Can't figure this out for the life of me, hoping someone here has had a similar problem/experience and can maybe point me in the right direction on what to do next. The car seems to run fine, but will start overheating after 15-20 miles. Here's a list of things I've done/noticed.

• Changed thermostat (Honda OEM)
• Changed Thermostat Fan Switch (Beck-Arnley) fan is working now, it wasn't working when I originally noticed it was overheating, but even working the car still overheats
• Changed water pump (Old one looked fine tho, but it was overdue for a timing belt change anyway)
• Radiator is only a year old, had a small leak in it last year and replaced (Napa radiator with Napa radiator cap)
• Flushed the radiator and upper/lower hoses when I did the timing belt.
• Did a combustion gas test multiple times, came back negative. Fluid seems good tho, reacts to car exhaust/exhaling.
• Radiator is still filled with coolant when I did the water pump change (2 weeks ago)
• Car heat works fine

If anyone can give me some advice I would appreciate it, this car use to be super reliable.

 

How do you know the car is overheating? What tests have you done to rule out faulty coolant temp sensor and/or wiring, or faulty dashboard gauge/wiring?

Also, what it your coolant temperature and how did you measure it?

Finally, how did you purge the coolant system of air?

 

1. None. I'm relying solely on the temp gauge in the car, it seems to be working fine (afaik) it starts out cold and rises normally to the stable temp when running, then will just go to overheating. I'm not getting any check engine lights (I think that sensor will throw a CE light when faulty).

2. I haven't measured the coolant temp with a thermometer but it is definitely hot to the touch (coolant hoses) and will steam with the radiator cap off, etc.

3. Parked on an incline, heat to max, radiator cap off, let it idle for a long time 30+ minutes, topped it off as it went down (didn't take too much additional coolant but it did take some). I've done this multiple times, sometimes letting it idle, sometimes putting it at 1000-1500 rpm for a bit and then letting it idle.

 

The best way I can think of to test the dashboard temp gauge is to point an IR gun at the radiator and/or hoses and read the value. Compare that with the coolant temperature reported by your gauge and by the PCM using a scan tool. Low-end version of both pieces of equipment can be found for ~$20 each.

Another way to look at it: imagine your dashboard temp gauge is bad. How much trouble is it going to cause you to continue relying on it?

I don't know if that's the problem, but I'd be interested in gathering as much data as I could before changing any more parts.

Is the top hose hot and bottom hose cool [hot but cooler than the top hose] at operating temperature? That's how it should be. An inefficient radiator could give you a hot hose on the return (bottom). A blockage could give you cold intake (upper) hose.

 

Upper is hotter than lower, but lower is still hot-ish when the thermostat opens. I have an OBD II scanner but idk if mine will tell me that info, i've only used it once to see a code years ago. Is there anything else it could be besides a faulty sensor/wiring?

edit; the radiator is only a year old, also

 

There are many - that seems to be the problem. I'm not sure of any reliable, cost-effective way to get to the bottom of this other than to methodically and conclusively rule out every one of them by collecting data.

The technology has come a long way since then. For example, you can pick up this well-reviewed model (worked for me on a sixth-generation Civic) that connects to your Android and iOS device via Bluetooth:

https://www.amazon.com/BAFX-Products...AHS/ref=sr_1_1

 

Its not a mystery if its overheating.

 

Thats true but idk what's wrong

 

My understanding is there are 2 coolant temp sensors - 1 to report to the gauge, the 2nd is what the ECU uses. Does your fan turn on when the gauge shows you are getting hot? I had that sensor die on me once. If jumpered the connector the fan would turn on and temp would maintian. If I plugged connector back into sensor - no fan. Perhaps your coolant temp sensor is bad?

 

Sensor on the thermostat housing is the fan switch

Sensor on the front of the cylinder head Infront of the dizzy is the ecu temp sensor

The sensor under the dizzy mid way back on the head is the gauge sensor

I would suggest replacing the gauge temp sensor first.

 

What is a dizzy.

 

dizzy is when you spin around long enough to fall over.

http://www.ebay.com/itm/Richporter-Technology-HT04-New-Distributor-/192025068183?fits=Year%3A1998 Model%3ACivic&hash=item2cb5960297:m:mnSICX2MXae58d 1oAqA1eUw&vxp=mtr

 

I don't know how that name became to be at all, its called a distributor.

 

Do you think that sending unit is worth replacing?

 

i dont like the temperature difference between the hoses when the tstat is open. they should be nearly equal.

 

Correct, the guy who said the top should be hot and the bottom cool is wrong. That's indicative of a bad thermostat.

OP, have you checked the level of coolant after overheating? Is it leaking anywhere? You can check the resistance of the coolant temperature sensor with an ohmmeter, I don't remember off the top of my head what the readings should be but google should have that answer for you. If it is out of spec, replace it. If not, you're looking at a possible leaking head gasket.

 

I just had this problem OP. You either have two issues here. Fan control relay or the temp sensor on the side of the head. Both are cheap and easily done so I would recommend replacing both, since you have basically over-hauled your cooling system already. Change the coolant temp sensor that's on the cylinder head. Fans come on late, but only after car begins overheating? My situation, I had recently over-hauled the whole cooling system. Had over-heating issues after few thousands miles later. Basically the temp sensor is shorted. Telling you car's ecu that the temperature is lower than it really is. In turns not letting the fans come on. Hope this helps, this one kicked my butt. Only because it was a combination of the fan relay and this engine temp sensor.

 

This guy!

 

My mistake, lazy language. What I meant to say is that the bottom hose may be cooler (but still warm) than the top hose under normal conditions. Coolant leaves the block, entering the radiator through the top hose. After heat exchange through the radiator, the coolant returns through the bottom hose. Heat has been removed so the return hose may feel cooler than the top.

A warmer upper hose doesn't necessarily mean anything is wrong with the coolant system or engine.

 

yes, it does. once the thermostat opens, the hoses are nearly the same temperature... nearly as in your hand wont know the difference.

 

So change the ECU sensor on the head, not the sending unit to the gauge? Man I will be pissed if it was only that sensor... also extremely strange if it is the case, replaced an o2 sensor about a month ago, fan switch sensor, and now this? What is causing all these electrical problems.... Also shouldn't that sensor be throwing a check engine light if its bad?

edit; someone above you said I should change the sending unit sensor first, maybe I should just change both to be safe lol.... they're not cheap tho :\

 

Go up to your local auto parts store and rent a coolant system pressure tester and the import adapter fitting. It's a hand pump that pressurizes the radiator and hoses to check for leaks. Pump it up to 1.1 bar or about 15 psi and see if the system holds pressure at that level. If pressure does drop you have a coolant leak somewhere, it's usually the U shaped heater hose behind the thermostat.

Also I would purchase a laser temperature gun also available at any auto parts store or harbor freight to take a reading of the temperature of the cylinder head by the distributor to see if it's actually over heating.

You could also have a clogged heater core if your heater isn't working.

Giving me **** about calling it a dizzy lol. Comon man I can use slang terms

 

That is the one for the ecu. When that one fails it typically causes hard starts because the ecu can't calibrate the correct fuel to add at the correct temperature

 

The sensor is cheap. I got mine for 7$ on eBay , here one for 15$ FAE brand is an OEM vendor for a lot for German brands i.e. VW, BMW . So it is a quality sensor. http://www.ebay.com/itm/FAE-37870PJ7003-Engine-Coolant-Temperature-Sensor-/121958098107?hash=item1c6544e4bb. The relays are about 15$ a piece pricey for a relay, careful Honda will charge you about 40$ for the "Newer" vendor. But the old stock ones are about 10-15$ you just have to research the part #s

 

The fan switch can be an issue, I saw that you purchased an aftermarket one. With parts like this I would recommend to stick with OEM, I've learned this from trial and error. Aftermarket tends to be cheaper because the NTC inside the sensor is a cheaper one and doesn't have the same specifications as the OEM one. Which can cause your fan to turn on but too late causing the temp to "overheat". You can take the cheaper route and it may work but not all the time. I've had a fan switch brand new from Autozone shorted internally and as soon as ignition was on the fan was on and never turned off, also as stated previously I've had one that didn't have the correct thermistor installed and the fan would only turn on when the car was overheating.