i've got a problem with my 2003 4.6L 2whl drv blazer overheating very fast.
I'm loosing coolint, when im in stop and go traffic the temp goes all the way then as soon as i get going on the high way it was go back to normal operating range, and advise and help would be great.

 

id change the thermostat first, pretty cheap insurance. but the fact that you say it cools fine when you get up to speed makes me think water pump.

 

yeah thats what the plan was thermo first then then pump if thermo failed. I've heard replacing the thermo can be easy, no clue about the water pump. can you suggest a reliable source for thermo replacement instructions.

 

ya thermo is a piece of cake. water pump really isnt bad either. just a little more time consuming. lol you have already found the most reliable source, blazerforum. if you use the search button ^ you can find just about anything you could want to know about your truck.

 

Could be air in the system.

 

Ditto on everything said. First check and see if you have a low coolant level. If you have coolant check for air in the system then go from there with your original plan.

 

Don't overlook the simple stuff. Along with a thermostat change, install a new radiator cap. If the system isn't holding pressure at 16psi, the coolant can push out of the system, boil off, and cause all sorts of issues. The cap is what is responsible for maintaining 16psi in the system.

 

I replaced the cap on mine because I am adding dexcool every 3 weeks. I have checked the oil and transmission for sign of leakage but haven't found any. I have pressure tested and do loose pressure quickly.

 

Same issue as sdt83 a while back. Changed the stat and water pump about four or five months ago. Have not changed the radiator cap though. Still I have some coolant leakage running to my starter when started in the morning, after a long commute it leaks a little when shut off. I have no clue where the leak is coming from.

 

Check your intake manifold gasket. I know that sounds strange for a coolant leak. Look around the valve cover on the right side (especially since you have coolant on the starter). Use a flash light and look around the back side of the motor and intake near the fire wall.

Also double check all the hose clamps to the stat and water pump.