to find out which is bad try the following: after checking for codes …..

The way to test that is to drive it, stop in the driveway and see if the temp climes while sitting - engine running. If the fan turns on it's not the fan or sensor. If it does not jiggle the wire for the fan to see if the harness is bad.

If the fan does not turn on when the temp is high, but does when the a/c is turned on it's most likely the temp sender for the fan.

If the fan is running - no a/c and the temp drops when the engine revs - belt is slipping ( tensioner can go bad - mine did) or the belt is shot and / or the water pump is shot.

 

this is exactly the advice my mechanic told me, which I did today.
when temp was reading somewhere around 185, I put AC on but fan did not come on, but considering how low the temp was, I didnt really expect it too, I just did it to help try and reach operating temps sooner (this was after driving around for 5 mins with heat on to keep t-stat closed longer)
anyways, I turned off AC and left it sit while running, and did a couple things, but stay close. when I went back towards the car, maybe 3 mins later, temp was reading 192 and I heard the fan on, I popped hood and sure enough, fan was running.
so that might rule out temp sensor, but not sure as I didnt think fan was supposed to engage until a higher temp was reached ?

I mentioned this to my mechanic, he said to consider that as a last resort and start with t-stat, but this is exactly what was happening the other night, with heater on high (both heat, fans and all vents open) temp would start to climb, but if I accelerated up to 10 mph faster then coast down, temps would drop considerably.
Im waiting for a call back from the mech as I havent had a chance to explain that part to him.

 

The fan ALWAYS comes on if the AC compressor is on, nothing to do with any temps.

Fan should come on at around 219F and stay on until temp down to about 180F.

T-stat should be close when temp is below 180F and open all other times.

 

FYI. The cooling fan should turn on any time the compressor is engaged. AC or Defrost both engage the compressor. If your fan is not running with the AC on, you either have a problem or the AC control is not truly in AC mode.

 

The water pump is driven by the balance shaft chain, not a belt. If there was a problem with the chain, you would likely be aware of the out-of-balance condition.

If the fan does not turn on with the AC, but does turn on because of coolant temp(but less than 217*... or is it 219*?) this is a strange set of conditions.

 

One thing I don't remember seeing - did you check the actual temperature with a digital temperature gauge. It may just be false readings.. I just ran through that with the wife's Subaru. Dash said hot - car was operating normally. Inferred thermometer said no it was operating normally. Dash gauge sending unit was bad.

My thermostat failed a few years ago - lucky it failed open. I did get a check engine light. Evidently there is a code for the engine not warming up fast enough. I don't remember what it was, but the car ran cold. The stat was a PIA to change.

My fan turns on at 195 and is completely factory stock. Per the inferred thermometer.

I have a very early 2006 ( built in September) car - yes with the oil cooler. Just did the "O" rings....

 

What piece of METAL exposed to air are you pointing your infra-red thermometer at? It is the COOLANT temperature at the sensor that counts.

P0128 will turn the AC off and only rarely cause a CEL. The computer expects the coolant temp to be 180F in about 5 minutes, the exact time and temp are part of a complicate AlGoreithm, not really time but volume of air ingested; so revving the engine has an effect. It is an emissions thing.

 

all good advice, I did think it strange the fan didnt come on, but I didnt really think it would until a certain temp was reached.
my Mazda is like that, if temps are real low, the fan wont come on, even with AC engaged, but it will come on at a lower temp than it normally would.

I am not showing any codes, but I checked it several days ago when this first started happening, not recently, Ill check codes again in the morning, maybe something will come up this time.

firemangeorge, I checked and the AC was blowing cold air, def cooler than outside temps. not saying your not onto something though, I will have the mechanic check into everything posted.
for now though, Ive parked it, Ill start it every few days, but I dont plan on driving it. not until I get this situation resolved.
it certainly is a head scratcher for me, Ive dealt with all sorts of cooling issues over the years and can usually figure it out myself, but I am truly confused by this one, especially after hearing the fan should have come on with AC on.
also with it coming on at such a low temp according to both dash gauges, but I assume they both work off the same sensor so it isnt a surprise they would match.

 

You might check fan relay #50 it may be intermittently failing.

 

spoke to mechanic today, we are going to start at the t-stat and temp sensor, he believes it is/was a block or restriction in the cooling lines. but he hasnt ruled out waterpump, just wants to start at the lowest cost for me and go from there.
so Ill be ordering both those parts today, once they come in, Ill most likely install them myself as it isnt real difficult to do.