Radiator fan always on. Strange temp readings.

[moldy]

hi guys, i'm new to this forum. have tried searching for the answer to my problem, but no luck finding it. sorry if this is an easy answer. i have a 79 honda civic which has a couple of issues, and i'm not sure if they are all related or not.

Here are the symptoms:
1. the electric radiator fan is always on whenever the ignition is on
2. i seem to be using a bit extra coolant lately
3. the dashboard temp sensor is not accurate. when the heater setting is set to 'cold' the sensor bottoms out, but when the internal heater is set to 'hot' the sensor sits slightly above the top of the 'normal' range.

If anybody could tell me whether the symptoms are related and what i could do to solve the problem i would really appreciate it.

Regards, Moldy.

[ECU-MAN]

make sure no one has bridged the thermo fan temp sensor wires, or the sensor could be faulty.

Its been a while, But I think the sensor is bolted to the bottom radiator tank.

[heist]

check the earth wires, i had a prob wioth my car, it would "overheat" but its just the tranny earth not done up tight and jigling around...

[EuroDude]

Check for Coolant leaks around the hoses and under the engine. Have you tried another Thermistat?

[dsp26]

myy vote goes to everyones advice here for this matter.

definately check your thermostat too.... go take it out and boil it on the stove... if its stuck open then i'd check for split hoses too if your coolant doesn't overflow through the reservoir.

[Paul1985]

You could pressure test the system to check for leaks if you have access to a tested.
Also, have you checked the thermo switch relay with a multimeter?
If this is faulty it can cause your fan to always be on.

Just a couple of little things you can check, it may not be the problem but definately worth looking at, especially the relay. All you need is a multimeter to check that the switch is working.

[moldy]

Thanks Guys

First check is the thermostat and the switch. I have a Haynes manual, and both seem reletively easy once i drain the coolant.

would any of these symptoms account for the strange temp readings or the extra use of coolant. for example if the thermostat was always open, would this use more coolant which inturn would lower the real reading on the temp guage.

I apologise if this is a dumb question, but as you can tell, I;m pretty new to this. Hoping that the coolant is not related to a head gasket etc. Is this what is checked with a pressure test?

Regards, Richard.

[Paul1985]

with a pressure test you remove the radiator cap and hook the tester upto where you removed your cap. You then pump it upto 15-25% more in pressure than your system holds (check manual or some caps). The problem is you need a pressure tester. If on the gauge your pressure drops (leave it hooked up for a while to ensure there are no leaks), then there is a leak somewhere. This could be either internal (block etc) or external (hoses etc).
If there is no pressure drop then you shouldnt be losing coolant.

If the thermostat was left open then some your car would be slow to heat up initially. Does the car overheat at all?? If you remove the thermostat completely i know it would overheat as too much coolant is going through the radiator and not being able to be cooled in time. I dont think the thermostat sounds like your problem myself... Maybe worth putting a new one in anyways as they shouldnt be too expensive.

Do you know how to check if its opening at the correct temperature?

You definately should check the switch (relay) as this may be the reason the fan is on as soon as you switch your ignition on, it most likely is the reason IMO. Also be sure to check what ECU-MAN mentioned. He knows his hondas!!

I dont know if ive helped at all?? i hope so.

If you have done a headgasket i think it would be pretty obvious. If you are losing your coolant it could quiet be a headgasket??
If it is you should check your system for stray current, you may have a bad earth somewhere which is causing electrolysis in your cooling system. This is bad! I seen a block which had holes right through into the bore from this.

You can get testers for this and its also easy to do with a multimeter, you just need some sort of connection i think (you can make your own somehow but im not electronics whiz). All you need to do is remove the rad cap and then have the car running whilst using as much power as possible.. turn on your hazards, radio, AC, headlights, interior light etc. Now with the tool/multimeter (make sure its on the correct setting for multimeter) place the negative on the negative battery terminal and the positive in the coolant inside the radiator where you removed the cap, make sure you dont touch the sides of the radiator with it or it will give a false reading. Now, a good amount of charge to see is 0.06v. If it is much more than this then you have a bad earth somewhere, most likely a headlight. Make sure everything is grounded properly on your car.

Sorry if ive gone off topic, but its something that you could also check whilst fixing your cooling system.

[Jomsy]

all i did on my `78 civic was flush the cooling system and remove and clean the temp sensor, it was covered in 28 years worth of crap

[Professional]

If you really don't know, better to find professional to do it.

[bigjo5]

switch!!!!

[moldy]

Thank you to every one who has offered their help. looks like my best bet is to test the thermo and the switch. my manual has fairly detailed instructions on how to do both these. are these the type of thing i get get at Repco or similar if need replacing?

Thanks Paul1985 for explaining the pressure test. This is something that i'll have to get the mechanic to do, as i dont have the equipment.

I guess I could get the mechanic to do it all as Professional suggested, but then how would I ever learn. I'm enjoying learning what's under the hood of my little Civvy.