Coolant Noise

[bronyaur]

'99 Chevy K1500 5.7 ECSB (obs - not the Silverado)

 

A few weeks ago my radiator went south and I replaced it with one from Napa Auto Parts. The repair was straightforward with no issues. I changed the oil afterward and topped off the ATF. I've only driven the truck a few times since then (I use a motorcycle to commute). The last couple of times I've driven it I can hear a rushing water sound behind the glove box. It sloshes around corners and upon acceleration. Most of the time it sounds like shaking a plastic milk jug that's half full of water, but other times it sounds like it's water rushing through a pipe. There's nothing leaking and no coolant smell anywhere. The A/C, defroster, and heater are working fine.

 

Does anyone know what this is? The only thing I can think is that the heater core is going south, but what has happened that causes the noise I hear?

[5829BMG]

More than likely you have air trapped in the system. You can try running them system with the heater on and cap off to allow the air to purge. Also make sure the cap and recovery system is working properly.

[bronyaur]

I'll give that a try. Thanks.

[bronyaur]

Despite the recovery reservoir being full, the radiator was about 1/2 gallon low. I filled it and replaced the radiator cap. It's all quiet now. Glad that's all it was. Thanks.