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.

[EuroDude]

Let us know how it goes :thumbsup:

[moldy]

Well today I replaced both the thermostat and the temp sensor and gave the radiator some new coolant. The car seems to be running ok. i've topped the coolant up a few times.

The temp guage on the dash is now giving more sensible readings, and the radiator fan does not run as soon as i hit the ignition.

Having said that, I have not seen the fan actually running since i did my repairs!! not sure whether it simply hasn't needed it driving around Tassie, or whether i've buggered it. I guess time will tell...

Can anyone give me an indication of when the fan actually should come on? Ive been so long with it on constantly!!!

Thanks to everyone for their help. I now need to watch the coolant level to see if it is using too much, and get that pressure test when next i service it.

[EuroDude]

The fan should come one only when the engine temp exceeds a certain temperature. I guess if its very cold weather and the engine is only idling, then the fan may take a long time to spin.

Give it a few decent revs while you are checking the fan, the temp gauge should overheat if the fan is not working.

[moldy]

EuroDude, will the car overheat without the fan. I.e. will I be able to tell that the fan's not working by the car overheating??

I took the car for a fairly decent run around the city yesterday and left it running in the driveway. The car never overheated, but I didn't see or hear the fan operating. But I guess that's not to say it didn't come on for short periods when needed.

[Mr_will]

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.




your bit about pressure testing was very good, but you arent on the right track with this bit

if you had no thermostat at all (exactly the same as it being stuck open), then coolant is ALWAYS circulating through the radiator, meaning at startup, it will heat up more slowly.

on startup, coolant circulates the block only (assuming the heater is off), and thust warms up more quickly.

once it reaches the magic temp (78degrees on my b18a), the thermostat opens and the coolant now circulates through the block, through the radiator and back.

the engine would not, as you suggested overheat if coolant was circulating the radiator all the time. it would run cooler on startup, take longer to warm up, and lose temp when cruising at freeway speeds (these are the key symptoms of a thermostat that is stuck open)

[Mr_will]

The fan should come one only when the engine temp exceeds a certain temperature. I guess if its very cold weather and the engine is only idling, then the fan may take a long time to spin.

Give it a few decent revs while you are checking the fan, the temp gauge should overheat if the fan is not working.


for the fan to come on, all the coolant in the entire system has to be above the thermostat temp (around 78degrees on my car), as opposed to just the coolant in the block being above this temp for the thermostat to open. it takes quite a long time if you just turn the car on and idle.

drive your car for 15-20 minutes, then when you park it, let it idle for as long as is necessary. one of two things will happen:

1) your fan will come on and you will be happy because it is working

2) temp will creep up and you will turn off your car and figure out why your fan isnt coming on.

[moldy]

I have not yet seen the fan come on, but the car has not yet over heated either. I will take if for a 20 minute drive today and test it as Mr Will said.

Although this morning when i had another quick check (before reading the last post), and while i was watching with the bonnet up to see if the fan came on, i noticed a small amount of steam coming from the radiator cap. is this normal when you have just changed the coolant (possible excess escaping etc) or is it something i should worry about.

I noticed the steam after maybe only ten minutes revving in the driveway. Perhaps it justs liquid caught under the rim of the cap that needs to evaporate??

Again, the car isn't overheating, and never did.

[Mr_will]

its pretty common to get a bit of steam after changing the coolant, you may spill a little here and there and it will heat up and evaporate as you said.

when you changed the coolant, did you remember to flush the block, the heater core , and the radiator? most of the shitty deposits build up in your heater core, as this is where the liquid sits for the longest period of time without movement. it can basically defeat the purpose of changing the coolant if you dont flush the heater core, because the next time you turn the heater on after changing, you put all the crap that is there, back into the system

[aaronng]

I noticed the steam after maybe only ten minutes revving in the driveway. Perhaps it justs liquid caught under the rim of the cap that needs to evaporate??

Again, the car isn't overheating, and never did.
The engine block heats up faster if you drive around rather than by just free revving in the driveway.

[moldy]

I did exactly what Mr Will suggested. Take the car for a long drive, then pull up and let it idle until the fan either comes on or the car overheats. Luckily, the fan did come on!!! Which means I have successfully fixed 2 problems:

1. The fan now only works when required
2. The temp guage on the dash gives more sensible readings (although they still differ depending on whether the internal heater is on or not!)

Having successfully fixed that problem, I am now going to move on to a couple more problems that need attention:

1. My engine has a slow oil leak that I intend to find the cause of.
2. Only one strip on my rear defogger works, and I'm going to fix/replace it.
3. Small rust spots on the body need fixing.

Fingers crossed, and thanks heaps to everyone for your help.

[Mr_will]

glad to hear you figured it out in the end.

keep us posted if you need anymore help :thumbsup:

[moldy]

Thanks mate, I definately will. I have no doubt that I will require help all along the way, until my civvy is all fixed. Thank goodness for forums like this that let an amateur like me work on my own car!!

[moldy]

g'day guys, now that i have my fan working properly, it seems that I am not losing any coolant at all. but...my dash board temp guage seems still not to be an accurate reflection of the real temp.

when the internal heater is on cold, the temp stays right down the bottom of the acceptable range, almost flat on the line. But when i have the internal heater on, the temp guage shows that the car is slightly overheated. never much above the top of the acceptable range, but still obviously not accurate.

anyone got any ideas why the internal guage would vary depending on whether the heater is on or not???

[fuzionz]

check your fuses, last it happened to a customers car and the recent mechanics that worked on the car bridged ( using wires ) instead of a relay or fuse