chevy 2004 overheating
 

my blazer over heats at low speeds and cools down on the interstate checked the fan clutch its not that no milky oil no white exhaust no bubbles in the coolent a slight smell of antifreeze in the cab going too replace the thermostat tommorrow any ideas what else it could be

It actually does sound like the fan clutch and thermostat. If the fan clutch goes bad the thermal valve won’t engage at low speeds so the engine can only rely on you driving high speeds so the fan can turn faster to cool it off in combination with wind going through the grille.

thats my take on it because mine is overheating too. Difference is I’ve replaced the clutch, thermostat, water pump and bled the system and it’s still doing it....the coolant temp sensor only monitors temp in these blazer so It can’t be that and I’m not losing coolant at all.

I will replace the temp sensor and thermostat again though.

please update if you find anything new on your end

If you are smelling coolant in the cab, you must have a leak somewhere. Are you losing coolant?

If the leak is large enough, the cooling system would not be able to increase in pressure. This is important as at higher pressures the boiling point goes up. But if the boiling point cannot increase due to lack of pressurization, then you can get steam forming in the coolant passage-ways which would cause heat to stay in the engine due to steam not conducting heat nearly as well as liquid.

An easy and inexpensive thing to check is the radiator cap. If it is venting at too low of a pressure, then that could explain your symptoms; i.e. the boiling point would be reduced making cooling of the engine harder but not so bad that the extra cooling from going at highway speeds is enough to cool the system enough. Be sure to get the proper cap for your Blazer. Caps can be different depending on the way the overflow system is plumbed.

Another source of a leak could be the heater core or a pin-hole in a hose.

If it was not for the smell of coolant, I would have suggested focusing on the fan. You did not say how you checked the fan clutch. Are you confident in your check of it?

Another possible cause of overheating is if your fan shroud is not intact. Shrouds can make a big difference at low speeds.

BTW, changing out the thermostat is not a bad idea. It is inexpensive and not too hard to do.

P.S. I added punctuation to your post to help me make sure I was reading it correctly.

Also check for dirt, debris etc. in front and in the radiator. Also look for bent fins on front and back of radiator. We have seen this issue because of dirt and bent fins. A simple plastic bag on the front can cause this issue.

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Listen to what error401 said...i vacuumed out my radiator..and instantly noticed temps drop.
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