Heater Core?

2000 Dodge Ram 5.9 4x4. On initial startup or sitting for about 3-4 hours, I hear swooshing water sound coming from the Heater Core area. It is not leaking or the reservoir low on coolant. Could the heater core be going out? I am over due for a coolant flush. No fogging up the windows.

Sounds like a low coolant level to me and you are hearing the air pockets flow through the heater. Is your radiator full? Gene

The reservoir bucket is full but the radiator was a little low. I always check the reservoir bucket instead of the radiator. Need to check the radiator instead of the bucket for now on. Need to change coolant next week.

Might be a good idea to change the cap also... and make sure the line to the reserve/overflow tank is in good shape and well attached.

Normally, keeping the reserve tank full should get you a full radiator after a few heat/cool cycles. if the cap is bad or leak in the line, that may explain why radiator level was low.

Good idea.

Does it have AC? Could be water from the evap core not draining.Even when cool and running defrosters over 32 degrees the AC comes on with defrost.Rocky

Does have AC.

X2 on checking the overflow hose and rad cap. Pressure will push coolant out but when cools down vacuum pulls the coolant back to the radiator.

I have the same sound each time I start my 01 Cummins- and just been living with it. Will swap out the cap, check the rad level and go from there.

If the rad is low, it might be a good idea to pressure test the cooling system to find out why. You will want to fix a leak before you flush the system and add new antifreeze. Gene

I just drained the radiator and reservoir bucket and refilled it. Also changed the radiator cap. No more noise. If the radiator is low, shouldn't it pull coolant from the reservoir bucket?

It won't pull the coolant from the reservoir bucket back into the radiator if there is a leak in the system. The reservoir system relies on the vacuum the escaping coolant creates when it pushes the coolant into the reservoir, in order to pull it back into the radiator. A leak in the system bleeds off the vacuum before it can pull the coolant back into the radiator. Something as simple as the coolant in the reservoir tank being below the inlet from the radiator can result in not pulling the coolant back into the radiator.

The reservoir system is a great addition, but at least a few times a year I will pull the cap when the motor is cold to be sure the radiator is full. That is the result of an expensive lesson learned years ago. Gene

Thanks for the explanation.

When the truck is cold, the reservoir bucket is at the ADD mark. I took off the radiator cap and noticed that it is full. After driving the truck for awhile, the reservoir bucket is at the Full mark fully warmed up. When it is cold, is it suppose to be at the ADD mark? I hear no more swooshing water sound.

It would be "normal" for the mixture to be lower in the reservoir when the motor is cold and for it to be at the full line when the motor is at operating temp. Normal would be for the level to be at the add when cold, increase at a reasonable rate to the full line, and stay there until the motor is in the cooling down stage when the level should end up back at the low line it started from.

Of course, we are assuming when the mixture is at the "add" it is still covering the point where the coolant travels to and from the radiator. The reservoir doesn't say "add hot" or "don't add if between the add and the full lines" does it?

If the level is making abnormal swings or radical changes I would want to look into a bad thermostat or other cooling issues. Gene

The reservoir says Add and Full only. You could tell when the Thermostat kicks in. The gauge will read 200 and then it will lower when the thermostat opens. I'm thinking this is normal now. Will keep an eye on it.

air in system had the same odd sound i burped the system problem solved. at least it was for me.