Koda

Was inspired by the 455 overheat thread.

My 72 will gurgle some, for lack of a better word, when at idle, then when taking off, in the heater core circuit. It sounds a bit like rushing water, which it is, I suppose, then it stops I guess as the pressure tops out from the water pump turning faster.

I had some cooling issues a few years back, where putting a spring back in the lower hose and a higher flow thermostat helped, and I think all the air was not purged. But, I filled the radiator, let the thermostat open, and filled it more after level dropped. I've bled air a bit from a reverse flush kit connection on the heater hose by cracking it when it's hot and pressurized for a split second, so I don't think that lets air back in, and it generally puts out mostly coolant into the rag I hold around it.

The radiator and cap holds pressure enough that it has negative pressure when cold, enough that something equalizes when you open the radiator cap when cold to check level.

Thanks.

Fun71

A couple of thoughts:

Do you have an overflow reservoir or just an overflow tube? A reservoir should allow the air to be purged via normal driving and hot/cold cycling.

Do you have a vacuum actuated heater control valve? These have an orifice to restrict coolant flow; without it there can be a lot of water flow and a "rushing" sound. I experienced that when I installed a manual heater valve on my '70 way back in the dark ages.

Oldsmaniac

Your cooling system could be low.

Koda

Thanks for the responses.

Fun71: It's a 72 Chevy with the 350 and quadrajet. (I do own a 442, you guys are just more fun than the Chevites, so I ask advice for both here). Car is designed for tube, no overflow, but my grandfather added one and used non-stock cap. Cap on car is for a 75 Monte that came with overflow, got it new from dealer a couple years ago. So, I think the car is fully converted to overflow reservoir.

Secondly, it's a cable blend control, and a vacuum mode selector. Edit: You may mean the mode selector? That IS vacuum. It doesn't really make noise when changing selections, just at idle and off idle with the engine.

Oldsmaniac, I don't drive the car much, so I check fluids each time. Radiator, when cold, is flush with the bottom of the angled cap opening on the top of the radiator.

Other than a ticking from something which is on the to do list (worn rocker or tapping lifter or something) the car runs perfectly. This gurgling is just something it has done since I did the thermostat replacement a couple years ago. Did not do it previously.

Fun71

I meant the coolant flow control valve (heater valve) that fits on the passenger rear corner of the intake. AC cars have a vacuum controlled valve and non-AC cars have a plain hose nipple, but both have a 1/4" opening to restrict coolant flow through the heater core. Without this restriction the coolant can make a rushing sound.

Koda

Oh, that. Thanks, I need to check that out. It may be a bit, plus I believe that the Chevy plumbing doesn't go through the block, but I am sure that valve could be there.

Something definitely to check.

Car got 134a in 02, but the heater core I believe is original (evaporator is newer.)

Thanks.

rustyroger

If the car doesn't overheat or use coolant and you don't mind the sound I would leave it alone. Fixing it will involve a bit of work and if you DON'T hear the rushing sound on startup you have a warning your coolant level might be low.


Roger.

Koda

Good point, Roger. Just being fussy, I suppose.

JSPajak

Without the restriction in the heater hose fitting, the heater core will have a very short life due to the coolant flow surges. Ask me how I know...

Koda

That's a good point. I'll check it out next time I drive it. Since it didn't do this before I changed the thermostat and such, I am thinking that I just have an air bubble somewhere.