Heater Core "Waterfall" sound on start-up

[RDN]

I've got a puzzling issue:

1995 3100 V6, on cold start-up I just started getting the "waterfall" sound from the heater core.

Heater core is fairly new, replaced ~4 months ago. Bled system then, the waterfall sound is recent (last month or so), and seems to be increasing. Sound goes away before the car warms up.

Engine uses little/no coolant. LIM is < 1 year old, and the system holds pressure well. Car passes emissions test easily, and no water vapor etc coming from the exhaust. Plenty of heat from heater as well.

I'm going to try re-bleeding the system, any other suggestions?

Ron

[rixGAphx]

1995 3100 V6, on cold start-up I just started getting the "waterfall" sound from the heater core.

Heater core is fairly new, replaced ~4 months ago. Bled system then, the waterfall sound is recent (last month or so), and seems to be increasing.

I'm going to try re-bleeding the system, any other suggestions?Nope, that's the ticket.

Re-bleed, TWICE.

After the first 'bleed', there's still air trapped in the high parts of the radiator (notice the hose arrangement, that prevents air from escaping during the 'normal' bleed procedure.
So you must get the engine up to operating temperature so the t-stat opens.
Coolant will then circulate thru the rad, and transport the rad's air to the LIM.
Allow the engine to cool.
The LIM will transfer that air to the bleed screw, via the little tube from the t-stat housing to the bleed screw 'tower', whence it can escape.

Some pre-'96 GA's had both a pressure cap on the reservoir, and a radiator cap on the rad itself.
If your GA has this, then you can bleed the air from the rad first, then bleed the air from the engine.
That will obviate the need for the second bleed.

Another possibility is a faulty pressure cap sealing washer.
If faulty, it not only allows water to escape as vapor, but allows air to enter as the coolant cools and shrinks, creating a 'vacuum'.
Check the pressure-holding capacity of the reservoir cap (and rad cap if you have one).
Most AutoZones have a 'Coolant System Pressure Test Kit' available for 'free' rental.

Only tighten the reservoir pressure cap as much as an average woman can easily do one-handed.
That's tight enough to seal against the 14-15 psi pressure, without being so tight as to distort or damage the delicate rubber sealing washer.

Hope this helps,
-Rick

[RDN]

Thanks Rick; I'll try re-bleeding the system tonight. As its a '95, I only have the cap on the plastic reservior - nothing but hoses on the radiator. By the way, the cap is also fairly new; its still possible that is causing the problem; this did not happen with the old cap.

I'll bleed it through the bleeder screw near the water pump. As others have discovered, it breaks off easily (ask me how I know). But GM sells just the bleeder assembly, so its an easy fix. And the new one only takes a screwdriver, so its less likely to be over-torqued.

As an aside, the system uses a 15psi cap, and that is what is on there. I have a new GM 18psi cap for a newer Grand Am; any harm in putting that one on?

Ron

[rixGAphx]

As an aside, the system uses a 15psi cap, and that is what is on there. I have a new GM 18psi cap for a newer Grand Am; any harm in putting that one on?Not if you don't mind your old, weaker, plastic-tanked heater core rupturing from the additional 3 psi.

Or LIM gasket, or hoses, or whatever is the weakest link.

The only BENEFIT of a higher pressure system is that it can run hotter.
specifically, an additional 3 degrees F of temperature before boilover, for evey 1 psi of preeure increase.

Now, you say your engine never gets as high as 212 + 45 (being 3 x 15 psi) = 257.
True, it doesn't.
But localized 'hot spots' in the cylinderheads, right next to the exhaust valves, DO get that hot.
And they cause localized boiling of the coolant at 258, creating a barrier of vaporized water (steam) that then prevents good heat-transfer and cooling.

Further, there's a 'heat-sink' phenomenon when you shut-off the engine, after running hard: The 'latent heat' in these zones isn't being removed by flowing coolant, so the temperature really rises and the liquid flashes into steam.
The great pressure then forces liquid thru the radiator and back thru the waterpump, and it gushes-out at the pressure cap.

My guess is that the newer engines were designed with the higher pressure to prevent these 'steam bubbles' from forming under the most extreme conditions.
But the engineers sure would have tested the other components of the system to make sure they could endure the pressure, and mebbe beefed-up some of them.
I wouldn't take the chance.

If you know what you're doing when bleeding, you don't need the stoopid 2-part bleeder screw.
Any old bolt will do, as long as you NEVER try bleeding 'hot'; only do it with the pressure cap removed.
Use some teflon tape to prevent rusting of the bolt to the tower, and a washer and fiber washer to make a tight seal.
Though if teh dealer has a cheap replacement with a slotted screw for a reasonable price, I'd prolly go for it.

Good luck,
-Rick

[mrcaddy]

Is there the same bleeder valve on the 4 cyl? I need to get a handle on this!

[rixGAphx]

The 4-cyls have no bleeder, because they don't need one.

The V6's have the intake manifold high above the heads, and water flows thru there; that's where air gets trapped.

No part of the 4-cyl engine's water jackets is above the radiator hoses, so no air bubble can become trapped high in the engine.

You can, however, get air trapped in the radiator when you fill the reservoir, since both hoses are located about halfway up the radiator sidetanks.
So run the engine up t operating temp and the t-stat will open, allowing liquid to flow thru the rad and push the air bubble into the 'Y' hose and thus into the reservoir.
Then refill the reservoir when it cools.