oil thermostat on OEM oil cooler
 

How does the oil thermostat on the OEM oil cooler function? I know that it blocks oil from getting cooled until it's heated to a certain temp.

The question is does it (1) block the flow of oil to the cooler entirely which would mean no oil would be flowing through the return line or does it (2) re-route oil within the cooler so it doesn't pass through the fins, but does go through return line.

The reason I ask is that if the answer is option 1 then you could run an aftermarket cooler after the stock cooler without needing an aftermarket thermostat.

I assume that the answer is actually option 2, but I don't actually know for sure.

its option 2. oil needs to run through the "oil cooler return line" to pass through the oil filter & lubricate the rear bearing

That's what I thought. Thanks.

Last time I checked, all of the lubrication for the motor is supplied through the cooling loop.

The thermostat is a bypass type that is open when cold to allow some, but not all, of the oil to bypass the cooler. As the temperature increases, the bypass closes causing all of the oil to flow through the cooler.

Has anyone verified the opening/full open (or I guess closed) temperatures of the bypass valve(s)? Is there one in each cooler? Reason I ask is that my oil is friggin freezing in the winter around here when I'm on the fwy steady-state crusing and it's less than 60*F outside... I live in So Cal, I can't imagine how cold it'd be if I drove it in Canada or someplace like that. OEM & ducted dual oil coolers on my car, 20W-50 dino oil. Seriously the oil temp @ the pan will drop down to 150*F... That means the oil going into the motor would be even COOLER. That is too cold for oil IMHO. Maybe I should run lighter weight oil in the winter.

Yes

It should be 150F or so. It's been that way for a long time. I wouldn't worry about it. I have measured similar temperatures at the oil filter pedestal. There have been owners who don't know two shits about oil cooler relief valves running these temperatures for years and years.

https://www.rx7club.com/attachment.p...1&d=1283891928

https://www.rx7club.com/attachment.p...1&d=1283891928

Good info guys, I should have RTFM. Thanks for chiming in!!

Be advised that the way the oil thermostat operates is as a bypass (which is true of most oil thermostats) meaning it does not shut off oil flow through the cooler; rather, it opens a passage that simply shunts the cooler and gives the oil a lower resistance return path to the engine. Note that some oil, however, will still flow through the cooler--and be cooled. Additionally, the thermostat also functions as a pressure relief for the cooler (hence the bypass differential pressure rating).

If you want to run warmer oil temps with a cool ambient, you could reduce or block airflow to one or both coolers as required.

where can one buy this 150F degree external oil cooler bypass valve?

There is nothing wrong with the temperature the stock oil cooler thermostats open at. It only becomes a cooling issue with modified cars that see hard use, especially on models with only one cooler because there isn't enough capacity. I recommend at minimum to add a set of R1 coolers or better yet SakeBomb Garage oil coolers. In the RX8 the stock thermostats don't fully open until nearly 230 degrees and those motors show far more wear in less miles than an rx7.

Sorry, I asked because I have an aftermarket oil cooler on my 84 FB. I ditched the beehive cooler. I just learned that the aftermarket oil coolers do not have the internal bypass valve. I'm basically running without a bypass. Oil is cooled constantly. I have the stock clutch fan as well. Should I be worried?

So if anyone knowns where to get an fairly priced aftermarket oil bypass valve that'd be great :)

If indeed oil is being cooled constantly that shouldn't make much of a difference. You really would just hate for it to be the other way (oil never getting cooled). Just means your engine will take longer to heat up fully. Only time I could really see it POTENTIALLY becoming a problem is during the winter when it's really really cold. Like, near zero temps. Realistically though, the radiator and cooling system should still regulate your engine temps so the oil being fairly cool shouldn't be that much of an issue.

Yes. I think what I need is an oil temp sensor to monitor the levels. I know it's hot to the touch going into the rad oil cooler. I'll get a pic.

Thanks for the into Italyn. I always let my engine warm up before a drive and make sure I got oil coming from my OMP. I'm in Canada and temps can into the signal digits during the night around this time of year. But I store it inside as well. It'll be soon time to winter store it.
I'll keep the oil cooler as is..the oil bypass unit would set be back $200+ Canadian dollars.
Maybe I'll run 10W-40 as well.. Ive been running 20W-50 castrol the past two years.

I just bought the same oil cooler as you. Its a nice oil cooler, I bought an external oil cooler bypass for mines but I didn't have enough fittings to run it. I will run my car without it to see how good it does. Over here it pretty warm so im worried of the oil getting too hot. This is the external bypass I purchased: https://www.summitracing.com/parts/prm-1074

This one operates at 180F. The recommended is 140-149F or so from Mazda... hmm.

I agree, the oil cooler is amazing. I had it on since last summer with no issues (Except for the worry of over cooling, but I'm convinced It's not an issue now in the summer time). It's hugh and weights much less than OEM, plus the extra cooling it boasts.
Few more pics of now I mounted it. Im happy with the look of it in the air dam.

The OEM one begins to open at 140-149F, then is fully opened at 180F.

The one I bought begins to open at 160F, then is fully open at 180F.

I did a lot of research before buying it and I noticed most externals oil cooler bypasses open at 180F fully. Even this one that is recommended by Mazdatrix. It just a kinda of hassle mounting the bypass due to how short the oil cooler lines are.

Cart Price Check Part:A0T2-3

That makes sense. I understand now.
I'm still going to keep it as is. I also modded my oil pressure to increase it up to about 80~ PSI.

I'm looking into getting a retro looking oil temp guage and plug it into the old sub-zero plug on the oil pan.

On second thought, I will get an external oil cooler bypass valve after all. Install it some time over the winter. Apparently It's a good idea to have one being that you never want to over cool or waste time heating up the oil. You could potentially do damage to the engine rotors.

The factory oil system has an oil cooler thermstat closed below 60C and also the oil cooling jets for the rotors below 60C (the eccentric shaft thermal pellet). I personally don't see a benefit to eliminating either of those systems. I know a lot of people get rid of the eshaft thermal pellet because they are worried about it failing, but new ones are available from the dealer and they're not that expensive.

Sorry to revive an old thread!

I just bought a '99 spec RB with a single oil cooler, and of course am looking to add another.

My understanding is that the hardlines for the second cooler aren't on the car, so I'd either need to source a set, or plumb it in myself (probably just using braided lines.)

My questions:
1) What length of hose do I need?
2) What is the fitting on the OEM oil cooler (AN10?)
3) What would a plumbing diagram look like -- in series like the original, with a thermostat on each cooler? In a dual cooler setup, does the oil return go back into the same hole as in as single cooler setup? (I can't see why not)
4) How did you mount the second cooler? If buying parts piecemeal (i.e. not a set), what kind of brackets are needed?
5) Anything else I need to know??

Thank you!!

Dig around a little bit, there's a number of threads on adding a second oil cooler. You can either go with a complete turn key upgraded kit like Sakebomb Garage makes, get parts off a R package car to swap to the factory dual oil cooler setup, or add a second one with your own homemade lines and brackets.

DIY is harder than it looks, this is a critical part of your car and if a poorly constructed line blows you will dump the whole contents of your oil pan VERY quickly.

Dale

Good information in this thread! Brings up some questions in regards to what temp oil thermostat to use in aftermarket setups?


Anyone have logs of oil temp going into and out of the engine? Ideally we want oil to hit over 212f to boil off any moisture, thus with two giant aftermarket coolers and copying the factory thermostat with it beginning to open at 150f, does the oil get hot enough?

How to pick the right thermostat, for example here is improved racing's options:

https://cimg5.ibsrv.net/gimg/www.rx7...b5f8c8e80d.png

Here you go Oil Cooler Parts (93+ RX-7)

Thanks, that's a great list!!

Do you guys know if the "how to" is the same on a '99 spec (Series 8/Gen 5) compared to a US spec car?

i.e. do the PS pump and AC compressor still need to be removed in order to add a second cooler to a single cooler car on a '99+?

I found there are quite a few write ups on this for US spec cars...
Triple-R: Crooked Willow Racing Dual Oil Cooler Kit Installation
Oil Cooler
(and also Oil Cooler Installation)