Yeah, I said it.

This just seems like one of those mods where people have been doing it for so long that nobody can really remember why anymore. Is it that important to save $50? You can't even fill your tank with $50 now.

For those of you who have a fuzzy awareness of this mod, basically you delete the thermostat for the rotor cooling jets. It's typically performed during an engine rebuild or A rotary engine has cooling jets that spray oil into the back of the rotor, just like a piston engine with spray cooling jets.



The thermostat was introduced on 2nd generation Rx-7s. Its benefits include:

1) faster time for the vehicle to reach operating temperature, so you can have fun and enjoy driving sooner (rather than driving it very easy while its still cold).

2) faster time for the vehicle to reach operating temperature so you don't freeze your *** off in the winter so much while you wait for heat.

3) improved fuel consumption because less time is spent in a cold condition where the engine consumes more fuel

4) possibly reduced oil dilution because less time is spent in a cold condition where poorly-atomized fuel can end up in the crankcase

Yes they can fail. Any thermostat can fail, but I can't say there's a high rate of failure on original engines. This is probably a harsh thing to say (maybe even uncalled-for), but: Leave it to a rotary guy to take out a thermostat because everybody else told him too, because he's too lazy/cheap to buy another one, or because he doesn't fully understand its purpose.

Did you know that Audi uses computer-controlled oil spray jet thermostat on its twin turbo V8 now?



Now I'm sure that'll cost a gazillion dollars to fix. But a new eshaft thermostat for your rotary is like $50. Think about it on your next engine build.

 

"but but but but...... its another failure point and can cause low oil pressure!!!!"

said someone, somewhere

 

I always thought it was a BS mod as well. There are a few mods like this that rotary guys seem to love.

Worried about temps? Don't go front mount, lol.

I laugh at modded cars listing "delete" options like AC, PS, ABS,etc. Most of the time the owners just don't have the time or money to keep them working. Delete the cheap brake pads, low budget tires and bad suspension bushings, it will drive so much better.

 

Down here is South Florida we DON"T care about warming up our FD's in the Winter..... We won't freeze our ASSES waiting for the car to warm up...

 

We did a rebuild on a 210,000km 13B-REW. Guess which part still worked fine and didnt need replacing? The thermal wax pellet. Put it in boiling water and it still activated to the correct length. They are not as "unreliable" as people say.
And Arghx's reasoning for keeping them in the engine should make this a real no-brainer.

 

You are still going to decease oil pressure/flow on the rotor bearings and front stack when the engine is below 140 f with the stock piece in place. That will lead to more wear.

 

But is it really a problem though?

Because the engine is cool, it should only be operated at low load and rpm, I really do not see how it will make much difference when the combustion chamber pressures are low at that time.

 

In my opinion it is. You see a lot of bearing wear on the main bearings on these engines, especially the rear( flywheel hanging off the end). Most of it is dry starts, and the 1st few seconds of run time.

 

Well... I've got a brand new oil bypass pellet (that came out of my new engine from Malloy) which I'd be willing to sell the people who like to keep them... If ya want

 

The pellet mod increases overall oil pressure even when hot. It also gets to max pressure sooner. It is not just to have oil pressure when cold. I actually tested this on a car that had a separate oil pressure gauge. Both the owner and I noticed the increase in oil pressure after the build. Nothing oil related was changed on the car aside from the pellet delete. It was just an apex seal and spring, and porting rebuild. The oil I put in for breakin was only Castrol 10W-30 as well.

On a side note, I think my engine heats up pretty fast in negative temps but then again I have a 1,100-1,200 RPM idle and I don't wait for it to warm up. I start the car, give it 10 seconds or so and off I go. It hits 80 degrees by the time I get to the highway which is like 5 minutes.

thewird

 

I just made this thread to stir the pot a little bit and take a break from the normal discussion topics.

The first engine in the vehicle usually lasts the longest of all of them, and those had the thermal pellet. There are legitimate applications for deleting the thermal pellet. But most people will blow their motor from something dumb like an overboost when the weather changes. It's not death by rotor bearing wear. Removing the oil jet thermostat results in more "rotary engine hassles" -- often unnecessary inconveniences from driving a rotary engine, like

1) puttering around for 20 minutes shivering while you wait for the heat to come up. Even Florida and Arizona get below 60 degrees outside.

2) driving very easy or half your trip because you don't want to beat on a cold engine (even worse if you get one of those colder thermostats)

3) changing the oil every 1500-2000 miles in part because you are spraying fuel into a cold engine for so long

3) explaining to a passenger that your tailpipe smells terrible because it takes forever to warm up so the mixture has to stay rich

So I guess take your pick... eliminate a very very very minor risk of a brand new thermostat failing, and maybe under some circumstances reduce bearing wear, OR drive a little more "normal" car.

I don't know about you, but after a while on a street car I stop thinking about my rotor bearings and start thinking about enjoying all aspects of the driving experience.

 

If you want to keep it, fine. And I wouldn't recommend someone jack with it on an otherwise properly running engine. But it DID increase my oil pressure across the board on my engine. And it was free. Order up an engine stand adaptor from Adkins and they throw a plug in for nothing. Buy one by itself and it's still cheaper than table salt. And way cheaper than a replacement thermopellet. Where's the downside if you do it during a rebuild? Why not?

 

i will raise you your spot sample.. to my several ---







i took measurements also at max stroke..( on those that still operated ) they all arent the same ... hardly confidence inspiring
... and me for one sticks hands up for a front stat gear bearing fail . 10w-40 oil and a stuck in bypass pellet on a 40 C day = very low oil pressure at idle

i for one make the pellet delete on all FC engines i build mandatory..
the evidence is clear to me ,, if a failed pellet causes ONE rebuild it is too many

 

I certainly agree, most engine wear occurs at initial start up.

That's why I use a 5w-40 motor oil; for cold pumpability, makes oil pressure just a bit faster. It is beyond me why people use 20w-50 oils and some even use heavier.

To me, with all of the modifications people make to these cars that generally make them less streetable, this oil pellet mod is close to the bottom of the list of things that will make the car less streetable, so IMO delete it if you want, keep it if you want.

 

 

Personally, I've removed it for my track FD for higher oil pressures and to eliminate the possibility of it not working. For a street FD, not sure if it matters to remove it...probably helps with getting temps up quickly for emission reasons too much like the pre-cat.

One thing I do to help cold start up is crank the motor a few times to get the oil moving before I fire her up. I use Valvoline VR1 20W-50 or straight 50W oil since it was noted in the thread below that fuel dilution breaks down the viscosity pretty quickly, especially in the hot Cali deserts where I track.

Thread---> https://www.rx7club.com/3rd-generati...thread-872865/

 

how would you cut oil flow to the rotor bearings? they are fed through the irons not the e-shaft..

i can somewhat agree with thrust bearing wear but the engines that had excessive thrust bearing wear had well over 100k miles and most were probably city miles while riding the clutch. look at FC thrust bearings, they all wear on the inside surface due to the push type clutch. FDs have even less problem due to the 50% additional surface but wear on the outer surface due to the pull type clutch.

thicker oil prevents more thrust bearing wear as well as bearing wear upon initial startup. thinner oil will run out of the bearings while the engine is sitting, thicker oil will be retained in the bearing cage and provide some lubrication.

 

The pellet has two modes.
(1) Cold or open mode. It dumps oil back into the oil pan. This also lowers the oil pressure when you need it for cold starts to protect all bearings. This along with the oil cooling jets spring loaded ball valves, prevents oil spraying inside the rotors. How much heat is actually transferred between the rotors and the side housings?. We are told this is to increase side housing and rotor housing warm up which is then transferred to the coolant.

(2) Hot or closed mode. No oil is dumped into the pan and the oil cooling jets cool the rotors with oil that was cooled by the oil coolers.

But if the mod is done, the oil sprays the rotors when still cold. But this oil does not go through the oil coolers. They also have a thermostat to prevent cooling the oil until it heats up.

The question is how much does this actually affect warm up time? We all know that Mazda did some stupid things with this car that any mechanic would know better than to do.
The FPR solenoid is a useless piece of crap that is not needed, and Mazda's description is not logical. I prefer this non stock mode as both water and oil heat up together for a more even warm up instead of only doing the water. We are advised to not use the racing valveless oil cooling jets because at idle, oil pressure will be too low.
With the cleanedup oil pump cavity mods, in summer with fully warmed up oil and the racing jets, oil presssure is still 40psi. One friend used the stock jets with the valves removed and with the resulting larger oil jet size, his idle pressure was also stock. DOH Mazda you got it wrong again.

Since most of us have modded engines, engine reliability is up-most, **** the emissions!

 

its another bypass back to the sump.. one that is temperature controlled,, independent of the pressure control valve
- hot day, thin oil .. front stat bearing is the far end of the queue in a system that is certainly no ring main

hmm

suggest a prudent comparison ..
get the garden hose and sprinkler out , tee it into two parallel lines with two sprinklers on each
set the tap at one setting, observe pattern and distribution,, usually fairly even
now uncap the end of one of the hoses .............. do you expect the furthest sprinkler on the other leg to remain unchanged in flow?

this sprinkler in question is in effect the front stat bearing ... the crank is also turning significantly FASTER than the rotor bearings

at a glance it is pretty obvious to see which plain bearing is most at risk .. however as pointed out above , sometimes its also the rear bearing,, as traditionally these have always proven tight in fresh cranks and new bearings
- as such rx8 crank now has a taper inbuilt on the journal as factory acknowledgement of that issue


PS
as pointed out above,,, rx4- FB 13b and all 12a engines are all happy without the pellet ,, and most stuff post 76 has a thermo bypass in the oil cooler that does the job of speeding up the oil temperature rise

 

just to throw in the curve ball--
of course,,, there is exceptions.. here with have a US 1971 rx2 TD 'cold proof' engine plate
( i stole the pic off ausrotary .. shame on me )

note the unusual oil system routing
this one appears to have a cross connection from the pump output up to the front stat,, making a ring main system ,, i expect the bypass is either blanked or has a control pill to stop or control the amount of oil bypassing the oil cooler via this link

keen eyes will spot an extra relief valve .. obvious conjecture is that this will be a thermovalve to aid in accelerated engine warm up in those frigid climate countries




so,, mazda DID try a thermovalve bypass at some stage
... this one clearly has the disadvantage of dropping system flow everywhere.. it is not a feature on normal market engines.. possibly for that oil system liability reason
- as its not necessary for any reason but AWS

-

 

that is a rather unusual plate, i have 2 almost identical sitting right here but neither have that crossover or bypass on the front iron.