Gurgling (Rattle) Heater Core

Mark T · June 2, 2003

Hello All,

I have a nasty gurgle in my heater core 2000 GMC 2500, 92,000K.

I did seach previous postings with little or no info on the fix.

Anybody out there experince this problem and if so what did it set you back?

Thanks in advance.

cyclejerk · June 2, 2003

Try your search again, I know I read about a tech buliten on it. Air in the line/coil.

Mark T · June 2, 2003

I found a few fixes suggesting removing the filler cap on the coolant reservoir then idleing it hot several times in a row. Didn't work...

Another suggestion was to remove the heater hose and pick out a plastic restrictor?? Hmm, this sounds like a slight maybe, anyone heard of this before?

Shaners · June 3, 2003

I think MountaineerTom Had this problem on his '99. If I remember right though, I think you have already tried his fix...

Professor · June 3, 2003

I over-filled mine just below the hot mark when it was cold. After a couple of trips to work it cleared the air out of the heater core. Haven't heard it since then.

Wingnut · June 3, 2003

My 92 has been doing it for a couple of years now. I put a new radiator in it about a year ago...It got a lot quieter, but it still does it from time to time.

Z71GUY · June 3, 2003

I believe I have the same problem with mine. It only makes the noise when I am on the gas...usually when the engine is under high load and I am lugging it....

I tried Tom's fix and did not work...if anyone else has any ideas, please post them.

Thanks!

Eric

Zane · June 4, 2003

I had this problem on my 99 Zr2. Eventually the heater core clogged and left me without any heat in the middle of the winter!

I had to have the whole system flushed. Which, even at 50,000 miles, was good maintence.

Z71GUY · June 4, 2003

I had this problem on my 99 Zr2. Eventually the heater core clogged and left me without any heat in the middle of the winter!

I had to have the whole system flushed. Which, even at 50,000 miles, was good maintence.

Looks like this will be my next idea...

I'm pretty sure its the same noise you guys are talking about... comes from the center part of my dash (deep inside) near the light sensor for auto headlamps...

its very loud when I am under load luggin along at low RPM's... kinda like a rattle...I guess it could sound like a gurgle too...

Wingnut · June 4, 2003

Yeah, thats what mine sounds like...

Looks like a flush is in order.

Nice avatar Z71GUY.

MountaineerTom · June 4, 2003

BTW, here's the steps I followed;

-----

Get a jug of DEXCOOL (Havoline brand is GM approved).

Park on level ground.

The engine needs to be cool, or just slightly warm is fine too.

Add fluid in the surge tank until the level is slightly above the split line on the tank (an inch or so).

Put cap back on loosely, don't allow it to build pressure.

Start engine and let it idle for a minute.

Then, cycle the engine from idle to 3000rpm in 30 second intervals untill the engine coolant reaches operating temp and the thermostat opens.

Shut off engine and remove the cap.

Start engine and let it idle for a minute. Fill the tank to 1/2 inch above the "Cold Full" mark on the tank & put cap back on loosely.

Cycle the engine like before and wait for the thermostat to open again, then shut off the engine.

Put more fluid in if necessary, the fluid should be a half-inch or so above the Cold Full mark.

Mark T · June 5, 2003

Tried Mountaneer Toms fix again.

The gurgle quieted down considerably but came back.

I have a feeling it might be as simple as the surge tank cap. Doesn't this cap stop air from going out but allow air to go in for cooling? If so this is doing what Tom suggests above on it's own?

The breather on the cap itself might be plugged.

Mark T · June 8, 2003

I fixed it, the gurgling rattle is gone...

I disconected the return heater hose at the bottom end then cut in a radiator flush kit fitting near the heater core on the flow to side.

Then I placed the garden hose in the bottom end of the return hose and turned it on full blast for a good five miinutes. This created a back flush through the heater core, then reversed this set up and flushed the heater core for another five minutes going the normal direction. Place a green garbage bag over your Coil Line up, water hits the bag and runs off without soaking all the coils and plugs.

Since all was apart I flushed the rad and then put everything back together and replaced the Dex-Cool coolant. 50/50 mix

Needed to top up the surge tank once the next day and my coolant is about 3/4" above the cold mark when cold.

First run out, the noise was barely there (Huge Difference), the next day after topping up coolant the noise is gone.

I also replaced my Surge cap just in case this was part of the problem, Napa has them for $12.00. Not sure if this was nessasary but for $12.00 I did it to be sure.

Mechanic told me I needed a new heater core ($650+), sure glad I tried this first.

bigtruck21 · June 9, 2003

thanks for the tip

Z71GUY · June 27, 2003

Mark T, I'm glad to hear your results. I just tried Tom's suggestion again...I think it worked a little bit...the noise didnt come back until I drove it for awhile and the truck got nice and warm.

Would it be possible for you to explain or show what hoses you connected/disconnected? I've never flushed a system before...just drained and refilled on my old beater cars back in the day...so I'm kinda confused as to which hoses your talking about.

thanks!!