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2003 Blazer S-10 moody heat

Generally have heat only when over 30 - 40 mph, though sometimes goes cold then back to hot even at 50 mph. Also, air only comes out of vents, not heat on floor, no matter where I put the dial. Lastly, check gage light just came on once while climbing a hill, and temp gage was redlined at 260. Finished climbing hill, temp went back down to about 200 before I could pull over. there was only cold air at the time.

That sounds like a water pump problem to me. Does your Blazer have a timing belt? If it has not been changed maybe now would be a good time and do the water pump at the same time.

Thanks for the suggestion. I’ve been out of touch since the ice storm in the NE last week, power out at work until Tue.

Actually, a mechanic reccomended I check the coolant level, that even a qt. down might affect this. I ADDED A GALLON ! PROBLEMS GONE ! Boy, I felt stupid, but glad that solved the problem.

A leaky intake manifold gasket caused the coolant level on my 2000 Blazer to start dropping slowing (~1 pint/month). You should keep an eye on the level and check the oil for any traces of coolant. I’m not sure if the 2003 Blazer had the improved gasket or not. Since the intake gasket was replaced in 2004 there has been no loss of coolant.

Ed B.