Sound of water flowing when heat is turned on

[Drew99GT]

1994 Corolla; when I turn the heat on first thing in the morning, I hear coolant flowing through the heater core; this car has a mechanical external heater control valve. It's done this for a year now; previously I had never heard this noise when turning the heat on.

No leaks, no loss of coolant, and the heat works great.

Semi clogged heater core restricting flow creating noise? I'm stumped.

Thoughts? Thanks

 

[mclasser]

Air in the cooling system can cause that noise. Do you hear it more when accelerating?

 

[brentalan]

Must be some bubbles/air pockets in there. You might have a very small leak or maybe you just need to bleed the system.

 

[Tegger]

Originally Posted By: Drew99GT
no loss of coolant

Are you judging this by the contents of the expansion bottle, or by the contents of the radiator?

Gurgling from the heater core is a classic symptom of low-coolant.

 

[Superflop]

I have a 1994 jeep grand cherokee v8 (not listed in sig as its a snow pig). It does that noise every once in a while and ive even used a vacufill to make sure its full.

Edit: i didnt read the op post correctly. With the rad cap loose and the heater on full run the engine till its up to temp (tstat open). Check level. add if necessary. If possible mark the level of the tank and check periodically for loss.