Tossing this one in here and calling out to the 3100 guys.

Looking for the location of the temp sender that supplies the pcm? Not sure if it'* a single sender with dual element or two senders.

What temp does the pcm command the fans on at?

Where should the fan relay be located?

Situation: My little sister had an issue where the temp nearly redlined and heat in the cabin disappeared. It then came back to normalish temps and heat returned. This flucuation began happening about a week back, has been happening since. I suggested she add coolant and ensure it'* topped off like i have shown her in the past. Holler if that doesn't fix it. Apparently going to the boyfriends place (an hour away) for the weekend is more important than the longevity of her car. She texted me yesterday that the problem was still happening.

I got her car into my garage last night and though this should be an easy locate leak, fix, top off and bleed the system. Car smells slightly of coolant external to the radiator, looks like the LIM'* may need to be done again, it'* been 5 years. For now I'll the night I'll top it off and order the gaskets. I pull the overflow (pressurized overflow tank/only filling location) cap and the coolant is a milky white. Check the oil, it'* super clean, converstaion reveals it was changed Friday before the trip. Pulled the valve cover cap, it'* clean and everything in there is looking like it should. Check the trans fluid and it'* dirty red. Just like i expect in her car.

Here'* the thoughts.. engine oil and coolant mixing cause milky foam in the crankcase. This makes sense that it'* in the crankcase and not the coolant because the only places where coolant and oil can typically mix in a motor is in the heads. In the head the oil is pumped up in the lifter, through a pushrod and then splashes off the rocker and drips pressureless to the crank case. And coolant in the head is under ~16psi. Coolant into oil, very rare for oil going into coolant. Well the trans has up to ~170psi in it and has a trans cooler in the side of the radiator, this could push trans fluid (aka red oil) into the coolant, but it would be reddish and dirty looking. This is not.

I asked my sister what color coolant did you add when you added it the other day. "I dunno, I used that little bottle you left the last time you worked on the car." Meanwhile I'm thinking..last thing I did was ps lines and since when does coolant come in a "little bottle", it only comes in gallons. She proceeds to pull out an empty bottle of ps fluid and hands it to me. I turn the label for her to read and she understands that she is the cause of the whiteness. Not only that...but she added less than a quarter of a quart of fluid to a system that was probably two quarts low. Wonder why that didn't fix it?????

A coolant flush and refill later the car is staying pretty consistent. I like to see the fans come on etc and they didn't. Cold rainy night I was not fighting to get the car over 220F as it didn't want to heat up more than that. The fan at first didn't come on with AC request. Confirmed the compressor was on, then fiddling with the buttons etc it did come on and continued after that. Has me wondering about the relay or fan itself. Hence my pointed questions before the entertaining story.

It'* been a while since I've worked on a 3100, but if memory serves me correctly the coolant temp sensor should be under the throttle body in the lower intake manifold. I'm not sure if there were two sensors on that motor, but if there were look on the front and rear center of the block. There are two spots that are typically plugged that a sensor can be. You can see in this picture of my 3500 that it'* to the right of the Oil Filter.


The coolant temp sensor on my 3500 is located on the rear head on the drivers side. So there are a couple different places it could be. It'* likely just the one on the LIM.
I'm not sure when the fans kick on. It seems to me like it was 210* but I'm not sure. The fan relays are in the fuse panel in the engine bay. I know that you can ground one relay and it will only turn on with key on, essentially running all the time. But grounding the secondary??? will leave the fan on at key off.

Good luck!

Was the good luck for the work or not killing a sister? Really..I have spares..lol

On my 3.1 sfi its next to the throttle position sensor, yellow and a black wire.

95 ols cutlass ceirra, 3.1 sfi

My fan come on at about 227 degrees stays on until about 195

Fan relay is under hood pass side front, fan 1 has red, pink,dark green,light blue wires.