to prevent vapor lock and hard starting when the engine is hot.
I have a fj73 and a fj62, but neither have the fan, and they start ok when hot, so I don't know how critical they are.
Although these are both 3f's, and the plastic carb heat shields could be adequate.
I have a 78 FJ40 all stock except the removal of alI smog equipment. I experienced vapor lock today. It was about 90 degrees outside. Running at high speed today my engine was warmer than I have ever seen it. When I came to a steep long hill my engine started bucking and loosing power, I actually shifted down to third. When I got to the top I took it easy, the engine cooled down immediately to its normal running temp and I had full power again. My radiator is about 20 years old. Maybe I will have it flow checked.
It's exactly what they said above. There is a thermistor(thermo switch) on the intake manifold and when it reaches to certain temperature while the engine is operating and then shutoff via the ignition, a circuit board (1979) located under the dash will activate the fan. And there is a relay near it. I believe this circuit works like a timer; anyhow, the thermistor just activates it. Not familiar how other years are setup but still uses the same concept. The exhaust manifold/ engine generates so much heat when engine is off and the carb cannot do what it is designed to do and that is create a vapor like mist and send it down to each piston when the engine is trying to start. Basically the heat threshold in the carb has been exceeded. In some regions if the engine is running correctly ( temperature wise) it will not vapor lock when trying restart the engine. I had one 40 that it was removed by PO and it started every time even in the summer. Toyota has done their homework, they are pretty good when it comes to design in regards to these 40s.
I do not know about starting mine was running. It always starts in hot weather. I was driving about 65 mph, I doubt if the fan clutch was activated at all. I believe the fan clutch works cause it will idle all day at 90 degrees and never get hot. I might be a half quart low on oil but it has 8 1/2 reservoir!
I will be pulling a heavy trailer with mine today. I am throwing my temp gun into the rig so I can get an idea what temp my factory gauge is indicating. I do not know if I have a thermo switch on my manifold or a circuit board up under the dash. It is always very dependable so I work on it very little especially under the dash.
It was only 72 degrees and highway driving pulling a trailer, it got above normal operating temp. I stopped, turned off engine and checked the fan, it was freewheeling. When engine is warm, does the fan clutch lock up? When I then started the engine and revved it up I could feel a good blast of hot air coming from the fan.
Since you have temp gun point it before the thermostat housing and radiator hose. And wait for engine to warm up to point when thermostat should open and see if the upper water hose is the temp as the thermostat housing. Someting to check or at least confirm it is indeed opening.
Yup on the air flow. You can use a small piece of tape on one of the blades to the shroud and cycle the engine on/off see it broke after it was running. The fan clutch should lock up and force the fan to turn when exceed the temp of the fan clutch. I sometimes use a screwdriver to hold fan blade in place while someone else cycles the engine on and then off. This can be dangerous so be careful.
Headers will reduce the underhood temps after shut down compared to the cast iron exhaust manifolds. The carb fan is designed to come on after shut down to make it easier to restart. I don't think they have any effect while driving.
I experienced a pretty severe vapor lock issue out in Eastern Oregon one summer that would show up while driving or after being parked a few minutes. Turns out the bolts holding my fuel pump together had gotten loose and were likely allowing some air into the system at that point. I didn't notice this until after I changed out the pump thinking that the diaphragm had torn. I never remounted the problematic pump but the bolts/screws were definitely loose and I couldn't see any issues with the diaphragm after a closer inspection.
I am going to look at the radiator. It is at least 18 years old. I change antifreeze every four or five years but two years ago my front heater was not working very well so I tanked it out, what an improvement. So maybe my radiator needs some attention. Anyone know of some really nasty radiator cleaner? A home mixture would be OK.
In my opinion it is best to rod it out. A cleaner is ok but if you run good antifreeze and replace it every 2 to 3 years you should be ok. The say the antifreeze properties that keep the oxidizing down will last about that long but the heating and freezing protection properties last longer. Personally I have no clue. Find a good radiator shop and ask them the status of the radiator after they worked on it. I've had some that the radiator was so bad they seal some of ports. Sometimes replacing the radiator is the only option.
Have an old fashioned radiator shop look at it and take his advice. May just need rodding/boiling out, may need a new core, may need a new radiator. If it is a good old shop they will do the least expensive proper repair. Your problem sounds a lot more like radiator/cooling issues than carb cooling fan issues.
Removing the all the radiator hoses and clean the the housing it is attached. Like the thermostat housing will usually bubble up with corrosion. Remove the corrosion and apply grease before installing the hose. Anything that corrodes will require you attention...water pump is another. Just saying.
Has anyone had a problem with the fan circuit shorting after a rain. I never figured it out and just removed the circuit to save the battery. But after a rain the fan/relay would chatter and randomly start blowing.
Removed thermostat, drained out antifreeze, poured some block cleaner in and have been driving it. Soon as you get up to high speed starts overheating. Ordered a new radiator and thermostat . Received the thermostat today. My old thermostat had a rubber gasket on the top of it, the new thermostat did not have a gasket. Is there suppose to be one?