over cooling rodeo

I have a 97 rodeo with the 3.2 L dohc engine. It's over cooling when the tempture is cold outside and I'm on the highway going over 3000 rpm. The heater does'nt pump out any heat until I get off the highway. Any help will be appreciated.

Your thermostat is probably stuck open.

I changed the thermostat twice. I've also checked the temp rating of the antifreeze its good to about 20 belowDo you have any other suggestions?

is your fan clutch malfunctioning such that your fan is engaged all the time?

it will always be turning some, but not engaged so it is actually providing cooling air circulation until the temperature is hot enough.

do you know that kind of loud isuzu fan noise when it is engaged? do you have that even when it is cold?

otherwise, you're sure the themostat isn't installed upside down?

//bc

I had a mecanic do the second thermostat so Iam pretty shure thats not the problem.but I will check the fan clutch and see if that is the problem. Thank you for the idea.

ok, the other thing that just occured to me. did you use a oem dealer isuzu thermostat. there have been a number of posts indicating that non-isuzu thermostats can be problematic, especially if they are not the *exact* heat range.

general problems with the flow of your cooling system are also things to consider and rule out as you go, including a clogged or restricted radiator and and a clogged or restricted heater core. and finally, of course, the water pump operation. you pretty much have to tackle it one at a time and observe. without being there, i'm still leaning towards the thermostat....

//bc