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Discussion Starter · #1 ·
Ok so this is my first post i have a 91 GMC K1500 ext 4x4 with a 5.7l v8 i replaced the motor last year after the head gasket went out and tore the motor down to find a dead piston and a cracked head i ended up putting a higher temp thermostadt in to keep it from overheating. Well the other day the wife was complaining about being cold with the heater on it wasnt blowing very warm air so i replaced the heater core but no luck i ended up putting a cheap thermostadt in again but now its overheating again while im driving down the road and stays really warm when im just sitting there. Im out of ideas. Any help would be awesome
 

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First welcome to the Club.

Have you checked the two hoses to the radiator? The top one is coolant to the radiator and the bottom is back to the engine. The best way to check is with an infrared thermometer but you can get an idea by feeling the hoses. The bottom hose should be cooler after the coolant passes through the radiator.

Make sure the radiator is clean from bugs and dirt. Air must pass freely through it and the AC condenser. The radiator core can plug up from gunk and rust. Just as air must flow through the fins coolant must flow through the core.

How old is the water pump? That's the heart of an engine. A plugged radiator or bad water pump could have caused overheating and resultant blown head gasket and cracked head. Either can do the same after the head and gasket were replaced. Check both to prevent another blown gasket and cracked head.

Ted
 

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Discussion Starter · #3 ·
Dont think its a cracked head or a head gasket im not smoking and theres nothing in my oil and im not buning it because im not replacing antifreeze the coolant seems to be cirvulating when i look at it with the radiator cap off
 

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I didn't say it was a cracked head or head gasket. I said a plugged radiator or bad water pump can cause overheating which can blow a head gasket and/or crack a head.

Ted
 
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Years ago with copper radiators you could have a shop rod out the core. They would remove the top and bottom and clean out the tubes with a rod.

Todays radiators are made of aluminum tubes and plastic reservoirs. Once they plug up there's not a whole lot you can do except replace it. But unless you know if it's plugged it might be a waste of money to replace it. If you can rig a water hose to seal in the top inlet you can check the flow that way.

Ted
 

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What XposTech said is important and are you sure it is overheating as you indicate coolant flow in the rad. This may sound silly but you did put the T stat in the correct direction right?
 

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Can i just blow it out with an air compressor and a blower nozzle?
I'm pretty sure you're talking about the fins. Yes you could clean the condenser and radiator with air but you stand a chance of bending over a lot of fins unless you keep the pressure kinda low. I've had good results with a garden hose like garagerog says. Just take care and let whatever cleaner you use work. 409 is pretty good. Spray it on a cold radiator from both sides and keep it wet for about 10-15 minutes. Then the hose spray to get everything out.

Ted
 

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I find this a very confusing thread, so I've stayed out of it until now.

Opening post;
-you put in a higher temp thermostat to keep it from overheating
-low heat from heater, you replaced t-stat with a cheap one and now it overheats

OK, how can increasing the temp rating of a t-stat the keep it from overheating?
Your description makes me think it had been overheating and you fixed it with the correct thermostat.

Ok, #2, your running cold, you change the t-stat and your overheating.

OK, #3, if your back to overheating and a good quality t-stat fixed it last time (my assumption at this point), why not try a good quality one again?

Anyway, the point I'm making is that your description points to the t-stat as your problen
 

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When you replaced the engine, did you replace the radiator? It sounds like the engine was replaced without diagnosing the cause of the failure and correcting it. Obviously, overheating would cause the head gasket, cracked head issue, but nothing was stated about repairs to the cooling system.
 
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