I have a 2000 Chevy Blazer 2WD, 2 door with A/C, Automatic trans. I have recently replaced the fan clutch, removed the thermostat, and flushed the system. The water pump was replaced with a new, not rebulit one about a year ago. I have no leaks that I can find. Engine runs great. Heater blows cold. It seems to heat up to about 230 degrees. I know it should run cooler than that. I am not a mechanic by any means. I was hoping someone might have a clue as to how to proceed to make it stop. It gets warmer going up hills and will cool back down to about 230 while descending the hill. Any ideas?

 

with your heater blowing cold it sounds like your cooling system is plugged up at the heater core. with the truck warmed up check both your lines running to the heater core. i am guessing one of the lines is hot and one stone cold. try flushing the lines if they are plugged up.

 

Yeah, I'd have to concur with warthogdriver. You'll want to backflush your heater core. Rather than explaining the process, I'll let a Youtube video do that for me:


That's pretty much what I do, except I use a homemade air chuck, made with some 1/4" pipe, threaded into a corresponding lever actuated valve, rather than mess with the vice grips, and I just use a hose clamp to secure it instead of screwing around with the electrical tape.

 

Although the heater core might be plugged I think it's more likely that some of the channels in your radiator are plugged....most often at the bottom. Crud sinks and eventually clogs those little slits. Normal flushing will not clear them and a chemical flush might not even do it. When your truck is hot turn off the engine and feel the radiator fins. If they are hot at the top and cool on the bottom then that's the problem. A couple of times I've been able to remove a radiator and tap it upside down to remove some crud but most of the time it's easier to just replace it. There's a bypass on the heater core so it shouldn't make the engine overheat. Proof...people clamp off the heater lines when they have a core leak.

 

^^^that could be it to. I know when my rad cracked i tore it apart .....full of mud looking sludge

 

I had similar trouble last year. I replaced my radiator after battling with it over heating issues due to its decade old age instead of wasting time and money on cleaners. The same gunk that was prevalent in my radiator was also gumming up my heater core. Your engine would run at normal temp with a new radiator, but still blow cold if the heater core was blocked. So sounds like a two step problem. The radiator is easier to access and replace, but the heater core is a pain to replace. The EricTheCarGuy vid posted above would help clear a heater core, however if its an exceptionally old and gummed up heater core I would be gentle with the pressure you put through it. The last thing you want is to blow a hole in your heater core and then have to contend with the smell of coolant till you work up the courage to replace it(i.e. happened to me).

In the long run, replace the radiator and be done with it if a flush with cleaner doesn't break anything loose. And be gentle with flushing your heater core or you will become an expert on how to remove your entire dashboard. Best of luck.