Over heating.. I’m stumped!

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wavesillusion

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Recently started to restore my late father’s 1994 GMC 1500 5.0L 305 TBI. Had a battery draining issue with aftermarket alarm system. Had that removed starts up flawlessly.
Replaced all leaks as follows- water pump, thermostat, temperature sensor, radiator flush and all hoses replaced, manifold intake gasket. No leaks. Removed All air pockets in cooling system. Still running hot over 220. Any ideas for overheating?
 

evilunclegrimace

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Incorrect water pump rotation or incorrect intake manifold gaskets or gaskets installed backwards
 
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Schurkey

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1. What gauge is reading "220"; and is that gauge accurate? If the gauge is faulty, you may be chasing a problem that doesn't exist while ignoring one that does.

2. I don't trust current-production thermostats. I've seen too many that seem "sticky"; the engine gets too hot before the 'stat opens, then it goes too cool, then back to too hot, then too cool. Takes forever for the temperature to stabilize.

3. If the radiator is old, a "flush" is not likely to remove scale, or to reattach air fins that have corroded away from the coolant tubes. Radiator may need professional cleaning or replacement. Used to be that "radiator shops" were in every town even some small towns. Thanks to cheap Chinese radiators, those guys have largely gotten out of the business meaning that a professionally-cleaned, or re-cored radiator is not a viable proposition any more.

4. If the radiator can't heat-up the airflow passing through it, the fan clutch won't get hot enough to engage. Then guys install two or three fan clutches, giving up in disgust at the high number of "defective" fan clutches.

5. Every vehicle I've done radiator or A/C work to in the last number of years has had an ENORMOUS amount of dirt caught in the air fins of the radiator and the A/C condenser. I've blown amazing dust-clouds out of those heat exchangers using compressed air; it might be that a garden hose would clean 'em out also.

6. If you're going to flush the radiator, drop the coolant drainplugs on each side of the block. Kinda guessing you have a plain pipe-thread plug on the left side, and the knock sensor also plugging the coolant drain on the right side. Be sure to re-seal and properly-torque the plugs when reinstalled. There can be a lot of rust that sinks to the bottom of the water jacket.

7. MAYBE someone has replaced the block core plugs; or installed a block heater, and left the old core plugs inside the block which also can interfere with coolant flow.
 

GoToGuy

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An overlooked part of the service flush and fill, back blow all the crap out of the radiator fins. Remember the radiator is big metal screen constantly screening all the sand, small rocks, bees, moths, grass, flies, feathers, fuzz, road garbage. It all adds up and drops thermal efficiency. And a pigeon my wife hit and cooked into radiator. What a mess.
When removed and replaced the hoses, did you check the heater was flowing well? The water flows slowly through it so it tends to have debris fill it, reducing flow so it causes a low heat output. Using a hose to direct flush at heater inlet tubes can result in it blowing the sediment out. I had one blow a mud blob out like a connon ball. All the above good advice things to aware of. Good luck!
 

Erik the Awful

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Verify the coolant temperature. Then verify the temperature that the thermostat opens - or just replace it. Thermostats are cheap.

Still have the factory shrouds in place? They ensure the fan pulls air through the radiator. Without it you just recirculate hot air under the hood and don't draw anything through the radiator.
 

wavesillusion

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Verify the coolant temperature. Then verify the temperature that the thermostat opens - or just replace it. Thermostats are cheap.

Still have the factory shrouds in place? They ensure the fan pulls air through the radiator. Without it you just recirculate hot air under the hood and don't draw anything through the radiator.
ive replaced the thermostat and water heater. I'm not sure about fan shrouds. I'm planning on testing the temperature around the radiator.
 

Carlaisle

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Just because the thermostat is new does not mean it works. Pop the old one back in and see if the problem goes away.
 
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