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Re: Engine fan power. 73 1608.

Posted: Tue Jul 30, 2019 12:22 pm
by bartigue
If the fan comes on and everything stops then you have a significant enough voltage drop that the battery isn't recovering quickly. The only time I've seen this is on the car I mentioned earlier where the new terminals were painted on the inside. Could be as simple as creating a better ground for the fuel pump. Personally I'd add back the mechanical pump.

Re: Engine fan power. 73 1608.

Posted: Tue Jul 30, 2019 1:31 pm
by zonker
Funcar wrote:
Tue Jul 30, 2019 9:50 am
Zonker. I bought the thermal switch from AR and told them what engine size so know they would have sold me the correct one for this car. I don't have a laser thermometer and may pick one up to run this check. I agree the gage may not indicate the actual temperature near the switch and thus it doesn't activate. As mentioned above the fuel pump gets it power from fuse 10 (L) and it has a 16 amp fuse. The engine fan is wired to fuse 1 (A) and it is also a 16 amp. fuse. It passes through a relay attached to the fender and you can see the wiring in my pictures above of the 5 wires going to it. 1 black, 1 green with a black stripe , 2 violet and the green power wire that goes to the motor of the engine fan.

I bled the coolant system again last night and will test again today.
Since you have a trunk battery and different color wiring, I will guess that your car is a lot more 1975 and a lot less 1973. The two purple wires are the same as what I pointed out earlier however, one of those wires goes to the fusebox A and the other is the main power lead for your horn relay.
The green wire if that is the positive wire and is burnt on the relay connection, you might have a fan motor that is giving up the ghost. That would explain the burnt connector and the occasional blown fuse.

The thermal switch comes in varying temps, it usually has the temperature stamped on the side of the switch itself, like 82C, 87C, 92C, or 95C. I think Fiat's choice of putting the fan switch on the bottom of the radiator is a poor choice, given that the warmest coolant is going be exiting the top hose into the radiator. It seems as if the bottom of the radiator is at 87C (189F), the cylinder head is a good 15 degrees hotter, so in actuality the fan will not kick on until the motor is over 203 degrees. I think that's way too hot, given these cars are not young spring chickens anymore. At the very least, make sure the car has a lower 82C switch so then the radiator fan will engage when the head temp is around 194 degrees.

What I did in order to get the fan to activate sooner is add a 170F coolant fan switch from a Honda motorcycle to the coolant port on the intake manifold where one of the emission switches resided. I ran a single wire and connected it to the black/white wire on the power side of the original cooling fan switch, and now my fan kicks on at 180F and off at 175F, a little lower than ideal but I much rather the fan run a little longer than shorter.

I would add a relay and a rollover switch to the electric pump, and activate the relay off of your current power wire (and put an 8 amp fuse back in that location), main power for the fuel pump should come from the battery with it's own inline fuse. To wire in the rollover switch, add it somewhere on the 85 or 86 wire of the relay and now you're protected in the event of a rollover.

Re: Engine fan power. 73 1608.

Posted: Tue Jul 30, 2019 1:56 pm
by davedecker4
I wouldn't do any of that. Your car is nearly stock, at least for one of those years. Figure what's wrong before attempting any 'improvements'.
You know the fan runs by connecting the wires. You know the switch is good because you got a new one. You know that something was wrong before by the evidence of fire/short/melting in connections and area. First, do not reuse that relay! You know something fried there and they are easily replaceable at parts store, don't create (or recreate) more problems. Replace it along with connector block and cut away or replace any of the wire that's fried. Then check the ground nearby. Clean it up and reattach (it's a Fiat, it's always the ground). Then follow the wire and look for any short, bare spot, burnt spot, etc. Address what you find. This will probably be the cheapest, safest, and quickest way to address this problem so you can get some driving time in before that Canadian fall arrives early, eh.

Re: Engine fan power. 73 1608.

Posted: Thu Aug 01, 2019 7:06 am
by Funcar
You are absolutely right Dave. I intend to fix it correctly. Currently try to source the connector block.

Re: Engine fan power. 73 1608.

Posted: Thu Aug 01, 2019 10:18 pm
by zonker
davedecker4 wrote:
Tue Jul 30, 2019 1:56 pm
I wouldn't do any of that. Your car is nearly stock, at least for one of those years.
Lots of stock 1608cc 1975 models running about?