When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I bought my low mileage, very original 93 touring model a couple of months ago. When I got it I cleaned up under the hood and did some other basic work. I replaced the rat's nest (all but a couple I just couldn't get to) disabled the double throttle, flushed the cooling system, upgraded to LS style coils installed on the frame beneath the cruise control, and replaced and added all new ground connections. I also replaced the non functional Bose stereo with an Alpine touch screen, complete with wireless Android Auto and reverse camera, Polk speakers and an Alpine W3 sub with an Alpine 200 watt RMS mono amp with remote sub control. Sounds fantastic! The stock Bose Acoustic Wave is still there in all its glory. I retained all the original parts (even the vacuum hoses) so that the car could, if desired, be restored back to completely original.
But I was struggling on improving the cooling system, my car sounded like it was boiling after any lengthy drive, scary. I bought the Pettit Racing replacement coolant temp sensor, but in spite of their insistence to the contrary it CAN NOT be installed on a car with the air pump (and i live in CA and need to pass smog). Besides, this is not a really good solution as it offers only very limited benefits, so don't waste your money on this. I wanted control of my fans but did not want to replace the stock ECU or cut any wires. So after much research, I came up with a solution that requires no wire cutting, no high voltage wiring and, with the exception of the stock AC fan control (functionality duplicated with my setup), leaves ALL stock fan relays and controls in place and operational. And you cannot see any changes, yet it gives me complete thermostatic control over the 2 primary relays (#1 & 3) which, when activated turn on the fans to 2/3's of max fan speed.
I can adjust the initiating temperature signal from 150 degrees to 210 degrees. I have mine setup so that at 185 degrees the fans run at 1/3 power and at 195 degrees the fans run at 2/3's power. Finally, my fans will stay on after I turn the car off until radiator water temps fall below 195 and 185 degrees. This setup works perfectly, significantly cooler and stable coolant temps and much lower underhood temps, plus is invisible under the hood and can be completely removed if desired to return the car to stock.
Yep, that is it, I read that thread after I bought the thing, looking to see if anyone had figured it out. They told me to drill and tap the housing and I laughed at the idea.
The lesson is, don't believe everything these vendors say. And it took me a week and a half to even get someone on the phone, never again with them for anything.
Good job, the factory fan temperature thresholds are pretty high. How does your setup work, are you interrupting the AC signal wire?
Remember the thermostat will open or close to bypass the radiator depending on coolant temperature also. If you try to cool the car down to 150 degF it's not going to happen without replacing or modifying thermostat. I would be surprised if you can get below 175 degF with a stock thermostat.
I'm using a thermostatically controlled potentiometer (sensor placed in the radiator fins top center), that controls 2 relays that I wired to send a ground signal rather than the traditional power. I depinned the AC triggered ground input on factory relay #1 and substituted one of my relay's ground signals (I trigger that relay from the coolant temp as a default but secondarily from the AC compressor switch to duplicate factory input). On factory relay #3 I added a second ground signal source. This approach retains all factory signals to the fans (save the AC) and serves as a fail safe should my setup fail. I used all high quality components so the likelihood of failure is very low imo, and I tested it pretty exhaustively, works exactly as designed.
As detailed in my OP, I'm not trying to get coolant temps below 175 degrees, that wouldn't be a good idea for various reasons. My settings are 1/3 fan function at 185 degrees and 2/3 fan function at 195. It is possible to adjust these settings within the limits of 150 degrees to 210 degrees but I think my settings are the sweet spots for engine longevity and performance.
It's noteworthy that during my research I found a lot of contradictory and clearly inaccurate information on factory fan control on the forums. I think too much time is spent trying to decipher what the ECU and various sensors are doing and how to control them rather than on the actual mechanism for fan activation. That's why I did so much testing and verification to make sure this approach would work. Ultimately, stable and appropriate coolant temperature is the goal, this does that exactly. And I could, if desired, return everything to completely stock in under an hour, no cut wires, holes drilled or permanent mods of any kind.
Keep in mind that the cooling system is designed to run between a certain range of temps. I forget what that range is on the FD but on one of my old euro cars, you could watch the coolant temp gauge vary between 90-100*C. Turning on the fans during that normal range might not really yield any meaningful results. In fact, more frequent usage of the fans may result in decreased fan life. I burned out 2 oem fans back in the day when everyone would program the fans to turn on really early so attempt to aid cooling. a bit anecdotal but...
To me, it would make the most sense to engage the fans toward the top end of the temp range. Turn the fans on a few degrees past a fully open thermostat. Turn them off at a few degrees below the thermostat opening. I welcome critique of this.
Why did you pick those particular temps in your setup? What benefits have you observed?
Just fyi, I have a fairly thorough grasp of engine coolant system design and functionality. The 13b engine poses unique cooling challenges compared to the conventional piston engines on your euro cars, long story short, they generate far more heat and their ability to dissipate heat is more problematic due to almost constant combustion compared to only 1 of every 4 stroke being combustion in piston engines. To complicate matters, in order to sell the RX7 in America Mazda had to pass increasingly more restrictive emission standards. Part of their "solution" to this was to design in higher operating temps, good for passing emissions, bad for engine life. As model years went by mazda had to backpedal somewhat on this due to unacceptable engine failure rates. Here's an article authored by scotty305 (the poster above) you might find enlightening. https://rotarycarclub.com/rotary_for...read.php?t=646
Since we all want our engines to have long robust lives, keeping our cars running cooler than stock is a reasonable goal. Most aftermarket suppliers recommend a variety of methods to address this need. Many recommend installing lower temperature thermal switches which initiate fan operation earlier. 185 degrees seems to be a well accepted threshold, and, not coincidentally, that's the temperature I picked.
Keep in mind, that the hotter your engine is running the more difficult it becomes to decrease operating temperatures. That's why it's not the best idea to start cooling efforts at the top of the operating range, esp on the 13b. I am not concerned in the slightest about burning up my fans, I am very concerned about burning up my engine.
As far as results, the most promising is the elimination of localized boiling noises after driving the car and noticeably cooler underhood temps both while running and after shutdown based on my infrared thermometer readings.
Thanks for the link. The optimum temps that @scotty305 posted there are helpful references. And reminders. Been ages since I personally have thought about that.
I can confirm that part number PN41-18-840 thermoswitch replaces the original one, I've got that installed in my car. My car still has a few small holes drilled in the thermostat, and I have the ECU triggering the fans at 185 degF and disabling them below 182 degF. That might be a little too cold to work well with an unmodified factory thermostat, the fans might never get the temperature below 185 degF. A higher-pressure radiator cap will help with the boiling/bubbling sound after shutoff, assuming there aren't any leaks in the system. The factory radiator cap for a 2000 Lexus LX470 is the exact same fitment and 16psi which will raise the boiling point by a bit. You can get an aftermarket one from RockAuto (Gates 31336) for under $10.
I'm glad to see people still find those cooling threads from years ago. I posted a similar thread here on rx7club, in case your web browser is unhappy with the security certificate from the rotary car club site: https://www.rx7club.com/3rd-generati...thread-571088/
I know it'll sound odd and controversial but I run little to no pressure (by removing the lower radiator cap seal) in the cars I maintain with good quality straight undiluted Ethylene Glycol based coolant. No boiling over, ever; also no corrosion.
I started with the FD and Evans NPG+ Coolant, and after figuring out that Evans NPG+ is just a mix of 70% Ethylene and 30% Propylene Glycols and proprietary additives I decided to save some $$ and just buy regular undiluted coolants.
This has worked for me great on a variety of engines: 2000 Mazda Protege I4 1.6L 275k miles; 2006 Mazda 5 I4 2.3 L MZR 230k miles; 2009 Infiniti FX50 V8 5.0 125k miles and the FD with 60+k.
That's a really interesting way to approach it, higher boiling point by using more glycol. In theory the glycol should be less efficient heat transfer which might result in hotter engine parts, but in practice it may avoid hot spots since it's less likely to experience localized boiling compared to water.
I'm glad to see people still find those cooling threads from years ago. I posted a similar thread here on rx7club, in case your we browser is unhappy with the security certificate from the rotary car club site: https://www.rx7club.com/3rd-generati...thread-571088/
I 'm aware of this, unfortunately it really didn't give me the cooling capability and adjustability I wanted. From what I read it's a 97 degree switch, that means it initiates only 1/3 fan speed at almost 208 deg F, better than stock but with no ability to configure fan speeds at different coolant temps. It's not super cheap and I read about some having issues installing it. I just did a quick price check and it looks like close to $100 bucks including tax and shipping. The parts for my setup were about $150 and as configured has 2/3 fan speed at 195 deg, I can raise or lower those temps easily. I haven't seen coolant temps exceed 200 degrees, I'm looking forward to seeing my temps on a 100 degree day.
Things like this are why PFC is (was) so popular. OEM integration with the ability to tweak things. Best option for a street used twin turbo build, especially if you’re keeping all smog stuff
01-10-24, 06:43 PM
