Temp Sensor Removal

[mkmskm]

My temp gauge doesn't work so I put a 9V battery to the lead wire and grounded it and the gauge works so I figure it must be the sensor. I got a new one but I can't get the old one out. I don't want to use too much force because the head is aluminum right? I've put some Kroil in there but will it be easier to try and crack this loose when the engine is cold or hot?

[2ndwind]

It depends on what the sensor base is made of. I just put one in my car. I didn't pay attention to the base. However, in general (depending on alloy) the thermal expansion of aluminum is greater than that of brass or bronze and even more so than steel. I'd say it would be a good bet to get it up to engine temp, then remove sensor BUT, BUT BUT, the water will now be under pressure and cause a very unpleasant experience (think trip to the hospital) if you take it out when hot.

I would get the engine up to temp, put a wrench on the sensor and hopefully break it free, about 1/2 to 3/4 of a revolution, let the car cool down A LOT (several hours?), relieve the pressure at the radiator cap then remove the sensor.

[manoa matt]

The temp sensor sits low in the head and there is a good amount of coolant above it. You'll need to drain some out, about 3/4 of a gallon, or when you remove the sensor the spark plug valleys will fill up with coolant.

[2ndwind]

I replaced mine when the engine was cold. Had the new one handy, put my finger over the hole as I was removing the old one, slipped the new one in. Lost between 1-2 oz. of fluid, mopped up with towel. Stuck corner of paper towel into the only spark plug valley that got any fluid. Capillary action works just like the commercials! Topped off fluid at heater hose tee I put in earlier this year. All's well.