llltrunkslll

Hello all,

I'm new to this forum and have been checking the FAQs and haven't found anything that has spoken to my specific problem. I have '00 Civic EX (all stock) that overheated. There was white smoke from under the hood and when I opened it the radiator overflow tank was boiling. I let it sit overnight (it was late) to cool down and checked it the following day.

The overflow tank was nearly empty, but I'm not sure that it didn't suck up any air during the cool down. I re-added coolant fluid to radiator and overflow tank. I then followed the steps that I could find by google, and the best that I could find was "Tegger's Guide".

In summary, this is what I've done: (Engine ON) Let engine temp rise until dash gauge read up to 3/4 of Max, but fan still didn't come on. (Engine OFF) Checked all fuses by eye and used a multimeter [looked fine by both]. (Engine ON) Turned ON the A/C. A/C fan came on, but NOT radiator fan. (Engine ON) Disconnected the engine coolant temp sensor plug and shorted wires, Radiator fan came ON instantly.

After replugging in the sensor, I also repeated the above after switching the A/C and radiator relays (same part so they are swappable), just in case that was the issue somehow, but results were exactly the same as above.

To me this suggested the cooling fan switch was bad. I replaced it with an aftermarket switch (from autozone). I didn't drain the radiator fluid, just did a fast swap. Checked there were no leaks (all looked great) and restarted the testing. Fan still does not come on unless I short the switch (by touching the tips of my pliers to plug socket)... When I checked the resistance at the NEW cooling switch (engine cold) got a reading of '0F' or infinite resistance [Normal]. When engine was hot, I rechecked and still got '0F' [Abnormal]. It's very unlikely to get a bad new part, so I'm not sure where to go from here. ANY help, please, would be greatly appreciated.

delsolproblems

Use a laser thermometer to make sure the temperature at the switch is 195 or above when you test the resistance.

jdeemseerx

did you check to see if the thermostat is opening? are both coolant hoses getting hot? by shorting the plug to the switch and the fan coming on it means the wiring and relays are ok.. if you checked the new switch correctly it means they gave you a faulty switch..it happens, i work for honda and sometimes even from the warehouse we get parts that are bad.. the easiest way to check is to boil water and hang the switch dangling in the pot of water.. and measure the resistance as it slowly cools down.. by the way when the coolant in the overflow tank is boiling it usually means one of two things,.. your radiator cap is faulty or you have a blown headgasket..

strategy400

I bet the headgasket is toast. How many miles on the engine?

civictyper955

Same thing happened to me a couple of days ago. I changed the thermostat, ECT, and Fan switch then drained and filled the radiator. Good LUCK!

llltrunkslll

Thanks for all the replies!

I want to clarify a couple things in response to the posts. I'm not sure I conveyed it right regarding the overflow tank. The fluid was boiling because the radiator was so hot the expanded fluid (overflow) was intentionally vented to that tank. Since it was so hot and without adequate pressure, the fluid would (as it normally would) boil at atmospheric pressure. It does NOT produce noticeable bubbling in the overflow tank NOW while running. To be clear, I was NOT saying that the engine running was forcing air into the radiator.

In regards to the hose temperatures while Engine warm: the top hose was warm to touch leading to the radiator and the bottom hose remained cool. Seems like that is normal so thermostat should be good. On a side note, I'm not sure why that would interfere with cooling fan operation when the engine is hot, but would suggest problems with thermostat or hose/radiator is airlocked.

Is there a second switch in the mix for this model/year car? I'm really puzzled on whether or not while the A/C is ON if the Radiator Fan should run EVEN IF the fan switch is broken! From what I've come to understand it seems like a dead cooling fan switch will prevent the fan from turning on, but replacing the fan switch should fix both cases (the overheating and allow the fan to come on when the A/C is on).

Thanks in advance for any clarification or help.

llltrunkslll

Sorry for the delay in responding, work has been grueling with long hours.

tommyboy4

I had a blown head gasket do the same thing.

bluesteel29

replace rad fan switch and check for rad hoses for pinhole leaks

darkenedsol

Hmmm.... sounds like you may have gotten a bad switch. Not to worry it happens-that's what warranties are for. It sounds like your testing is headed down the right path-however, I had a question regarding your saying the lower hose was cool. After the engine has warmed up, for 5+ minutes, is the lower hose REALLY cool? Because normally the thermostat should open if it's functional and allow the lower hose to come up to temperature and should feel warm to the touch. This means the thermostat has opening and is allowing coolant to circulate through the cooling system. Keep us posted on progress/findings! Good luck!!!

salbaje

try jumping the fan and see if it works. if you jump it and it works your fan switch is bad

quilksilver

change your thermostat first, you never stated that you did if i was you i would of done that first

llltrunkslll

Hey, post is still alive. Just hard to find time with work again.

I was just able to pick up a laser thermometer today so I'll give the car a warm up tonight and check the resistance on the fan switch to confirm the fan switch is the problem. I installed the current one with a 24 mM deep socket wrench, so should have been good.

In regards to the lower radiator hose being cold, it is ~20°F on average now and I haven't been running the car for a long while (except while testing) to avoid any further damage to car until I can figure out what exactly is wrong. Since ambient temp is quite low I'm thinking the lower hose just feels cold due to that and not a thermostat issue (yet...). Thanks for posts so far. Check back for my results.

llltrunkslll

I checked the temp last night using the laser thermometer on the cooling fan switch at the copper base and on the metal housing where it bolts into engine. The whole thing was only ~168 degrees F. The resistance was still infinite (off) for the fan switch. At this same time my temp gauge in the car dash was reading over 3/4 of Max temp. Checkingt the temp on enginge block and hoses, the temp was 197 and 198 respectively, but bottom hose stayed ~50 F. I've read that the switch doesn't turn on until 195F. It follows then the switch wasn't a crap part if temp isn't sufficient to turn it on, but then my problem is now something else. What are the symptoms of a bad thermostat? The hose TO the radiator is hot, so it seems like the thermostat is working since it opened enough to allow flow into radiator. Do I have an airlock then?

dpetro1

both upper and lower radiator hoses should be equally hot. if they arent then your thermostat isnt opening. this can be caused by either a bad t-stat or air in the system.

i suggest draining the system repalcing the t-stat and then refill the system and let the car idle with the radiator cap off to allow air to purge from the system. watch the fluid level and add coolant as needed. let the fan cycle twice then replace radiator cap.

if the temp guage starts rising above normal before the fan comes on try pumping the hoses with your hands to help the air out. also jacking up the front of the car will help the air out