tlniec

Hello,
I've got a 2005 AT, just purchased last month, and I love it! I just have a quick question -- it's been hot outside lately, and I've noticed that in stop-and-go traffic or when sitting at idle (in both cases, with the A/C running), the radiator fan cycles on and off a lot. It kicks on for about 10 seconds or so, then off for maybe 30 seconds, then back on again for another 10... I guess I would normally expect the fan cycles to be longer than that (on the order of minutes versus seconds). Is this a normal RX-8 quirk, or should I be worried? Thanks!

roonsrx

mine is a 2004 m/t and does the same thing, at least you know it is coming on, always watch the temp guage, if it moves much shut the car off. Rotaries hate heat

tlniec

Great, just wanted to make sure nothing unusual was going on. Thanks!

KYLiquid

thats a good sign it means that the car is just steping over what is 'normal' for operating temps and a short burst of the fans is getting it back into its 'optimum' range....thats a sign that the rx8's cooling system, and your personal cars cooling system is in good working order and isnt having any problems with the heat your driving the car in.

I would be more concerned if the fans were coming on and running for a long time then turning off.....meaning that 1) its WAY to hot outside for the car (and that does happen) or 2) the cooling system is getting close to being over-whelmed with the heat and might not be up to the task of keeping the car cool.

What sort of amb temps are you driving in, on a daily basis? Here in FL its been in the 93-95 range most days, add in the heat index and temps near the surface of the black asphalt roads can get well into the hundreds.....even then, in stop and go traffic with the AC on, my fans come on for about 30 secs ever 2 mins or so.

tlniec

Afternoon temps were around 85-90°F on the days I noticed the short-cycling. It has since cooled off -- yesterday evening it was about 70°F and I didn't hear the fan come on at all during my drive home from work.
Now that I think about it, it does make sense that a thermostatically-controlled fan would ideally run in short bursts (maintaining a tight control on coolant temps).

KeithL

Don't mean to hijack the thread, but, has anyone noticed that the fans tend to run longer (and on 'high') after you shut off the car if you've been using your a/c? Of course the a/c generates more heat, but, on my way home, I have a habit of turning off my a/c about a block away from my house, and I've noticed that on days where the temperatures have been similar (in the 90's) the fan runs for a short while on low - if I've turned the a/c off as described. If I forget, and leave the a/c on 'til I shut down the car, the fan positively wails for ten minutes after I shut the car off. I can't imagine that much less than a mile of travel has cooled the engine off that much...?

Anyone understand the logic behind this fan behavior?

Maybe I *should* leave the a/c on 'til I shut down?

(sorry for being long-winded)

KYLiquid

Im not sure how the fans in the RX8 are wired, but in a lot of cars with an electric fan setup you have 2 fans. One is the engine fan, anytime the thermostat reaches XXX temp it will kick on to keep the coolant temps in check. The other fan is the accessory or AC fan, it is set up so it will run when the AC is on if the coolant temp triggers the engine fan on at the same time.

Example : You have fan A (engine) and fan B (AC) when the car starts to over heat, and the AC is off, only fan A will turn on/off to control engine temps. fan B is only operational when the AC is on, it doesnt run all the time, but when the same factor is met (engine temps reach a point that fan A comes on) then fan B will also come on.

So you have 2 fans, they both run when the engine reaches XXX temp, so the 2nd fan copys what the 1st fan does, but only when the AC is on. This is due to the higher air temps over the radiator from the AC and the higher load on the motor to turn the AC compressor.

Like I said, the RX8 might be set up differntly, but thats been my experience with all cars that have a dule electric fan setup.

In my miata, i had it wired up so that the 2nd fan would be tirggered on whenever the 1st fan came on, so that whenever the car reached a higher than normal temp....it would use both fans, regardless of AC being on or off. Even after I deleted the AC from the miata, i kept it wired up like this. Im sure you could do something similar in the RX8, for cool downs bettween runs at the track.

Although all this could be a mute point if the ECU (wich we all know is very smart) can turn on/off both fans whenever it wants, depending on the need.


anyone else know more about the specific setup in the 8

Gomez

This is how the fans used to run. Recent PCM programming may have changed the switch points....I don't know.

Both cooling fans run together. The are controlled by three relays which receive a signal from the PCM. Relay one controls low speed fan operation. If all three relays are engaged, the fans run at high speed.

The fans run at high speed if the coolant temp is 213deg or more, or if the coolant temp is less than 213deg and the A/C is switched on. They'll also run at high speed after the ignition is switched off if the coolant is at high temp or the underhood temp is high.

mikeschaefer

The hotter it is while driving the longer they will run when you shut down. It's because the engine actually gets hotter for the first few minutes right after you shut down. None of the oil is circulating and none of the coolant is circulating, so there is a big dependency on the air cooling to keep the engine from getting too hot.

What I've experimented with and has worked is I will turn the A/C compressor off a minute or 2 just before I get to my parking spot. I'll either run the fan with the semi-cool air still blowing or I'll just open the windows. I'll also let the car idle for about 30-60 seconds before I shut it down. That's usually the amount of time it takes to unbuckle, put away my sunglasses, put my phone in my pocket, etc. Most of the time if I do that then the fans won't kick on after I shut off the car. I' really only have to do it on the 85F+ days though.

KeithL

Gomez, Mike - thanks for the info.

I guess the underhood temp. must be higher when I run the a/c right up until shutdown... I'm just surprised turning it off a few blocks from my house cools the underhood temps down that much (enough not to trip the high speed fan limit)... Like Mike, I kinda figured that this might be cooling the engine off, and, on my old Solara, it was necessary b/c if I didn't, the condenser didn't dry out at all and I got some wicked awful smells the next day when I'd use the a/c... :-(

BTW, just got the heat shield recall (w/ the new flash) done - this part of the fan operation appears to remain the same...