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Discussion Starter · #1 ·
Hey guys, I just got my motor running and I cant seem to get the radiator fan to turn on. I bought this car and tore it apart right away so I dont remember when it would turn on. I pretty much replaced everything from the head up except radiator and fan.

I got the car running a few days ago and the fan wouldnt turn on but it really didnt get to very high temp ran it for about 5 minutes. The car doesnt have any plates so I cant drive it, but I drove it down my street, and left it running for about 20 minutes today. And it wouldnt overheat, but the highest it got to was about the A in NORMAL on the gauge. And the fan still wouldnt turn on? Again not overheating but when should this thing turn on? I also replaced the relay just for good measures.
 

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Umm.. Bump :)

Oddly enough I have the exact same question as well as the same situation. No plates but I can’t get it to heat up enough for the fan to come on.. I have checked the Relay it clicks over and I have hard wired the fan it comes on. But can’t get them to go together yet at least. So anyone know or is there something else we should check?
 

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My fan kicks on at the R, the highest I got the needle to go is to the M and I started to get worried, but then the needle dropped like a rock and sat at N, like usual. Only reason it got that hot is because I had to show a ricer what was what. hah.
 

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This seems to be a MAJOR problem with these cars that everyone is starting to have. Many people seem to say that it's the relays' faults, but that is often not the case. I did the relay rewire on my car and my fan will not turn on by itself when the engine is getting hot. I plan on replacing the coolant sensor in the future to see what that does, but I sort of doubt that is the problem. I am beginning to believe that the problem lies in the computer. I have a hunch that the relays break in the computer and won't turn the fan on when the engine is overheating. If I figure it out, I will let everyone on here know!
 

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Discussion Starter · #5 ·
Yea, thatll help, I am going to replace my coolant sensor tomorrow and see if that helps. I'll also keep everyone updated. I havent changed the actual low speed and high speed relay, buts just the relay in the fuse box under the dash. I have a feeling those relays arent bad though, I know the low speed relay is working.

If the problem is in the computer, how does that happen? How is it fixed, replacing the whole computer?

Also can someone make a diagram of how to wire up the fan manually? Do you just run a wire from the fan motor straight to the battery with a switch and fuse in the middle? Or do you put the switch in the relay wires? If it is the relay wires, high speed? Low speed? What color are the wires?

What if I just buy one of those universal electric fan controllers? I work at advance auto parts and we have a universal one that comes with a sensor you put in the radiator fins, and at a 180* it turns the fan on.
 

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i have the same problem, but im just going to hard wire my fan to a swith. when it gets to a point were i start to worrie flip the switch and fan turns on lol
 

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aftermarket automatic fan switch + stock sensor/relay

if the problem is in the ECU, not the relay or the sensor,
could I leave the stock sensor in place, run wire from the output lead of the stock sensor to the aftermarket automatic fan switch and then to the stock relay?

If I have this right, the problem is in the part of the ECU logic that uses the coolant temp sensor to turn on the fan, not the part that uses the CTS input to control the mixture.

The faulty fan switch logic in the ECU is then bypassed by sending the "HOT COOLANT" signal directly to a switch that then energizes the fan relay. No need to add another sensor (which involves making a hole in the radiator or snaking a line into the upper hose) or rely on the driver knowing about and remembering to use a manual switch when they remember to look at the gauge and see the gauge reading hot.

Or would I be robbing too much current from the stock sensor by using the one sensor to feed the ECU *and* an aftermarket switch?
 

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uh... afaik the cooling fan sensor is just a temp sensor and changes resistance throughout the temp range, when it hits a certain range, it grounds, which makes the connection at the fan relay and kicks it on. Buuutttt.... the 1.9 CVH is different than the 1.8 BP so what do I know? Should be similar though.

When I got my car I thought it was the relays as the fans would not kick on all the time, most times they worked fine. I looked into it farther and the fan temp sensor was actually broken.
 

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doesn't the CTS go to the ECU and then the ECU decides to tu

doesn't the CTS go to the ECU and then the ECU decides to turn on the fan (or in our case, decides *not* to turn on the fan).

I don't have the manuals yet (on the way from Amazon and eBay)

If that's the case, that the current from the CTS could energize the relay, then I wouldn't even need the aftermarket switch, right? just jumper from the CTS directly to the relay. I'll have to look at the schematics when the book arrives to see how much current is in the sensor circuit. I thought sensors run low current, that's why the aftermarket kits include a sensor (very low current to trigger the switch) and a switch (medium current to trigger the relay) and a relay (sending high current to the motor).

silverton said:
temp sensor...changes resistance throughout the temp range, when it hits a certain range, it grounds, which makes the connection at the fan relay and kicks it on. ....
 

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Like I said, when I owned my 1.9's I just drove them into the ground and didn't really work on them much, if at all, so my knowledge of them is very minimal. I KNOW on the 1.8 mazda motor there are three temp senders. One for the fan, one for the coolant gauge and one for the ecu for timing, fuel, etc.
 

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Your 1.8 had a CTS sensor that went directly to the fan relay?

then maybe I can go to the JY and get a 1.8L fan sensor, and wire it directly to my fan relay if there's a boss on the water jacket somewhere to mount the extra sensor.

silverton said:
the 1.8 mazda motor there are three temp senders. One for the fan, one for the coolant gauge and one for the ecu for timing, fuel, etc.
 

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my fan kicks on before the N in normal but thats where the cars temp has always sat since i got it last year is it messed up or working correctly
 
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