Erratic temp readings.

[henry]

I'm getting erratic temperature readings, even when I disconnect the water temperature gauge, the temperature sometimes keeps on reading 260 but the engine is running cold.....!!!!!?? and the next minute goes back to normal. This happens specially with the AC on.

Any suggestions

[mbouse]

The way our cooling system is designed, the radiator is not the highest point in the cooling system. Therefore, frequently air is trapped in the head, causing issues; this is the #1 cause for most cooling related issues. You need to assure yourself that this is not the case. I sent you a picture via email of a Spider with a T-fitting installed in the heater hose. This becomes the highest point of the cooling system, and when used to add fluid, eliminates air pockets. Best tech tip of the day. install one of those T-fittings and use it to fill your coolant system.

Secondly, do you understand how the two sensors work for the thermometer? Those sensors are heat activated grounding switches, completing an electrical circuit to the gauge. If you are getting false and erratic readings, either the sensor is bad, the gauge is bad, or the wire in-between is grounding out somewhere. Have you checked your engine temperature with a hand held laser thermometer to see if the erratic gauge has any merit?

Does the wild behavior act instantly when you turn on your air conditioner, or only after the A/C has been running for a while? if it is instanteous, i still suspect an electrical issue.

[henry]

I run the car with the A/C on all day today and no problem

[mbouse]

process of elimination will find the root cause.

are you CERTAIN the cooling system has been purged of all air pockets? this is the most likely cause of erratic cooling issues.

if you cannot stick a T-fitting in that heater hose, then try this procedure:
http://webpages.charter.net/mbouse/Blee ... System.pdf