Help! Car is overheating, but only 1 fan kicks on

[Taco Cat]

Hey guys,

I am in need of some help! I was driving home from work and noticed a bunch of steam coming from my engine bay. I saw that the temp gauge was maxed out so I quickly got it parked somewhere to let it cool off. The coolant in the reservoir was boiling like mad and there was coolant everywhere, due to my reservoir being cracked. I let it cool for about 30 mins and drove it back home (2 miles) with the temp gauge at normal until I was directly in front of my house. I decided to see if my fans were on so I turned on the AC. Only the main (driver's side) fan turned on, the passenger fan did not turn on at all. I thought this fan turns on with the AC? My AC was not blowing cold at all and usually does within a few seconds. I let it run for a couple minutes like this and the fan never turned on. What's the best way of testing the fan? Could my thermostat cause the fan to not turn on? Any help is appreciated.

 

[Maxx Mazda]

First check the fuses and relays. My bet would be the A/C fuse because the car wasn't getting cold either. Now for the overheating, it could be any number of things.

 

[Taco Cat]

Well I replaced the AC relay and now the AC fan works and the AC gets cold so I fixed that issue. I also did a coolant flush and replaced the thermostat, but now I'm noticing the main radiator fan doesn't kick on unless I turn the hvac knob in the cabin.
Does the main fan only kick on when the car gets too hot? I let it run and get up to operating temp and had it run for about 10 mins after that, the car never overheated. I don't remember if that fan would come on by itself before. Is this normal?

 

[Maxx Mazda]

It's controlled by the ECU when the coolant reaches a preset temperature.

 

[T-Rash]

How are you running now? I overheated at lunch today. Let the car cool off, topped off the radiator fluid, and got it back to my work. Noticed the rad fan wasnt kicking on, so checked the relay. I jiggled it a bit and got the fan going. Let the engine idle for 10 mins with temp at normal. Havnt had a chance to run the car yet.

 

[MrGiggles]

The fan is supposed to switch on at 205* and shut off at 199*F. This can be monitored pretty easily if you have a scanner or a bluetooth ELM327 adapter and the Torque app. The drivers side fan is the one that primarily controls engine temperature.

The PCM shuts the A/C down when the engine is overheating. I don't know what the specific cutoff temp is though.

 

[P-Funk!]

If jiggling the relay caused the fan to turn on - replace the relay.

 

[Taco Cat]

T-Rash- I'm running fine now. I'm guessing it was just my thermostat stuck closed that caused it to overheat, which according to MrGiggles causes the AC to shut off so that makes sense. I'd replace that relay though, like P-Funk! said. Might be worth replacing the thermostat and doing a flush if you have the $$ and time?

MrGiggles- Thanks for the info! Nice to know that the AC shutting down is normal when the engine overheats. I replaced the relay anyways since I got it for $1 at the junkyard. I'm also thinking about getting one of the bluetooth OBDII readers. They sound really useful!

 

[T-Rash]

New t-stat will be here in the am. I'll replace that, flush and replace relay. Thanks! I replaced the water pump a couple years ago when the timing belt was updated, so Im hoping it is the thermostat thats being a b****...

 

[LostinCanada]

@Taco Cat... I'm using this bluetooth reader, plugged in 24/7 paired with the Torque app (Pro) - need an android device for this setup though. It's highly customizable and awesome for monitoring, testing, checking/testing OBDII codes etc. Is the 757 in your location the Boeing variety? I fly also...

 

[pcb]

If jiggling the relay caused the fan to turn on - replace the relay.

Check the connector the relay plugs into as well...
Look for corrosion, dirt, or bent pins that can cause a bad connection.

 

[T-Rash]

Check the connector the relay plugs into as well...
Look for corrosion, dirt, or bent pins that can cause a bad connection.

I think it just so happened to kick on once I started jiggling. The relay looked clean and not corroded or bent up. I replaced the thermostat, topped of rad fluid and hit the road. Temp is holding at normal.