jmhenderson58

Okay, so I am having this same problem.

Car is Honda Civic 1996.

What have I tried?

1. Fan runs when directly powered to battery with leads.
2. Fan runs when the connector for the thermoswitch is removed and the connectors are jumped
3. 12Volts (as expected) in radiator fan relay circuit 1
4. 0 Volts (should be 12) in radiator fan relay circuit 3 when in Key On Engine Off position.

Diagnostics elsewhere say that #4 above means a fuse in the under the dash, driver's side fuse box is blown. Looking in my manual for the vehicle (yep, the original manual and still in the glovebox!), there isn't a fuse that is marked for radiator fan.

any ideas?

As an aside, it is a new radiator fan relay (installed yesterday) and a new thermoswitch (installed yesterday) and a new thermostat (installed three days ago).

jmhenderson58

I have a 96 Honda Civic 2 door coupe.

Daughter was driving it when it began to overheat.

Allowed engine to cool, topped off with 50/50 coolant and limped home.

I have to admit that recently I had wondered why the radiator fan was not running (I was under hood checking Automatic Transmission fluid).

So, once this happened, I began to suspect I had a radiator fan problem.

Did some online reading to find a diagnostic approach.

Here's what I've done, including a couple of out of step easy fix attempts:

Replaced the thermostat.
Replaced the radiator fan relay.
Replaced the thermoswitch.

Diagnostic steps:

1. Tested fan motor by disconnecting lead at fan end and supply power directly to fan. Result: Fan runs fine.

2. Tested power to fan through connector by disconnecting the connector from the thermoswitch and jumping the connector with paper clip. Result: Fan runs fine.

3. Tested power to radiator fan relay circuit under hood.

a. First, tested Circuit #1. Result: Shows 12 V (result varies 12.1-12.9). This result is the one expected for Circuit 1, as that circuit is always powered, regardless of key position.

b. Second, tested Circuit #3. Result: Shows 0 V (result never varies) in Key On Engine Off position. That result is not the expected result. 0 Volts would be expected in Key Off positions, but when the Key On Engine Off position is selected, this should be 12 V.

Based on the result of 3.b., above, I assumed that I would be looking for a blown fuse for the radiator fan, right?

So, I pulled the original 1996 manual from the glovebox, turned to page 198 where the interior fuse box diagram and chart appear. NO FUSE FOR RADIATOR FAN!!!!!

Ideas?

eghatch9295

iTrader: (1)

there is a fuse... off memory, #57 in the underhood box. might be wrong on the number, but its there.

mk378

Your result in your "test 2" shows that the the relay, fan, and fuses are all OK. The problem is either the thermoswitch, or something else is wrong with the cooling system and it will overheat whether or not the fan comes on. To test that, put the paperclip in and test drive with the fan running all the time. If it overheats, there is some problem other than the fan.

jmhenderson58

I don't see a #57.

I am attaching the two diagrams from my Honda manual.

jmhenderson58

So I jumped the connector after removing it from the thermoswitch (remember, the thermoswitch is new, replaced yesterday, as is the radiator fan relay, replaced yesterday). Jumping got the fan running.

Started the car up, took it for a drive. Still overheating ... ran the defroster on high to help dissipate heat on the way back and it kept it from redlining on heat gauge.

Ideas?

jmhenderson58

Here are the fuse diagrams for the under dash and underhood fuse boxes

mk378

Thermostat stuck closed? Remove thermostat and test it in hot water.

Or it could be a head gasket leak forming a bubble in the engine and preventing proper coolant flow.

If you are sure the fan was running all the time during the test drive, clearly it is NOT an electrical problem.

When there is no flow through the radiator (lack of coolant, thermostat stuck closed, clogged radiator, etc) no hot coolant can reach the thermo switch thus the fan does not start. It doesn't matter that it doesn't start because the car is going to overheat anyway.

fcm

Check water pump.

The "termo switch" supplies a ground to the rad fan relay, if jumping the switch turns on the rad fan all fuses and circuits are good.

That leaves the water pump or a clogged rad as the problem.

If water pump is original, I would start there. 94

fcm

It will not be marked rad fuse it is the fuse for the relays coil in the under dash fuse box, turn on the ign. and test all the fuses in the fuse box, make sure you test both sides of the fuse.

Most likely a yellow/black lead at the relay and output from the fuse box, sorry can not find my Civic wiring diagrams. 94

eghatch9295

iTrader: (1)

it is marked tho, lol... cooling fan fuse. 15 underhood.

jmhenderson58

As my wife says, if it was a snake, it would have bit you.

A friend pointed that out to me too, so I've pulled #15. Visually good. Continuity tested good.

Thanks!

jmhenderson58

I know that new thermostats can still have issues, but it is brand new (replaced three days ago).

Fan was on when I shut hood and took off on my drive and was still on when I parked and opened hood afterward.

Sounds like the next inexpensive test will be to sure that I have properly filled the coolant and bled any air. I'm going to tackle that during the day tomorrow.

jmhenderson58

Not sure if water pump is original, and it doesn't look to be terribly expensive to replace. Before I do so, do you know of any kind of diagnostic for failing water pump? I have read that poor flow through hoses when temperature is up is an indicator of either WP issue or clogged radiator. Anything more specific?

Former User

Properly bleed the cooling system and then go from there:

https://honda-tech.com/honda-civic-d.../#post39830585


There doesn't appear to be an electrical problem. I suspect that what you refer to pin 3 in your first post was not. Get the factory service manual for your car. There you will find diagrams like these:

jmhenderson58

Update:

Put front end up on my portable ramps ... opened radiator cap ... topped off fluid ... started car ... ran heater on low blower setting ... bled the bubbles out of the radiator ... had to retop about five times till all air out of radiator.

Car is no longer over heating.

jmhenderson58

Well, that seemed to be a fix ... the car was not overheating since the last post ... but we've also had unseasonably cool weather.

Yesterday temps hit the low 80s.

Daughter took car to the gym. Overheating as she drove home, had to run the heater on full blast to keep it from redlining.

Today, jumped the connector that would normally attach to the thermoswitch with a paper clip. Fan comes on in Key On Engine Off and Key On Engine On. Fan is running. Still, about 10 or less minutes driving local distance and speeds, it starts to overheat.

So, to review:

1996 Honda Civic Coup.

Replaced thermostat.
Replaced thermoswitch.
Replaced thermoswitch relay.
Lifted front end and bled radiator.

Still overheating.

Some additional notes:

Oil and dipstick are clean and free of any whitish deposits. There have been ZERO I mean ZERO vapor clouds from the tail pipe, no evidence of excess moisture from that tailpipe.

I am thinking maybe my radiator needs replacing because even with the radiator fan running I am overheating. The separate problem, why doesn't the fan switch on via the thermoswitch would be answered, wouldn't it, if the radiator is clogged?

jmhenderson58

Took awhile to get replacement radiator.

So.

1. Replaced thermostat.
2. Replaced thermoswitch.
3. Replaced radiator cap.
4. Tested electrical and:
a. relay is good
b. fan runs when jumped
5. lower radiator hose never gets hot
6. no milky or foamy appearance to engine oil and no white cloud or moisture emitted from tail pipe.
and, yesterday,
7. Replaced radiator.

STILL OVERHEATING!

I think that the next step is likely the water pump.

I've pulled and replaced alternators, replaced belts (other than timing belts/chains).

Is there any diagnostic for a failed water pump?

Is replacing the water pump a task that a shade tree mechanic can accomplish?

mk378

Water pumps pretty much never go bad unless someone has been using plain water or very old antifreeze mixture and corrosion has occurred.

You replaced thermostat but apparently never went back to test the new one in hot water to make sure it's not a dud.

Take the radiator cap off when the engine is completely cold and verify that the radiator is full. Then start the engine with cap off and rev it. If bubbles come out and/or coolant gushes out, head gasket is leaking. This is often the only symptom of a small leak. White smoke, tainted oil, etc. require a massive leak.

jmhenderson58

we NEVER use plain water. ALWAYS buy the premix.

actually, while I was doing the radiator replacement, I did pull the new thermostat out and stove top tested it and it appeared to operate correctly, opening at about 190F.

nonetheless, because I am a bit OCD, I went ahead and bought a second new thermostat and replaced it anyway.

as far as the bubbling ... one of the folks that provided guidance on bleeding the radiator to remove air indicated that bubbling would occur if there is air trapped. When I bled the radiator, that was exactly what happened.

I'm going to do as you suggest when my son gets off work ... so he can rev while I watch.

Former User

Did you precisely follow the bleed procedure instructions that I posted after replacing the radiator and thermostat?

jmhenderson58

I am a doofus!

That was you that gave me the instructions. Thanks!

I followed them precisely ... with the exception that we don't have an inclined driveway, so I put the front end up on my portable ramps.

Former User

In addition to mk's suggested test, also consider renting the block tester kit from AutoZone.

jmhenderson58

will do!

jmhenderson58

Well, I pulled off the radiator cap, and had my son start the car. Bubbling at start and when revving. I assume that this is what you were saying to look for.

Here's a link to the video my son took of the bubbling:


I'm running over to Autozone to get the test kit just as a double check.