Pat - Never experienced the stock engine having a 4FB1 Diesel under the hood. My bike has high air bleeds on it and if air bound no coolant flows and the high mounted temperature gauge registers low due to the air pocket although the engine is overheating. Probably wise of Fiat putting the fan switch in the bottom of the radiator to prevent it from getting air bound and reading low.

the fan on my 79 will not come on. The fan is good. I have power to the switch. Ive replaced the switch at the bottom of the radiator. The system is full of coolant it would appear. The thermostat appears to be working. i get power to yhe switch but no power out of the switch. Its apparently not getting hot enough to switch power on. Im lost. Out of ideas. Any suggestions.?

Is the car actually overheating? If the bottom of the radiator is getting hot (like 100C) then sounds like a dodgy switch. If the radiator is cool / not heating up much - I'd check the cooling system is bled of air.

A

reep71 wrote:the fan on my 79 will not come on. The fan is good. I have power to the switch. Ive replaced the switch at the bottom of the radiator. The system is full of coolant it would appear. The thermostat appears to be working. i get power to yhe switch but no power out of the switch. Its apparently not getting hot enough to switch power on. Im lost. Out of ideas. Any suggestions.?

Don't guess is my best advice. Get a Laser thermometer and take readings to see exactly how hot the radiator and engine is getting and verify if either is actually getting hot enough to trigger the fan switch. Then go through and dot all the i's and cross the t's so to speak as to air having been bled from the system and such. Remember that if it is actually overheating there is still a remote possibility that a hose is collapsing or that the impeller has come loose from the water pump or mostly rotted off.

Your situation, as you have described the symptoms, and the checks that have been done, seems to be almost always caused by an air pocket in the radiator. Bleed it really well. I like to jack WAY up the front of the car and get the fitting in the head T really high, and don't forget the throttle plate heater tubes if you have one fitted.

.... And as you can see from the threads linked above - a common "customization" is to drill a small hole in the thermostat frame to prevent an air bubble forming there whilst filling.

+1 on jacking the front very high - it just seems to work! (Make sure back wheels are chocked!)

Thanks to all who responded. The car, according to the thermostst on the dash, heats up to about 200f. I dont think the rsdiator is getting that hot. I will try those suggestions and see if they help. Wherever the problem lies, i just dont think the switch is getting hot enough to engage. thanks again to all.

Preserver! The cooling system on these spiders really is very effective when working properly. (Eg it sits around 95C in 100F weather quite easily). "Burping" out excess air is a skill you learn!!

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I have a similar problem. I have a 1971 Fiat 124. One of my mechanics use 'stop a leak' on my radiator. I just unstopped the golf ball size clog at the thermostat. Replaced the fan switch and the thermostat. I am waiting till I can afford a new radiator to flush the system. I ride quit a distance to work and by the time I get to work there is steam coming out of the hood. The fan never comes on. I rigged a switch to the battery and even with the switch on, the fan cuts off the minute I turn on the car regardless if the car is cold or hot. Why is the fan not coming on when the car is running.

Part of the reason I am getting a new radiator is a previous owner updated the radiator with a neck that cap and does not go to overflow. I am worried about doing damage to the engine

Thanks in advance

Changed the switch and fan now comes on and every thing is good....for now. Next!