nearly as much. Thus max temps are a big deal (as are min temps) Mazda has stated up to 210 coolant and 240 for oil in a race application, this is enough to give me confidence that mazda parts will be durable at these temps. often looked past is your oil should reach around 210 to cook off the condensation.

I forgot about this, in my old rx8, bone stock, with the ac on in traffic my oil would climb to 230.

The question is if you should run a thermostat, and that answer is yes, gets your oil up to temp faster and will reduce engine wear from running cool oil. I think mine cost me 100bucks, money well spent. But as said if you go without one watch your gauge and get one if you need it.

fd_neal

iTrader: (4)

Ive got my sensor on the hot side of my t stat. It should be reading the hottest oil in the system. with that said better cooling is in the works for next season, id like to get on the track and not have to worry about anything more than my driving. Ideally id like my oil to sit 215-225 on track and water to sit 185-195. As it sits ive seen up to 205 water and 240 oil.

thetech

iTrader: (1)

Definitely is worth redoing your system if you have concerns about it. I am just finishing up the same thing right now:

Smitter

yeah my temp sensor is in the pedestal aswell, 240F after the cooler system, way to hot for sustaining any kind of load, the motor blew at 130mph in 4th gear, thats a little different then seeing temps @ 230F with the ac on in traffic.

the point about the oil warming up faster with a thermostat is a moot point if the car sits and idles before driving, a oil cooler is doing nothing if the car is not moving. its really not a big deal anyway if the car takes an extra few minutes to warm up

kenn_chan

Put a thermostat in, I run two huge coolers for when I am at the track. When daily driving one of my thermostats went bad and jammed open (default) and with the bad T-stat it over cooled the oil.

I let it warm up to operating temps and then drove but 5 minutes into driving and my oil temps are back below 140, hell i saw them drop as low as 100 prior to getting t-stats replaced.

Kenn

Smitter

^^hey kenn, thx for the info, how big are the coolers your running, can u post a pic. that is definetly something to watch out for, but i think i really wanna try with no t-stat, if it doesnt work i will then install one. i will report back with what i find. but it wont be until spring.

Rx7_Nut13B

iTrader: (1)

I am in south Texas (AKA HELL in the summer) I run twin 19 row coolers without a T-stat, I have had some cooler oil temps during the night, but also i have a super electric cooling system without a T-stat also.

Yes cooler oil will have increased pressure, like said above that is what the front cover bypass is for, to protect the lines and coolers from pressure spikes. My Earl Coolers are rated @ 175psi with Burst pressure around 375psi, and the highest i have logged even when really cool was 150ish, then the lines are rated @ 1000psi.

But to each there own, it really depends on your driving and where you live

kenn_chan

I do not have photos right now, but my coolers are 2x12x10 and are both directly in the airstream at the front bumper. Its a custome one off setup, and next time I will grab photos

Smitter

UPDATE:

The car is back on the road. i opted to go with one earls 34 row oilcooler. (11x10x2 are the demensions) and no thermostat. driving the car in the daytime (70F) under light load. Oil temps range from 180f to 200f. i have seen them climb to about 210-215f while stuck in traffic. they quickly return to below 200f when moving again.

driving at night (50f) at highway cruising speeds oil temps have dropped as low as 150f. but under light load and some boost pulls it hovers around 170-180f. i am still unsure if a thermostat will benefit my setup. does it do any harm to the engine to be cruising with temps at 150f? oil temp sensor is still located at the filter pedastal.

Barry Bordes

When you start your cold engine with heavy weight oils the filter is by-passed and contaminants are sent to your bearings and turbo. You want to heat the oil as fast as possible.

Mazda’s specification is for the filter to by-pass when it sees a 14 psi differential pressure across the filter element (and the finer the filter, the higher differential). The relief valve is made into the filter. Unless you are using a remote full flow filter our filter continues to by-pass contaminants till the oil is warm.

I worked for an oil company on turbine and reciprocal powered aircraft. On the engines and transmissions we had impending by-pass indicators on the filter head to indicate when the filter is becoming contaminated. On cold mornings (below 40º F they would “pop” regularly because of the thick oil. This was with 100% synthetic.

I try to keep my oil pressure below 100 psi on starts and will not move the car till I have 50º C oil temp.

Barry

Gorilla RE

iTrader: (1)

Barry,

I agree with needing a t-stat for start up and initial heating of the oil and understand what the by-pass is doing. But to answer the OP question I believe that after the initial oil heating a t-stat is not needed, the oil cant be kept cool enough (especially in a race car). 90% of rotary users take oil temp readings from the oil filter pedestal, and it's usually about 215-240* operating temp. But what do you think the oil temp is on the inside of the rotors? 300*, 400*.... I'd say close to twice as hot as operating. So much wasted thermo energy is being taken here.

If you are on a race track, I believe you couldn't have enough oil coolers on the car to keep the temp optimal. My vote is no t-stat.

-J

Barry Bordes

J,
I know it's hard for us to remember winter right now as hot as it is, but the oil still bypasses the filter during starts in the summer. We can probably get by with a standing warm up (this idling would not the best for cold range sparkplugs). The colder it is, the longer the oil will bypass the filter with trash going to your bearings and turbo. It happens with ever start to some extent.

Also, most people think of a radiator type of thermostat being inline and restricting the flow of oil. As you remember on the stock oil cooler only a side bypass is closed. There is no restriction to flow. It is totally closed by 150ºF (65º C).

I would agree that without a thermostat there is one less chance of a failing part. (A side note, on aircraft it is referred to as a vernatherm.)

Barry

Smitter

thx for the replies guys.

so am i to understand that the filter gets bypassed during warm up? what is mazda's reasoning for this? at what temperature would the oil start to flow through the filter? regardless though. the oil should take just aslong to warm up with a thermostat as without if the car is at a stand still, correct? in my opinion without air moving throught the oil cooler the oil cant be cooled, therefore a thermostat is not going to assist in warming the oil while the car is at a stand still.
My question is this. how cool can u let the oil get while highway crusing the car? if its double inside the rotors, 150f at the pedestal is nothing to worry about???