Fan Won't Come On

[courtenay]

Thanks, Jim. Now I have a spare. I don't think the sensor is the problem. I think it is the gauge - Chris is sending me one of his spares. The thermostat is stuck in the open position, which I think should result in the engine running cooler rather than hotter. I've ordered a new one anyway. I'm also going to install one of Mark's variable temp sensors that will take the radiator sensor and the gauge right out of the equation.
Finally, all else failing, I've got the manual switch you installed as fail safe.
Cheers,
Bruce

[courtenay]

So - finally got the new t-stat. Three weeks to get from Texas to Vancouver Island. We Canucks really have to plan ahead when ordering parts!! Damn Canadian Customs!
Anyway - installed the t-stat, burped the system and let her run. Same thing. Fan didn't come on 'til the temp needle was just below red zone. Swaped gauges with the one Chris sent me - same story.
I did use an laser temp probe to check the rad temp. At the point the fan came on, the temp was pretty consistent top to bottom - about 200 deg F. All hoses were also fairly consistent temp - again around 200 deg. The only part that was warmer, was the the side of the tstat closest to the water pump - about 240 deg. The engine block temp varied - again in the 200 deg range.
So, I'm at a bit of a loss here. I don't think the thing is actually running too hot - but I can't explain the gauge readings.
Any thoughts???

[jimmycakes401]

Wow. This was a good thread until it just stopped... LOL

[courtenay]

I think it was picked up on another thread. Anyway, the problem turned out to be the temperature sender in the block that "spikes" the needle on the gauge. On my '80 Fi, there are two senders in the centre of the engine block. The one closest to the firewall is the one that sends the actual temperature to the gauge. The one closest to the radiator "pegs" or "spikes" the needle. If the car had an idiot light to indicate an overheating condition, this is the sensor that would turn the light on. I don't know the technical details on how it works, but several other folks on the forum suggested that it could be disconnected without doing any harm as long as the other sensor was working. I disconnected this sensor and problem solved! The gauge rarely goes over 190 and the fan comes on at about 190. I have a replacement sensor but have not installed it yet. The old one remains in the block but is not connected.

[jimmycakes401]

Decided to pull the stat and drill a hole like everyone recommends... well... my stat doesn't look like the ones I see in the photos. Did the 1981 not have this problem? Here's my stat

[jimmycakes401]

I figured it out. Thought I was looking for a valve or a flap to drill through. Found this blog:
http://handbuilt-by-robots.blogspot.com ... epair.html

I drilled just under an 1/8" hole. Sound good? Boiling it now to test it.

[jimmycakes401]

Everything is working perfect now. Fan comes on and everything! Found an acorn in there as well...
http://fiatspider.weebly.com/1/post/201 ... -heat.html

[DRHSMITH]

i actually still have this sisue i believe its the temp sensor but i took ones form 2 other aprts carrs did nothiong s i got and extra double female plug lead about 1 ft long and just directly plug the round side in to the terminals in the hood cavity on hot days lol

[jimmycakes401]

Try cleaning every single connector. Unplug them all and give them a good brushing. The connector to the fan was a little oxidized and made it run on and off. Cleaned it and now there is no problem. Staying at 190 and not going anywhere. My fans a little loud. Are they all a little loud? It's not catching on anything.

[manoa matt]

I would suggest putting everything back to stock and how Fiat wired it, as it's the most reliable.

The temp gauge sending unit in the cylinder head works via resistance. As the temp rises the sending unit increses in electrical resistance. The increased electrical resistance is measured by the dash gauge and corresponds to the movement of the needle. The wiring for the circuit is as follows: Temp gauge sending unit is wired in with the temp gauge sensor that pegs the needle. Both sensors are then wired to a "temperature gauge resistor" which is located up under the dash in what looks like a fuse holder. The wiring then goes to the dash gauge.

The senders and gauge rely on resistance for the reading at the gauge, therefore any additional resistance in the wiring circuit will result in a higher than actual temp reading at the dash gauge. Corrosion at the terminals or hard cracked wiring near the cylinder head sensors will add resistance. To correct the situation and make the gauge read a more accurate reading you need to clean all the electrical contacts in the circuit and replace any wiring that is corroded or exhibits hard cracked insulation. You also need to gently clean the contact surfaces in the temperature gauge resistor. When you open the holder you will see a ceramic core with a tiny copper wire wound around it with caps on each end. You only need to clean the caps at the ends and the corresponding contact points inside the resistor holder. Do not break the copper wire.

Once complete you can verify the results with a non contact laser thermometer. You want to point the laser at the metal cylinder head between the sensors. Its the metal temp you are looking for not the water temp.


The stat in the photos is the OE Savara brand which is an 80 deg. Celcius stat. Most of the current stats being offered are made by Behr and are 90 deg. Celcius.

[RRoller123]

Yeah the fans are a little noisy, compared to modern cars. Mine makes quite a buzzing too. As long as the blades are free spinning, not hitting anything, you are probably ok. Check it cold, those blades could do quite a number on fingers.

[jimmycakes401]

Yeah. I should check my sensors. My wires are all stock with the exception of the connectors that had been ripped off by the PO. I had to re-attach those. I didn't end up cleaning the sensors because all my problems went away. Now to tackle some other issues.