Help! Needle going above red, then down again...
 

This weekend, I found my temp gauge was going ABOVE RED when starting up. On my way to school today , I pulled over, touched the engine and it didn't seem...abnormal, then got back on the road, and the needle went back down.

Here's what I've tested so far...

Thermostat:
-Tested Ok

Sensor B (Towards front, #18 on picture below)
-Could not test acuratly (can't get water above 215*F, tried torch near bottom) DID turn on...so not suspecting it.
-When plug jumped:
=Car off: Turns 1 fan on
=Car on: Turns 0 fans on

Sensor A (On thermostat housing, #17 on picture below)
-Tested Ok
-When jumped
=Car off: Turns 0 fans on
=Car on: Turns 2 fans on

http://www.slhondaparts.com/images/PCI/13SV40/027/8.jpg

What could be causing this? What sensor does the needle get it's reading off of?

and this is for a 1994 accord lx (f22b2, auto)

have you check the main relay? I had the same problem 2 winters ago and it was just a relay that needed to be replace.

which one is that?

I don't think those are the right sensors as the temp one is usally a 1 wire job under the dizzy it's #15 on your picture it sends a varable ground siginal to the gauge when the engine warms up . the other thing that could be bad is the temp gauge .

A (#17) & B (#18) are the 2 fan switches. From your description it sounds like the circuit controlling your fans is OK.
#15 is the sender for the gauge.
#19 is the coolant temperature sensor for the ECU.

Look for an intermittent short to ground in the wire for sender #15. That would give a bogus high temperature signal to the temperature gauge. Or maybe sender #15 is just going bad.

Check the coolant in your radiator. It's possible to have air pockets in the radiator & hoses, while the reservoir bottle is still full. In this case the sensors will see strange things.

Hey DIYGuy,

Did you ever get this problem fixed? I have the exact same thing going on, I bought two new sensors (17 and 18) before i found this post. I think i also need a new #15, because of the same symptoms, my car's temp gauge read's all the way hot, even after sitting outside all night in below freezing temps.

Does anyone know the Honda part number or correct name for sender #15?

Thanks!!!!