1988 Chevy Blazer Overheating after waterpump replacement

1988 CHEVROLET BLAZER
165,000 MILES • 4 CYL • 4WD • AUTOMATIC
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ROAE22
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Ive had a water pump leak for quite some time. yesterday it finally went out started overheating at a stoplight.. temp went from 210(norm) to 260 in seconds.. I bought a new waterpump, thermostat and bolts and installed... added new coolant to 3 1/4gal. warmed up just fine turned off turned on again was fine. let it run till it hit 210 (w/ heater on) temp kept rising slowly above 210. turned heater off, temp went down below 210 then slowly started rising again above 210 again.. i can't figure out what is causing it to overheat.. thanks
Apr 11, 2010 at 4:39 PM
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2CARPRO JACK
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An 88? is this a 2.5L? If so you can try the thermostat first, to see if maybe it is sticking.Those engines had a little bit of an issue with cracking the cylinder heads when they were overheated.If the t-stat doesnt do it, have a shop chemical test the cooling system for exhaust gasses, which is asign of a blown headgasket.The chemical test isnt 100%, but it is a real good indicator
Apr 11, 2010 at 6:27 PM
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ROAE22
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it is the v6 4.3... i just put a brand new fail safe thermostat in.. tested the coolant its clean.. head gasket was just replaced back in dec...
Apr 11, 2010 at 6:51 PM
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2CARPRO JACK
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Could be aflow problem.is theupper hose getting real hot? the lower should be cooler.Can you see into the radiator to verify if it has any build up that is restricting the coolant flow?.Is there anything clogging the radiator fins or blocking the air flow across it? Does the fan clutch lock up and pull more air when it gets hot?
Apr 11, 2010 at 6:56 PM
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ROAE22
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Yes the upper hose is getting really really hot...don't see a whole lot of gunk int he radiator but i also have not done a flush yet. fan is free moving and good and the radiator has no debre around it..
Apr 11, 2010 at 7:04 PM
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2CARPRO JACK
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The fan shouldnt be free moving when the engine is hot. It should lock up tighter as the engine gets hotter so it draws more air through the radiator.If this isnt happening, the fan clutch may be bad.If you drive it will it stay cool? (air moving across the front of the vehicle) Or if you hold the engine rpms up will it cool down? It should run right at 210 all of the time
Apr 11, 2010 at 7:12 PM
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ROAE22
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well the fan seems to be working fine... when i drive it w/ the heater on it heats up a lot quicker and goes way past 210.. if i drive w/out the heater on it stays around 210 sometimes going above 210... normally it sits just under 210 till the water pump went out yesterday.
Apr 11, 2010 at 7:22 PM
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2CARPRO JACK
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Sounds like either a flow issue or bad head gasket.May want to try having the radiator flushed/flow checked.I realize you had the heads done recently, but overheating can cause them to fail again. If thewater pump is new and the correct one for your year vehicle and the t-stat is good, the radiator cap or a flow issue are all that is left.
Apr 11, 2010 at 7:34 PM
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ROAE22
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ok thanks for the info
Apr 11, 2010 at 7:48 PM
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2CARPRO JACK
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Let me know what you find
Apr 11, 2010 at 7:55 PM