Jeff91RS

iTrader: (1)

I bought my car in mid December and kept it stored until the snow melted, not because its a beauty queen but because I have other cars and i didnt need it right away. well last friday i pulled her outta storage, checked all fluids, and all that other fun stuff and took her out. In northern Il we are lucky to get 40-50degree days but last night i left my camaro running while i was in the house for 15-20 minutes and the temp gauge peaked and the overflow tank was boiling vioently. After stareing at it like a moron for a minute i closed the hood and drove it around and cooled almost instantly. I am fairly certain my cooling fan wasnt running. My question is does the cooling fan turn operate off of the same sensor as the guage?

yes i know i was stupid to leave it outside running but i was around 30 degrees outside. and yes i am aware i might have caused some serious engine damage

sofakingdom

iTrader: (1)

No. The gauge is ENTIRELY separate from the cooling system.

You don't say what kind of car you have. In some cars, the fan is controlled by a switch in the pass side head; and in some, there are 2 fans, partly controlled by the computer, and with the switch in the head being a sort of "backup".

That is not necessarily an indication of "overheating". More often it's an indication of a radiator cap that won't hold pressure.

People have a HUGE misconception about the boiling point of water. They often think it boils at 212°, because that's what they learned in school. Well, that's only PARTIALLY true: they leave out certain critical details. Specifically, pure water at sea level pressure boils at 212°. Water with impurities, such as antifreeze, boils at a MUCH higher temp; and pressure GREATLY raises the boiling point also. The boiling point of a 60% water / 40% anti-freeze mixture is something like 230-240° at atmospheric pressure, and something like 260-270° at proper cooling system pressures of 15-18 psi.

The cooling fan in these cars COMES ON (IOW, in the factory's opinion, the car begins to need cooling at this temp, and not until it reaches it) at 235°. It shuts off (IOW, in the factory's opinion, no further need for cooling exists) at about 215°. 235° is just about the bottom of the red zone on the gauge, and 215° is about the middle mark on the gauge or maybe just below it. My car as an example, which seems to work right and has worked just like this for 20-some-odd years, will sit and idle; heat up until the gauge just touches the red; the fan will come on; the temp will go down over the course of about 2 minutes; the fan will shut off shortly after the gauge reaches the mid-point; the temp will begin to climb, over the course of about 3 minutes; the gauge will reach the red; the fan will come on; etc. etc. etc. It will sit there and do that for hours at a time, literally until it runs out of gas.

I'm telling you all this becuase nothing you have said, really is an indication of any kind of "overheating". Rather, it is an indication that the radiator cap is not holding pressure.

Change the rad carp, and make sure you have a mix of between 50/50 water/AF and 70/30; and try it again, except this time, watch it closely while it's idling. You might even want to go to the store and buy one of those cheeep little thermometers at the parts store that you use for AC repair, for about $3 or so, and duct-tape it to your upper rad hose, and see what the system temp actually is (since the gauge in the car isn't the most dependable thing in the world). Verify that the fan does, or doesn't, work, by the time the temp reaches 240° at the hose.

Jeff91RS

iTrader: (1)

thanks for the response
i guess i did leave some info out its a 91 tbi 305 l03 with about 135k. I am aware that the guage isnt perfect but it was pegged and the overflow tank was soft to touch (like if i wasnt afraid of being scalded by boiling glycerin i could have poked a hole in it with my finger) and this morning when i looked at it it was deformed and i will be picking up a new tank at the junkyard soon. I actually just got my stuff from moates.net today and i hooked up my laptop to play with the datalogging and i was watching temp and the cooling fan still didnt kick in. i think i traced problem to the relay (because i can jumper it and the fan kicks in and there are all the proper voltages at the plug) so i am awaiting my new relay should be in tomorow. I did check the old relay and it wouldnt click. Also i removed t stat and boiled it in some water and it opens at 192 so i put it back in. As far as the rad cap it is brand new (not to say its not bad of course) but i will look into that tomorrow

Jeff91RS

iTrader: (1)

so i have my laptop with winaldl running and i am watching my temp and it hits about 245 when i am sitting idleing and fan doesnt kick on. I am assuming that the ecu ,and by extension my laptop, are getting the reading off of the temp sensor by the t stat houseing. and that the guage gets the reading from the sensor on the side of the head, am i correct?