Really weird noise

[J4GRAND]

Since winter is upon us full force I've had to use the "turkey cooker" i.e. heater in my truck quite a bit lately. When I shut the truck off, I hear this noise coming from the heater outlet (or somewhere in the center of the dash) that sounds like a bouncing, metal ball. It's very quiet and starts with a long duration rapping sound then the rapping gets progressively shorter until the sound disappears. Almost like the sensation of dropping a rubber ball on a floor from a height- the ball bounces high the 1st couple of times then bounces shorter with the passing of time.

I guess what my question is is this. Is there some sort of check valve in the heating system that would close upon the vacuum being removed with the shutting down of the engine? I have never heard anything like this and thought it was bizarre.

[janie]

Patrick:

If you would quit trying to cook Sumava fish in your rig, it would probably stop. (grin)

Anyway, back on topic. Peso does the same thing sometimes. I know, it does sound like a rapping noise.

Honestly, I think it's due to the metal expanding and contracting/heat/cold issue.

But I've been wrong before.

Janie

79 J-10 "Peso"
360 TH400
Rust...going away

[mtn goat]

I think what you may be experiencing is an air pocket in you heater core...this sounds like boiling/bubbling of the coolent when the water pump stops pushing. I have had this happen before and sounds exactly like you describe...may even be a pin hole in there somewhere letting air in but not bad enough to drip.

[PlumCrazy]

I agree with the Goat...sounds like air trapped in the line. We get the same thing with our water chillers at work...sounds like little man with hammer tapping.

[carrotman]

The heater and defroster are run by vacuum motors which control the airflow. The vacuum storage tank is on the firewall and may have a check valve that isn't working right,or you may have a leak in one of the hoses. If no vacuum leak and the heat and defrost are working, don't worry about it.

[Banks]

If you pull the defroster hoses off the houseing you WILL be suprised at the stuff you will find in there that has fallen down the defroster vents.

[J4GRAND]

I've had air trapped in the coolant system before and this is a totally different noise than that. In addition, this noise only lasts a few seconds. I'll try to describe what it sounds like.

Bonk......bonk.....bonk....bonk...bonk..bonk bonk bonk bonk.

Total time for the bonks 5-7 secs. The sound is definitely inside the cab. Have listened for it under the hood and you can't hear it. I'm looking at my parts catalog right now and I believe that it might be one of the "vacuum air valve actuators". As the vac bleeds off, it's opening and closing the valve.

[hippymill]

shoot the gremlin that is living under your dash!!! it will only cause more havoc if you don't kill it immediately!!!

[J4GRAND]

Being a pilot, I don't want to invoke the wrath of the gremlins.

"Gremlins! What's a gremlin?"

http://tesla.liketelevision.com/liketelevision/images/toonfest/lowrez/bugs4212.jpg

[mandoneer]

I dont know if the FSJ's have this but on the trucks that I have seen that have this type of issue, its the vacuum regulated flap that changes from Defrost to Vent , my friends chevy does the same thing execpt his is more like Flap Flap Flap Flap FlapfFlapFlap and after about 10 sec or so it stops

[Gawdzilla.]

hmm....rapid bonk bonk bonk coming from the dash of The S**T....dare I say it??

funny how it starred it out on the message but it doesn't do it to your sig. ??

[ January 16, 2004, 10:14 AM: Message edited by: Gawdzilla ]

[J4GRAND]

Hasn't been any bonking in the $LUT in a long time besides the heater noise. Maybe with the new g/f....

Mandoneer- I bet it is that valve in there. Heat and defrost work great so I'm not going to worry about it.

[Gawdzilla.]

smile.gif cab of a FSJ is always been my favorite spot to woo the ladies!