In an attempt to get my brother's car out of the garage, I need to figure out this problem. The car is overheating, and the fan is not coming on. Both radiator lines are cold, and there is a slight leak from the water neck gasket. The car is getting to 225F before we shut it down.  Does anyone have any advice?  

number one...    thermostats have wax pellets in them to force open the valve disc agenst the spring tention...   this happens when the wax gets to its designed temp..

when the engine overheats the stat goes wide open.. and the wax expands even more.. till it leaks out..   then there is not enough there to overcome the spring tention...

oh... and on vettes ... the fans do not come on till 228F..   another few seconds and you should have had fans..

the thermostat in that motor should be a 195F ... look at the bottom of the brass end of the stat.. it should have a stamping that says... 92C/195F  on it...  most of the time... the new numbered 195F degree thermostats  will have the last digit of the part number as a 9      (XXXX9)    

the spring with the brass bulb end that has the stamped in number goes into the motor...   not toward the radiator..  

please use antiseize on the threads...  its a buck in a little pouch next to the cash register at the chain parts store..  the bolts seize in the manifold way too much...

oh... and try not to buy the highest dollar superstats.. the inexpenive ones work fine.. sometimes better...     with a vette... you actually want to go to a gm dealer to get the exact stat.. it is a vette..    

oh.... and straight water will not work the thermostat..  the engine will boil over before the stat opens..   use at least 50 percent antifreeze...  or more ... not 50/50.. use straight..and dilute...  

i would also look at the temp with an infrared temp gun..  and see if the sending unit matches the gauge..  then look at the engine data... as the black and yellow coolant temp sensor wiring tells the computer to turn on the fan.(it also tells the computer how hot the coolant is to set fuel mixture).. there is sometimes a green wire over on the passenger side between the exhaust ports that is an override to the cooling fan relay...

one more thing...  the radiator caps have to hold pressure... if there is not any pressure.. the engine will overheat... steam bubbles will form... they will go up to the thermostat area...  steam bubbles will not transfer enough heat to the wax pellet to get it open the stat...  

Of course straight water will work the thermostat!  

straight water will not work a 195 degree stat in most cases...   it will turn to steam and push the coolant down away from it..  then there will not be enough thermal transfer to open the stat..

i am not saying that this will happen every time you use water... straight... but in my 30 years of being a professional mechanic ,,, water just won't cut it with a 195 stat...

putting a cooler stat in to a car with electric fans and fuel injection or feedback carbs will cause the ecm to force the fuel mixture rich to try to bring the temp up..   it will keep trying and trying.. and trying...   until the cats melt.. it will also send the fuel mileage through the floor...

remember the vette and a bunch of other motors are designed to turn on the fan at 228F..   that is when the ecm knows the motor is up to temp...

many other models of GM's use 215F and 223 F to turn on the fan...  

Straight water boils @ 212 at sea level with no pressure added, and at a lower temp @ higher altitudes. As long as the radiator pressure system is working properly the straight water will not boil until approx. 250 degrees. A 50/50 antifreeze mix will raise the BP.  

Thanks for the fan temp turn-on values. He is running a 50/50 mix, and the thermostat was a dud.  He is just concerned that 228 is just too high. Is there anyway to get the fan to turn on lower without a manual switch or putting it on the ignition?  

Look at the Hypertech coolant switch.  A little expensive and tricky to install though.  

that is the temp that the engine fans were programmed to turn on at...

if you run the engine cooler.. you will richen up the fuel mixture ...

there are companys who might be able to reprogram the ecm or the chip to run at a lower temp...  

Quick question. If the car over heats, do you need to replace the stat?  

in most cases i would....


the wax pellet under the rubber plunger end will continue expanding till it leaks out around the seal to escape into the cooling system...

when this happens .. there is not enough wax to push the pin out and force the disc open ... stats do have a strong spring...     i have not opened any stats after an overheat.. but i have found several with bits of wax hanging out around the pin.....

i wonder if the end of the pins can push through the rubber piston.....