Fan wont come on (radiator)

Neu · Post by **Neu** » Sun Jan 06, 2008 9:43 pm

So yeh, car gets nice and hot when i'm idling it, so my fan isn't coming on (haven't heard it come on in a while).

Anyway, how do I troubleshoot this on a tercel?

takza · Post by **takza** » Mon Jan 07, 2008 6:13 am

On mine...the fan defaulted to RUN...meaning that it wants to run all the time except IF the switch is working.

When my last fan switch went out...it wanted to run too often...when not needed.

You need to drive it to temp...let it sit and idle...WHILE watching the gauge. When the gauge starts to go over the middle mark and the fan doesn't run...then you have a problem?

splatterdog · Post by **splatterdog** » Mon Jan 07, 2008 8:26 am

A real quick check of the fan and power to it is to pull the fan switch connector at the bottom of the rad with ignition on. Fan should come on.

If not and it's an 84 or 83 you might be due for a new fan. The earlier ones are a little different design and might be prone to seizing like mine did 4 years ago. Finally gave up when it was almost 100 degrees out and I was on the other side of town.

Keep your heater going until you figure it out and fix it. It will cool the engine sufficiently in a pinch.

good luck!

Neu · Post by **Neu** » Mon Jan 07, 2008 10:33 am

it's an 85. The car gets to red hot on the temp gauge and it still doesn't turn on. It's snowing out here so there's a lot of sitting around in the car. Anyway, i'll try to find that switch at the bottom of the radiator.

Post by **Petros** » Mon Jan 07, 2008 2:33 pm

That could be a thermostat not opening. the engine gets hot but not the radiator because there is no water circulating through it.

unplug the rad temp sensor to see if the fan can come on, if it does remove the thermostat and test it in a pan of hot water on the stove.

good luck

takza · Post by **takza** » Tue Jan 08, 2008 2:59 am

Neu wrote:it's an 85. The car gets to red hot on the temp gauge and it still doesn't turn on.

Every time it gets hot you shorten the life of the head gasket. I'd just replace the thermostat and try to turn the fan blades to see it it is seized?

Neu · Post by **Neu** » Tue Jan 08, 2008 10:22 am

well i stop it before it usually gets to red hot, anyway, I unplugged the fan, and it hasn't even gotten half way up the temp gauge now. So it isn't the thermostat, cuz that was opening anyway (once I hit high speeds it'd cool down anyway, so i knew it wasn't the the thermostat)

so should I goto a junk yard and grab one of the sensors or just order a new one? For now I'm fine leaving the fan running all the time, I know it'll be hard on it, but I have no money right now.

takza · Post by **takza** » Wed Jan 09, 2008 5:31 am

It'll reduce your mileage some...probably could get a used sensor for next to nothing though.

Neu · Post by **Neu** » Wed Jan 09, 2008 11:31 pm

takza wrote:It'll reduce your mileage some...probably could get a used sensor for next to nothing though.

Really..I wouldn't think it'd reduce my mileage...since I figured all that sensor did was tell the fan when to pop on.

Although yeh...it'll keep the coolant colder for longer, which might lead to worse mileage if I dont allow it to warm up, that I'm not too worried about though. I get 24 mpg though, which isn't too shabby for these cars.

takza · Post by **takza** » Thu Jan 10, 2008 6:04 am

It takes HP (gas) to run the alternator needed to run the fan...and in winter you'd better have good antifreeze protection cause the rad can freeze.

Several people have tested mpg gains just by running their car off the battery with the alt belt off.

Logbear · Post by **Logbear** » Tue Feb 26, 2008 10:22 am

My problem is that the radiator fan runs all the time. If I unplug the wire that plugs into the sensor at the bottom of the radiator, the fan turns off.

Some previous owner had a problem in the fuse box under the hood. The receptacle for the fan relay that plugs in there is broken and it's been rewired to a little black BOSCH relay that is screwed onto the outside of the fuse box. I can unplug wires from the relay and make the fan quit running.

At first I thought the problem was the sensor in the radiator so I took one off another radiator I had and plug that in. The fan still runs all the time.

Can anyone explain the sensor theory to me. I checked continuity between the contacts in the sensor and there is continuity. I thought that when it got hot it would complete the circuit, but that's not the case I guess.

Do I have 2 bad sensors, or was something wired wrong?

xirdneh · Post by **xirdneh** » Tue Feb 26, 2008 11:44 am

[quote="Logbear"]My problem is that the radiator fan runs all the time. If I unplug the wire that plugs into the sensor at the bottom of the radiator, the fan turns off.

quote]

Once I was playing around with the green connector plug that has wires going to the carborator solenoids and choke. Cannot remember the details
but the fan came on and ran non-stop. I put everything back to the way it was and it went back to normal. I wish I could remember what I did. Its a long shot but maybe something to check.

Logbear · Post by **Logbear** » Tue Feb 26, 2008 6:40 pm

Well no luck so far. In fact, now that I've fiddled around with the wires and fan relay, the fan stays on all the time whether the wire is plugged into the radiator or not.

I followed the FSM instructions to check for severed wires with a continuity tester and found that one side of the radiator plug goes to ground and the other side goes to the relay. I think that's the way it should be. I've also been using the wiring diagram but that hasn't helped much.

I also unhooked the wires from the BOSCH relay and plugged them into a relay that came off my other car (fan working normally), using my other car a a guide.

I'm still baffled.

The car with the problem is an "83". The one I'm using as a guide is an "86". Everything looks the same.

Al least the fan does turn. I guess that's better than having it not turn.

Does anyone have any suggestions?

Mac · Post by **Mac** » Tue Feb 26, 2008 7:42 pm

my relay got destroyed (don't ask) so my fan dosn't work at all, overheating is only a problem when the car isn't moving.

takza · Post by **takza** » Wed Feb 27, 2008 3:36 am

I'd say it's a bad sensor....the system defaults to run? The sensor shuts the fan off unless it detects HOT?