Thermostat stuck open
 

I think my thermostat is stuck open. I live in Phoenix and when it cools down the check engine light pops on and reads coolant when I plug it in. When it hot out the light shuts off. Anybody ever change the thermostat? If so should I install OEM, replace gasket, do I need to drain coolant?

I havent replaced one on the hummer, but its pretty straight forward. Just go buy a new one and ask the guy at the counter if you need anything else. No need to drain the coolant. You might spill a little on the ground but it wont be much. Pull upper radiator hose (should be on the water pump) and pull out the thermostat, put new one in and replace hose.

Really easy, shouldn't need anything aside from the thermo, but ask anyways I too haven't done an H3, and be sure to do it when the rad and engine are cold. ;)

Also, Im not sure why the light comes on. Could be a low coolant problem, or something fancy like its beginning to take on a charge. In that case you would have to change it. If you have a volt meter, pull the radiator cap off, put your negative lead (of the volt meter) on the negative of the battery, then put the positive lead in the coolant (careful not to touch the radiator, just the fluid). If it shows a charge greater than .25 volts it needs to be changed. Let us know what you fing out.

I just did a coolant flush to see if thatwould help and it didn't. Can buy thermostat at auto zone or goto GM?

im curious about the science behind the voltage reading in the "coolant". type of meter,from the batt neg? who said?

Tom. Its just a fact. Not sure how to respond to the rest of your post. Complete sentences may help me out.

im curious about the science behind the voltage reading in the "coolant".


lets just stay here.

what creates the voltage?

is the voltage dependent on the meter sensitivity?

what is significant about .25v as opposed to .2v or .4 v?

is this test based on some engineering standard?

which standard is it based on?



btw,," Not sure how to respond to the rest of your post." is not a complete sentence!!

lots of jibberish here
 

sometime i believe what i read,,,then later i check the book.

compared to cars we worked on in the past,changing the thermo on th h3 is just short of a nightmare!!

yes you drain the system!.
no its not on top!
yes you pull the wheel house .

the thermo is below , rear of the starter, lower hose.

oh my i hope i never need to do it,,when its 5 degrees out!!


and btw the book says nothing about measuring the coolant "voltage"!

Over time the additives in the coolant deplete. Any time you have fluid moving through dissimilar metals there is a chance it can obtain a charge. The term is called electrolysis. The electrolysis can actually pit the metal in the coolant system. There is not a set "standard" that I know of, some say anything over .20 volts is bad, others say higher. Google coolant system electrolysis, and maybe something will pop up. I was only trying to give the original poster another avenue to look at, while he has attempting to find the cause of his DIC light. Sometimes you just have to throw the book out and learn from the guys with the dirty hands.