-89 chevy, 305 auto
-no problem until 2 days ago
-at a red light or going down the interstate with no throttle it starts climbing but get on the gas, and goes back to normal
-upper radiator hose is hot
-coolant level fine
-don't know the condition of radiator
-don't know the condition of thermo
-new cap (3 months)
-with cap off, get periodic gurgling out of radiator
-haven't checked to see if heater works when overheating
-no white smoke

Just wanted to get some senarios (sp?) and tap into ya'lls vast knowledge <IMG SRC="smilies/wink.gif" border="0"> before I started. I know the thermo and hoses should be replaced as a rule. Just really looking for theories. Any help is greatly appreciated.
Thanks
Adam

does it have a clutch fan? if so maybe its bad.

dave

Yeah, does have a clutch fan. Doesn't feel loose or wobble when you grab it. It turns freely with engine off. How do I tell if it's good/bad
Thanks

when it is overheating at an idle see if it is spinning.

dave

Originally posted by the reverend:
<STRONG>-89 chevy, 305 auto
-no problem until 2 days ago
-at a red light or going down the interstate with no throttle it starts climbing but get on the gas, and goes back to normal

-upper radiator hose is hot
-coolant level fine
-don't know the condition of radiator
-don't know the condition of thermo
-new cap (3 months)
-with cap off, get periodic gurgling out of radiator
-haven't checked to see if heater works when overheating
-no white smoke

Just wanted to get some senarios (sp?) and tap into ya'lls vast knowledge <IMG SRC="smilies/wink.gif" border="0"> before I started. I know the thermo and hoses should be replaced as a rule. Just really looking for theories. Any help is greatly appreciated.
Thanks
Adam</STRONG>

Could be the thermostat sticking just enough and the more pressure happens when you get on the gas opens it up. Check the fan cluch after warm up, two ways, see if a rubber hose will stop the fan <IMG SRC="smilies/eek.gif" border="0"> <IMG SRC="smilies/eek.gif" border="0"> or turn off the motor and see if the fan is tight to turn.

Run that heater to see if there is air in the lines that is causing the gurgle. You can get a test kit from Napa to check the antifreze for head gasket leak. Check the condition of the radiator, might be time for service.

Clutch fan, check it to see how much resistance it has when the engine is at normal op temp. Also check for vacuum leaks, a big leak will cause you to run lean, causing overheating. Check your timing. If none of that works, get your radiator flushed, and check water pump.

Thanks for the input guys. I read on another thread about the heater on/cap off thing and tried it. Before the heater was on the water level was a little low but nothing major and after I turned it on, it gurgled and spat then held almost 2 gallons of water <IMG SRC="smilies/eek.gif" border="0">! Took it out, up and down some steep grades, etc and temp didn't budge. I think someone once told me you're supposed to run water in the damn things, go figure.
Thanks again
Adam