Hey guys,

I'm having a problem with my 92 civic with a d15b2. It is completely stock and I put in a used radiator a while back, because the old one was leaking badly.
Ever since then, the radiator fan has not been coming on when the car is up to temperature (even when the needle on the gauge is over half, almost at hot).

The first thing I thought of was the fan switch at the thermostat housing. I unplugged it and jumped the switch with a paperclip, and the fan comes on. You can hear the relay clicking as well.
So i bought a new switch and installed it, which did not solve the problem.
Then I thought, maybe both the new and the old switch are bad, so I tested them both with a multimeter and they both seem to work. I tested it by heating them up with a lighter and checking resistance, not sure if that is exactly the correct way, but I thought it should work.

Today I replaced the thermostat because I saw that it was torn a bit and the lower coolant hose was getting warm way too quick after startup, which also didn't fix it.

I have bled the cooling system numerous times, but the fan still is not coming on.

Now I have no idea where to continue... When I complete the circuit by jumping the connector with a paperclip and the fan comes on, i basically confirm that all the wires and fuses etc. are fine, right?

Thanks in advance for your help

 

Start the engine, let it sit and idle, the fan should come on after about 20 minutes or so, keep an eye on the temp gauge. It should go to about 3/4 high or almost to the red before the fan turns on.

 

If the fan comes on with the fan switch connector jumped then everything else is working properly. Either the wires, at the fan switch plug, are broken inside and the wires connect when you pull it up to jump it, or there's air in the cooling system, or you aren't letting the car heat up enough for the switch to kick on. I believe coolant type can affect it too because when I switched from the generic green coolant to the Honda blue coolant I'm pretty sure my fan takes longer to kick on now so if you changed your coolant type that may be a factor. I'd start by pulling the terminals out of the fan switch plug and seeing how they look. If the tabs inside look loose try bending them a little, with a needle, so they'll make better contact with the pins in the switch. After that burp your radiator and see if the fan kicks on. Should kick on within like 5 minutes after the thermostat opens(check by the lower radiator hose heating up, as you mentioned).

 

Sorry for bringing this thread back to life after half a year, but I still have not been able to figure out this issue.

@fryman thank you for the tips, I actually plugged in a spare switch with the other switch screwed in the thermostat housing and heated it up with a lighter and the fan turned on, so it seems like the connector is fine.

Yesterday I bled the cooling system for over an hour (with letting it cool down for 15 minutes inbetween), so I am pretty sure there is no more air in the system. I had the front of the car jacked up and used a no spill funnel.

I am starting to think that the gauge is reading wrong and I am shutting the car off too soon, but it still seems very unlikely as I have actually installed an aftermarket gauge (with the sensor in the upper radiator hose), and the readout seems to be pretty consistent with the stock gauge.
When the stock gauge starts rising above half, the aftermarket one shows a little over 100°C / 210°F, which sounds right. It is a cheap gauge though so i don't really know how trustworthy it is.

I also looked up the resistance that the coolant temp sending unit for the cluster should have and I found this:
142 Ohm at 56°C / 133°F
49-32 Ohm at 85-100°C / 185-212°F

My sending unit has a resistance of 1260 Ohm at 9°C (48°F), which seems completely wrong, but it does go down a lot when the car gets hot. What confuses me the most is that the gauge in the cluster starts going over half at about 53 Ohm from the sending unit...
But according to the data I found on the internet, it should only start going over half at like 35-30 Ohm. So even if the sending unit is bad, it sounds like there is an issue between that and the cluster.
I already tried an old spare cluster that worked fine in the old car, but it did the same thing. I tried to get a readout with my multimeter at the plug for the cluster (black wire and green/yellow wire), but i couldn't really get a readout. I am not good with electrics though so that was probably a me-issue.

At this point I really don't know what else to test and I don't want to keep throwing parts at it, so I would really appreciate it if anyone has some kind of idea.

Thank you!

 

Check out this helpful video, was thinking though since jumping at the switch makes it turn on, may need to fish further upstream for the problem..

 

When I did a jdm gsr swap in my eg last year I went through the same thing. I let the car idle for almost half a hour with a no spill funnel hooked up to the radiator. This might sound crazy but it was cold outside causing the motor not to ever get near the temperature needed to cut the fan on. Soon as outside Temps got hotter it came on while at a stop light.

 

What brand thermostat are you using ? Do you have the coolant bypass hose ("U" shape from the thermostat housing to the intake manifold/cylinder head near the distributor) connected ?

 

Could your rad cap be faulty causing this odd issue?
I also recall another guy who had the exact same scenario, turned out being the new switch bought was faulty aswell..
Maybe try a different brand and if it doesn't work return it lol

 

could be a couple things
In Missouri, Its cold. My fan has not turned on in 2 months and the temp never goes above 3/8 the gauge even with the radiator blocked off about half way with cardboard. The little D series engine run cold so youl may not even have a problem
Could be that the thermostat is upside down. If you have a weep hole on the thermostat it has to be pointed up.
You replaced the radiator with a used one due to leaking. Could it be that the old radiator was so clogged up with crap that it made the car run hot? Now that you have a different/clean radiator the engine is now at proper temp
When driving, does the temp gauge go all the way up? If so, you have a coolant flow issue. If not then we know coolant is moving. If coolant is moving, we now need to find out what temp its at. Harbor freight laser thermometer is your cheapest bet. Drive the car for a half hour. Not let it idle in the driveway/garage. Drive it till the temp gauge is where its supposed to be. (all cars run a bit different temps, My civic runs just a hair below the halfway mark on the gauge, my wifes previous civic ran 1/4 up the gauge) . After the drive see what the temps are at the upper and lower hoses. (Im willing to bet that they will not be over 210 degrees F.) Now let it idle for 30 minutes (heater/ac OFF), checking the temps of the upper and lower hoses as it is idling. IF the temp of either hose goes above 225-230 and the fan does not turn on. then you have a problem. If not, then that just means you have a cool running engine and not a problem.
Good luck

 

since I have insomnia today (currently 404am central time) I looked around the interweb about this. Take out the coolant sensors under the distributor and either clean them off or replace them Thats the gauge sensors.

 

I appreciate the help guys!

The Thermostat is from Meyle. I do have a coolant hose from the thermostat housing to intake manifold. The hose under the distributor goes to the heater core on my car I think.


There is no steam or coolant coming out when its getting hot so I feel like that shouldn't be the problem, and the fan is also not coming on when I'm bleeding it with a funnel on the radiator and no cap installed.


I'm like 90% sure I put the little hole up, it's been a while though..
Last summer when it was hot outside, the gauge started going over half only at a red light, as soon as I start driving the temp comes down again.
That is a good idea, how much do you think the temperature differs between the hose and the actual coolant?

I think I'm actually gonna buy a new sending unit for the temp gauge because they are only like $5, so I can rule that out and have a little peace of mind. I am pretty sure the other one, the actual ECT sensor, is only for the ecu right?

Thank you guys!

 

The ECT sensor is for the ecu which is separate from the switch I'm pretty sure.. 99%, so replacing that would have no effect. If your able to jump the switch with the engine cold and the fan works I would rule out the ect sensor being a part of the circuit.
Maybe it is just too cold outside if your just letting it idle hoping for it to turn on? Try driving it with the cabin heat turned off and if the gauge starts showing over halfway pull over and quickly check for fan operation.
Have you tried doing a coolant flush? Have you ever put that crappy stop leak in your system which causes problems?
The jiggle pin on the thermostat should always be mounted at 12 o'clock to help bleed air through the system which you say you recall doing so that should be fine.
I had doubts on the rad cap but strange things happen all the time..
So.. Really it's narrowed down to being either too cold out, the plug for the switch is not making good contact, the new switch is faulty or there is blockage in the system (your used radiator mainly)- those would be my best guesses.
You could get a nice aluminum rad for around under $100 from ebay since that seems to have caused the problem..
I got one from AJP Distributors off ebay- the 2 row 92-00 civic manual half size civic one for my rex and it works and looks very nice, polished aluminum with absolutely perfect welds.

 

It has been my experience that only genuine Honda Thermostats work... aftermarket ones typically do not block the bypass hose when the thermostat opens and the weep hole at the 12 O'clock position may not allow the appropriate amount of fluid through in order to warm the fan switch properly. You can remove the fan switch and place the fluid end into boiling water and see if it closes... and if so, and you have already tested the car wiring by looping the fan switch plug and the cooling fan comes on, then your problem IS the thermostat.

 

Okay now I'm even more confused. New temp sending unit is doing basically the same thing, it rises above half a tiny bit earlier, but didn't fix it.
What i noticed though, when the car is way over half on the stock gauge, I'd say about 3/4 of the way up, as soon as I shut the car off and turn the ignition back on it is at the usual slightly below half temperature that I am used to from my previous hondas.
Does anyone know if that is normal? Is the cluster not sending 5V regardless? Or does it change depending on if the alternator charges or not?
Like I said I am not really familiar with the electronics..

Yeah I only replaced the sending unit for the gauge. The coolant is all new and it hat a full flush with distilled water. Never had any additives or stop leak or anything like that in it.

Okay but doesn't the fan switch get hot from the coolant returning through the lower radiator hose as soon as the thermostat opens? Or am I missing something there?

 

When you say the needle drops after shutting it off but returns not quite to where it was only in the ignition in on but the engine not running, does the needle go back up once you start the engine? Going with what happened, you replaced the rad and now a problem arises, I would replace the rad with a brand new one.
I've also never used a oem replacement thermostat and have never had a problem with an aftermarket so I doubt on oem being the fix, sorry JRCivic1... Everything you've ever responded to that I've seen has been nothing but pure knowledge and correct information and your a very smart guy.
New switch and sensors have no change so..

 

No offense taken Maxcapacity... new information has been provided by the OP and since the needle on the temperature gauge is behaving erratically, I would be looking more toward air trapped in the cooling system than a thermostat issue. If the needle is at 3/4 and you key off and immediately back on and the needle is at the normal position, this is an indication that there is air in the system. If air gets trapped around the fan switch, it will not function properly regardless of what brand thermostat is installed in the housing.

 

Yeah it goes back up immediately after starting it back up. I had it running yesterday and checked the temperature with the infrared thermometer and the temperature of both hoses seemed to be normal, there was about 10°C difference between top and bottom hose. Car not getting hot enough isn't really an option anymore because I heard the coolant bubbling inside the radiator when I shut it off.. Since the temperature is normal when I am driving I feel like it isn't a blockage in the radiator but at I agree at this point it seems like the only logical explanation. I found a new unused one second hand for 20€ so I will probably just try that.

Hmm I really felt like I got all the air out of the system but when I get the new radiator I will make sure to bleed it properly again. Do you have any tips for getting all the air out? I always jack up the front and use a no spill funnel, pinch the hoses a bit to push the air out and then run it for 30 minutes or so while sometimes revving it to about 2000 rpm. Is there anything else I can do?

A waterpump issue doesn't seem logical either right? With both rad hoses getting hot and temperature behaving as it should when driving.

 

Maybe just try bleeding the system with the car level on the ground, that's what I've always done with zero issues. Does your motor have a bleeder nipple on the cylinder head port where the upper rad hose connects? Starting with a cool engine - Run the engine with rad cap off and top it up until full, burp the upper rad hose and refill until full again, once the coolant has starting heating up and almost coming out the rad neck put the rad cap on and then use the bleeder valve to get out the remaining air until a steady stream is coming out with the car level on ground.
Could try using a new rad cap for shitzngiggles, your old one may not be holding adequate pressure to raise the systems boiling point and might not leak out coolant on the ground but into the overflow tank and may leak in air when cooling down so it's also important to have the overflow tank filled to the hot line when the engine has heated up so it does not draw air in if it's too low.

 

If you heard the coolant bubbling that means it is boiling. That indicates a bad radiator cap. You won't see steam as it pushes into the coolant recovery bottle and gets sucked back in when it cools. Your coolant is boiling being the cap isn't pressurizing the system. The cap is supposed to hold about 16 PSI before opening to the recovery bottle. The coolant at 16 PSI has a higher boiling point than when it has less pressure from a bad cap.

It can also be letting in air pockets causing your erratic gauge readings. JRCivic1 I believe already mentioned that cap. I thought I'd reiterate and explain why you wouldn't see any steam if it was failing. The caps are inexpensive.

 

What could be the cause if it never comes on ?

 

did you ever figure why the fan wasnt comming on ?
Im having the same issue..