Ok i know the ECU is supposed to activate the fan at somewheres close to 220* right? well i have a gauge that has the temp probe in the Drivers side head and it must show way different from the ECU's intake manifold temp.

I ask cause today i was driving around and i parked and got out of the car i was out for probably all of 2 minutes. i had looked at the gauge before i got out it said 200* about what it says running down the highway so i figured that it was the normal running temp for this engine. well i got back in and started the car and noticed that the gauge said 260* i go WTF and reach to hit my fan switch but then i noticed that the fan was on already but my switch said off, after about 30 seconds the gauge said about 240* and the fan shut off, i was thinking i had a problem with the switch so i took it all apart and nope the fan switch i installed had no problems.

Is there really THAT much differences between what my gauge reads and what the ECU reads cause of there different locations? ECU has a good fan chip cause when you put it in diagnostic mode it turns on so thats not fried, the origional ECU had that part fried tho.

P.S. the CTS is only about 8 months old.

 

It's tough to say. There might be a problem with the CTS or with your temp sensor. The best way to tell is to borrow a infrared gun from someone and take a readin with the fan on and one with the fan off, both at the t-stat housing.

But there could be a difference just because the heads are directly heated while the intake is indirectly heated, the Coolant temp should be close though.

 

Can a code reader tell what the CTS is reading? im not meaning one of the cheap ones but one o the big ones like my college has.

 

A diagnostic machine can read the ecm and tell you what the cts is, yes.

Both sensors should be reading fairly close as its reading the coolent. But after setting a few mins, they could read differently as the fluid is not being moved and create "hot and cold" spots within the fluid.

 

Only if it's like the Snap-On Red Brick where you can read live data, but Dale is right, they should be fairly close in temp since they both read coolant temp, there should only be a couple of degrees difference.

You can just read the voltage of the sensor with a DMM and then cross reference the voltage table for it. That's way easier than trying to get a hold of a scanner, and a lot more accurate because the computer will substitute values if it thinks there is something wrong, but won't always turn on the SES light.

 

well where can i find this voltage table? and do you think that if my ECU fried it would take the CTS with it?

 

hey i can't help you with your problem i was just wondering what all you did to run the switch for your fan....i thought i read it somewhere on here but cant remember...can you help me out??

 

Ok I will try to clarify some things...

If you drive your car and it gets warm, like it is supposed to do. Turn it off, but leave the key in the position where the guages still function. You will see the temp rise.
That is perfectly normal.
Is the coolant circulating through the radiator with the fans on? Of course not, the water pump is not spinning, and the fans are not on. So the heat soaked fluid will rise in temp as it continues to soak up heat fromt he hot metal engine.
What you thought it would start cooling down immedately after shut off?
Granted the heat source is no longer there, but neither is the cooling source.

I recollect a post that tomp said his climbed to as high as 260* before and it scared him. That is nothing out of the ordinary.
As soon as you provide the power to the system, the fans will kick on and the temps will go back down.
While you could install a time delay on the fan to keep it running after shut off, that really would not doo too much as the coolant is not flowing...

Also, the CTS and Guage sensor are in two different spots, but still on the "hot" side of the coolant. So they they would (or should) be close. But they also have different purposes. The guages sensor is well.. duh... the CTS is for the computer to control fans. And if you want to run a manual switch, I really suggest leaving the factory control there, but just add another "hot" source to turn them on when the ECU has not. That way incase you forget to switch it, the ECU still can.
just a little explaination and my

 

Oh i was not bothered by it rising after i shut the car off i was just adding that so yalls wouldnt think i was stupid and let it get up there by not activating the fan. it is just common since that it would rise like you said.

Its just that i have never let it get that hot before i am just trying to figure out if it sounds like the fan was working properly and my gauge is off. Fan used to run non stop as my AC pressure switch was unpluged. i repluged it and i have not let the temps rise above what my gauge reads as 220* it usually reads at the most 200* on a 95* to 100* day with the fan off running at 55mph. Im just trying to figure out why my fan would just turn on when the gauge reads 200* normaly. the only other peice of info i have is that it will climb to about 240* after a cold start up and then drop to normal temps and stay there for normal running but the fan wont turn on on its own as high as i have knowingly let it climb which is right at 240* indicated before i activated the fan manually.

If you want to do a manual swith just locate the Fan relay and take the ground wire that leeds to the ECU T off of it and run that lead into the cabin of the car through some opening where it wont interfere with Pedals/moving parts, then get your self a switch and mount it where you like. Run the wire you ran from the engine bay to one pole and then run a wire from the other pole on the switch to some ground. It dont need to be that great if a ground as all your grounding is a small amout of current that activates the felay. Functions in the exact way the ECU does but you do it manually, this will also allow you to retain the factory control of the fan. like on mine where it may not activate the fan where i want it to but atleast i now know it wont let my car go above 260*.

I used this switch as it matches the interior of the car well and i mounted it in the empty panel below the headlight switch. RadioShack.com - Cables, Parts & Connectors: Component parts: Switches: SPST Rocker SwitchBlack

 

That's because you have a lazy T-Stat in it.

I know this sounds like a silly question, but it's somthing that hasn't been asked or answered...it's full of coolant, right? Air bubbles will cause problems VERY similar to these. When was the last time the radiator cap was replaced?

 

2 months ago and i had it flushed, checked for leaks, and filled at the local GM dealer ship cause i was told of that being a possible cause by a friend, cost me 60 bux! it has not lost any coolant. i have yet to add any and the reserve tank is still just as full as it was after they got done. radiator is full to.