pantdino

As the title says, what are the temp vs resistance specs on the engine temp sensor on the head?

The temp gauge on the 04 LX I just bought is sometimes on at about 1/3 range and sometimes way at the bottom (which I assume means infinite / very high resistance)

I get the P0128 code--coolant temp below thermostat reg temp or something similar

I don't want to spring $59 for a new OEM one and then find the problem was not the sending unit.

Thank you

ezone

Or it means the engine is really heating up and cooling down that much.


Elaborate on the conditions when you see this happening.


Think about why I would highlight that one word.......

pantdino

Car is cold in 70deg F weather. Gauge reads way down the scale, unnaturally low. You are driving a few minutes and happen to notice the gauge reads 1/3 scale. then you look again a few minutes later and it reads dead bottom again. then you look again and it reads 1/3.

That, along with the code, makes me think it is the sender or the gauge itself. All the while the engine is running perfectly.

I saw a video on youtube where it states the resistance cold is ca 2500 ohms and at 200 F it is about 275 ohms. Does that sound about right?

EDIT-- video was for a VW, which might have different specs from Honda

pantdino

update-- at ca 60deg F there is no continuity between the pins on the sensor--- shows "1" w scale set at 20 ohms

on my way to $tealer to get replacement part after reading about malfunctions with non-OEM parts.

Jim

ezone

A scanner that can give live data would be a big help. That way you could read the actual temperature as it were seen (interpreted) by the computer.


If you let the car sit still and get all warmed up (gauge should rise smoothly with no dropouts during warmup as long as there is no wind to cool off the radiator), until the temp gauge is in the normal middle area.............
Then if you go drive it and see the gauge drop when you are moving at speed, that usually means the thermostat is stuck open.
The gauge goes back up to middle after sitting still for a while and running (if there is no breeze to cool off the radiator).


Change the scale until you get a reading. A cold sensor should have much higher resistance than a hot sensor.



I don't really have plain resistance specs for the sensor.
Most specs I use are in voltage output, as seen in a live and working circuit (4.5v-0.5v) or in degrees on my scanner. I use a scanner, then if I need to, I can verify the data I see with a real thermometer of infrared gun.

I do have a note of my own from a 99 CRV (of all things) that 178 degrees F on the scanner was obtained using 270 ohms in the ECT circuit. IDK if it is the same on a newer Civic.



And yeah, some aftermarket parts are just poor.

pantdino

update-- I replaced the sensor and now the gauge rises progressively to about 1/3 scale and stays there as you drive

But another problem-- with the radiator hoses reading 186 and 196 with the infrared gun the fans are not coming on

Jump wiring the connector turns both fans on, so apparently the fan switch by the t-stat is bad-- will remove and test the switch after it the car cools off.

Thanks very much for your help, ezone


Jim

ezone

That's OK right now.

The lower hose temp has to reach the fan switch threshold, not the upper. The fan switch is sensing the water temp coming out of the radiator, so it can take a good long while before it's hot enough to run the fans. If there is any breeze at all, it may keep the radiator cool enough to not need the fans to run.

HTH

pantdino

The lower hose is the one that read 196, while the upper read 186. My guess is that the upper hose is sitting above the rad in cool air while the lower one is closer to the block and getting radiant heat, hence heating up the outer surface of the hose.

I wasn't brave enough to let it keep idling to see how hot it would get.
The seller replaced the rad hoses and filled the system with water rather than coolant, so bad things will happen not much above 212.

I got Honda coolant to fill the system with as soon as I get the system working properly.

ezone

That can't really be a true reading, the lower should never be warmer than the upper. The radiator cannot create heat.

I suspect a reflectivity issue may be skewing your temp gun readings, that's super common.