Overheating suspect bad ECT
 

Hi all,

I'm a new member in Sydney, I've been maintaing my Mazda Tribute for over 2 years now and its been very reliable only having to do service work and replace a set of sway bar links.

It's a 2005 3.0 V6 A/T

It's done over 300K Km's

A couple of times recently the expansion bottle has overflowed and leaked coolant out normally when driving up prolonged hills (mountains) or sat in heavy traffic.

I've found to avoid this problem you have to have the A/C on constantly to make the fans kick in.

Both fans work as when the A/C is running both fan's operating exactly as they should however, switch the A/C off and sure enough the fan's won't kick in the expansion bottle slowly starts to overflow.

What's odd is the gauge works fine, shows normal warm up and maintains 90 degrees C pretty consistently.

Plugging in to the OBD with IDS doesn't show any logged faults at all and the ECT seems to operate as normal in the live data stream.

I'm assuming the ECT is what triggers the ECU to switch on the fans just for cooling, if there is something else involved does anyone know what else commands the fan to switch on when the engine gets too hot.

If it is just the ECT that triggers the fans does this sound like a problem anyone else has had before? I'm about to order a new ECT and probably change next weekend anyway.

Thanks
Callum

Just wondering how it's going with your repair. I have replaced the ECT sensor on a 2002 Tribute V6 for an overheating problem (not the same as yours). I think the ECT is not your problem, though. You said that you're getting normal gauge behavior and what appears to be accurate live data info from your scanner, so I doubt it's the ECT. I also had gauge and scanner temp info reflecting the suspected accurate temps, but replaced the ECT because I got a new Beck/Arnley ECT for $4.16 as an add-on item with Amazon. Anyway, my fans don't come on until the temp reaches about 213 degrees F. You can use a scanner to see if your fans kick on at that temp. They then go into high speed at around......I'm trying to remember, but it might have been around 220-224 degrees F.

In my case the problem was a new, but faulty thermostat. It was a cheap aftermarket thermostat. I replaced it with a Mazda/Ford thermostat and the overheating problem went away.

I haven't done anything with it yet, because the more I monitor the live data with the scanner I don't think it is the ECT sensor, it seems to behave exactly as you would expect it too.

I sat yesterday in the car park monitoring the data stream it got to around 92degrees C and didnt seem to increase and I got bored waiting. Need more time when I'm not at work.

Out of interest what was yours doing?

My car warms up quick and maintains the temp relatively well (when the fans are spinning) so I don't believe the thermostat is the problem.

As far as I was aware though these cars only had single speed fans. There is an engine self test feature on the scanner that activates the fan and they only spin at one speed.

Our 2002 Tribute V6 has two-speed fans. Slow comes on at 213F. I had to look up the equivalent in degrees C, and that would be about 101C.

I replaced the radiator less than a year ago. Recently, it was overheating and I looked for a leak and found the water pump and degas bottle both leaking and the thermostat tested bad in a pot of boiling water. I replaced all three of those things, but it was still overheating on the freeway going up to 239F with boiling coolant in the degas bottle. The temp gauge would fluctuate between 1/2 up to not quite in the red zone and back and forth. I thought I wasn't bleeding the air out of the system properly, so I got a vacuum fill tool, but it still overheated. I tested for combustion gases in the coolant, but there was none. I suspected the cheap aftermarket thermostat and replaced it with a OE thermostat and now it works fine.

Hi, I just went through my Tribute V6 cooling system wire by wire:
1. Are the fans rotating at 92 degree C? If they are not, please check the relays marked with "cooling fan relay" and "cooling fan relay 1", also check the fan resistor if it is open circuit? the resistor is located at top of the rediator on left hand side. Fuse No.26 is responsible for the power needed.
2. Have your cooling system flushed, the thermostat replaced (actually it should be replaced regularly), use new coolant.

Cliff_Yu, you say your fans come on at 92 degrees C? That is 198F. My Tribute's fans come on at 212.5F, which is about 100/101C. It seems fine that way. At what exact temperature is it supposed to come on?

My own car (2004 Toyota Corolla) has 357K miles (574K kilometers) with the original thermostat, water pump, radiator, and cooling system hoses (ALL cooling system parts are original). I attribute this to regular cooling fluid flushes using the correct coolant and distilled water and NEVER introducing tap water into the system. I live in a hot climate, btw.

I hooked on with OBD reader, and the fan came on 92 degree C with the low speed; high speed came on at ~105. Checked with the wiring diagram, actually the fans have 3 speed, one med speed in between. The slow speed is the power goes to two fans in serial plus one resistor, med speed is the same except did not go through the resistor. High speed, the fans are separately powered by each individual relays.

Another source of coolant loss through the recovery tank is not overheating it is caused by combustion gasses getting into the cooling system usually via a corroded cylinder head coolant passage or a blown head gasket to cooling system passages

Thanks for those tips I wlll check them out this weekend.
1. The fans dont spin at all except for when the A/C is switched on. I will check the relays and also the resistor.
2. That's just good general advice which I will do


I've watched mine with the OBD reader and the fans don't kick in at all. Got to about 107 degrees.

With the A/C running they maintained about 92 degrees. crept to about 95 when I loaded it up with electrical load.

I don't lose any coolant through the expansion tank if I drive with the A/C on. If I switch it off the fan's dont come on, the engine gets hot, then it boils over. I'm sure its not related to a head gasket problem.

So I investigated the fans today, I know the fan motors work because they both come on with a/c.

I tested the three relays in the fusbox they all worked fine.

I then tested the relay that is mounted to the radiator covering.

I didn't get a click from this relay so I assume this is the problem.

I went to two auto stores in my town and neither of them had anything that was right so I've ordered one online