Coolant through heater core noise

I bought a 96 3/4 ton 7.4, the intake had been done and it had been converted to green coolant. I have a few questions:

1-right after I got it both the front and rear heater cores went out. I replaced the cores and now when I start it I can hear the coolant circulating through the front core. When I idle then get on the gas a little you can hear the noise also. It is like there is air in the system and once the core fills the noise goes away. I have bled the system as best as I can, filled the radiator, filled the reservoir to the appropriate level. What should I do to fix this?

2-I am running into an over heating condition, this started after I replaced the heater cores. I have replaced the thermostat and fan clutch. When I am just running down the road it runs 200-215 as soon as I stop the temp shoots to 230. If I rev the engine it will come down. If I am pulling my trailer a 3000k boat and trailer on flat roads it will heat up to 240. I have not run it into the red but the temps scare the begeaus out of me. It acts like there is an air lock at the thermostat but I would think it should have heated up and opened by now. The temp does not rise faster than normal but after 20-30 miles of towing in D @ 60 the engine will get hotter than I like. I have verified that the aux fan is working, there is no white smoke, no coolant in the oil and there doesn't appear to be any excessive system pressure. I have replaced the radiator cap also. Head gaskets, raidiator ? ??

In the morning after it sits all night, where is the level of coolant in the overflow? It should be upto the "Cold" line.

How did you bleed it? My 96 Chevrolet car has a bleeder screw that needs to be cracked to bleed the system. I am not sure about the Vortec truck engines. Sometimes a vacuum pump can be used to get all the air out.

However, since you clearly have air in the system, the coolant should be checked for signs of exhaust gases.

The tstat should be inspected by droping it in boiling water to make sure it is opening properly. I know you replaced it but you should be sure it is working right.

Has the water pump ever been replaced? If the coolant checks out, you should make sure the pump is operating properly. The impellar could be worn and the system will overheat when under a load.

The lower rad hose has a spring inside it to keep the hose from collapsing. If you rev the engine, what the hose and make sure it does not collapse.

//2000CAYukon

I have not replaced the water pump yet, that comes tomorrow, I did not see a bleeder valve but will look again. When the engine is cold the reservoir is at the proper "cold" level. I don't see any bubbles in the radiator and it is a new radiator, I guess I better get a gas test kit.

I have not replaced the water pump yet, that comes tomorrow, I did not see a bleeder valve but will look again. When the engine is cold the reservoir is at the proper "cold" level. I don't see any bubbles in the radiator and it is a new radiator, I guess I better get a gas test kit.

YOU might as well change the thermostat while your doing this if you have not already done so.

sounds like you have air in the cooling system. After you install the water pump, fill the radiator about 1/2 way with coolant / water mix, turn on both heaters to full hot. Start engine and let it run with the radiator cap off. While engine running fill radiator to about 2 inches below the top.....let enging run at idle or a little faster until the thermostat kicks in. Continue to run engine after thermostat works...fill radiator up to close to the top and let run about 5 min or so like this, while montioring the level of fluid in the radiator...Keep radiator full....after some time...put cap on radiator and fully tighten. Fill overflow tank to the proper mark and drive it.

Running the ening with the radiator cap off allows you to get the air out of the system....I would do it for some time with a suburban with rear heat. Don't take the cap off the radiator unless the engine is fully cold and don't fill the radiator all the way to the top before the thermostat cycles or you will have a lot of overflow. ** Keep face away from directly over radiator opening and monitor the temp guage and the water level at all times.

Replaced the water pump and talked to a radiator guy who said that some of the after market heater cores don't have a flow restrictor in them to prevent the sounds I am hearing. Found out it won't hurt anything and means I have real good flow.

Last year I replaced the water pump in my '98 Sub. After that no heat out of the rear. Tore stuff apart in the rear. Thought I was going to have to replace the rear core. Could hear the same thing you're talking about. Turns out it was just air in the system. Park uphill one night and downhill the next. Took a week to bleed it out. Also the engine temp guage was fluctuating until the air got out of there. Hope this helps........Steve