over heat question

[NYC-10]

my truck has always run at the correct temp but one day It just started to run hot.I changed the thermostat,and It would go all the way hot then back down.Tonight just went all the way to hot and stayed there,heater was blowing cold and rad hoses are pressurized.I also noticed upon startup there is a little rattle at the front of the motor but there is no coolant leaking out of the weep hole.I did a pressure test and it was fine.What do you think?

[Lugnut64052]

Temperature gauge reading hot and the heater blowing cold usually means you're low on water, or you have a big air bubble in the system. Crank it up and let it run with the radiator cap off. Let it puke out any air, then started adding coolant. Once it gets up to operating temp and has burped all the air out, and you've filled it back up with coolant, THEN put the cap on and test drive. Do all that with it running. May take you a while, like a half-hour.

[spinning wheels]

Originally Posted by NYC-10

my truck has always run at the correct temp but one day It just started to run hot.I changed the thermostat,and It would go all the way hot then back down.Tonight just went all the way to hot and stayed there,heater was blowing cold and rad hoses are pressurized.I also noticed upon startup there is a little rattle at the front of the motor but there is no coolant leaking out of the weep hole.I did a pressure test and it was fine.What do you think?

Your temp gauge could be on the brink. Looks like you have done some trouble shooting. If you can get a hold of a temp gun. That's one way to pin point troubled hot spots. The air bubble sounds like the most likely.

Good Luck, post your finding when you get it figured out.

[LMN8UR]

If you aren't getting hot coolant to the heater, and you don't have air in the system, I'd say it sounds like a flow problem.

[NYC-10]

This morning I ran the truck with the cap off,Had to add about a gallon of h20,it burped alot heater hoses are hot but lower rad hose is cold.Also,I do not see the coolant flowing in the radiator.Could the pump be bad without coolant leaking out the weep hole?I am stumped

[truckdude239]

yes it can

[Lugnut64052]

Originally Posted by NYC-10

This morning I ran the truck with the cap off,Had to add about a gallon of h20,it burped alot heater hoses are hot but lower rad hose is cold.Also,I do not see the coolant flowing in the radiator.Could the pump be bad without coolant leaking out the weep hole?I am stumped

I went back and read your original post along with this one. Kinda sounds like you got a bad, new, thermostat. I'm guessing it's stuck shut now.

I have seen a bad pump once or twice where all the fins were rotted off the impeller, but it's rare. Always was on a vehicle where the coolant looked like river mud.

If you grab hold of the fan can you rock it back and forth very far? Half inch or so is normal but if it flops back and forth a ways maybe your pump is bad. I think I'd slap another thermostat in it and do the run/puke/refill routine again.

[justtime520]

I had the same exact problem, the heater hoses hot and the radiator hoses warm/ cold. You have air in you system and its stuck. I let my truck cool down. and started her up. i then put gas half throttle. until it got warm. then i let it cool all the way down and started over again for several times. i did that for about an hour and leveled itself out. keep the radiator cap off for the hole time. You ran you radiator low forcing air in. I pushed on the gas to force the water pump to work harder. it worked fine and i hope it works for you.

[spinning wheels]

Originally Posted by NYC-10

This morning I ran the truck with the cap off,Had to add about a gallon of h20,it burped alot heater hoses are hot but lower rad hose is cold.Also,I do not see the coolant flowing in the radiator.Could the pump be bad without coolant leaking out the weep hole?I am stumped

Is your top radiator hose hot? Your bottom radiator should be cooler than the top radiator hose as the water has traveled thru the radiator at that point.

If your top radiator hose is hot, then you should be getting water thru your thermostat.

[NYC-10]

top hose was hot-when the thermostat opens should I be able to see the flow in the radiator,because I did not see any flow.

[spinning wheels]

Originally Posted by NYC-10

top hose was hot-when the thermostat opens should I be able to see the flow in the radiator,because I did not see any flow.

If you have water in your cooling system.... Yes you should be able to see it.
But it is possible that you have trapped air in your system.

If you can't see it flowing in your radiator, add some water until you see it cycling thru you cooling system. As long as your water pump is working, you should see it flowing thru your radiator.

If your radiator is topped off and you still don't see it flowing. I'm just throwing this out there. Could your radiator be clogged up?

[justtime520]

NYC i am sure you have air in you system. when i changed my radatior fluid and thermostat and water pump it did the exact same thing to me. Stressed me the hell out. But dont stress my friend, just make sure the radiator is full. keep cap off turn on the truck and hold down the gas until it gets about 10 degrees over normal temp and shut it down. then let it cool all the way down and repeat. After you do this several times you will notice that the temp will level out and be right where it needs to be. and when you look at the radiator you will be surprised that it needs more green juice. and dont be shy with the gas, rev that bad boy up until it gets hot. you gotta force that little bastard air bubble out. good luck my friend

[El Jay]

When I change a thermostat, I drill 4-6, 1/8" holes, in the "flange" so that any air in the block will be pushed through to the radiator.

Redneck, to be sure, but there ain't no "air lock" in the engine.