Classic Classic - 300tdi - auto. Gurgling noise from behind the dash

Hi all,

I'm still getting to know my 1995 300 tdi auto classic. I have noticed that when starting from a cold engine on occasion when I accelerate there is a strange gurgling noise that seems to be coming from behind the dash board.
I wondered if it could be coolant (but it does not seem to loose any or overheat at all). I also wondered if it could be transmission fluid.

Once warmed up, it doesn't seem to make it any more.
Any ideas?

David

My bet would be the coolant.
It could have trapped air inside.
You checked the oil cap on the engine for mayonnaise?
Around the top of the dipstick?
Any breather pipes from a rocker cover or crankcase for mayonnaise.
Or.... Has it had any work done on the coolant system?

Hi Mark and all,
No mayonnaise at all. I did change out the expansion tank a week or so ago (a small leak) but it was gurgling before then.
Is there any special procedure for bleeding out trapped air from the coolant?
David

Air trapped in the heater matrix, there is a simple procedure when refilling the coolant with the 300 tdi engine and it’s s stated in various work shop manuals and a few times in the Forums. Filling slowly from the top of the rad and waiting for coolant to appear at the thermostat with the bleed plug removed, then replacing the plug and topping up rad, the exact wording can be found in the Forum if u do a Search.





Sent from my iPad on a train

The heater matrix is in the dash it's connected to the coolant system.

Any news @DavidRRC ?

Hi Mark and all,
I have topped up the radiator and the thermostat and I think it is a little better, though there is still a bit of gurgling. I can't really tell if there was trapped air in there as I removed the Radiator plug while the top was off the expansion tank, and hence the radiator level dropped as soon as the plug was removed and air could get in to let coolant back to the expansion tank.
Perhaps a repetitive process. I see on the side of the thermostat housing there looks to be a bleed point. I wonder if it would be a good idea to just crack this open a bit while the system has pressurised and see if a little more air comes out. I'll keep experimenting. But air in the cooling system seems to be the source of the noise.
David

You need to fill the expansion tank to the correct level and replace the cap tightly then remove the bung from top of thermostat housing and fill it till full and then replace the bung its the only way to get the system full properly.

With my P38 I park it on a brick, on a slope so the expansion tank is highest point then top it up on level ground after. Little different for you but same principle as they are also terrible for trapping air in system.

DavidRRC said:

Hi Mark and all,
I have topped up the radiator and the thermostat and I think it is a little better, though there is still a bit of gurgling. I can't really tell if there was trapped air in there as I removed the Radiator plug while the top was off the expansion tank, and hence the radiator level dropped as soon as the plug was removed and air could get in to let coolant back to the expansion tank.
Perhaps a repetitive process. I see on the side of the thermostat housing there looks to be a bleed point. I wonder if it would be a good idea to just crack this open a bit while the system has pressurised and see if a little more air comes out. I'll keep experimenting. But air in the cooling system seems to be the source of the noise.
David

Click to expand...

When the air is in the heater matrix, that the highest point of the system and unlike a central heating rad the matrix doesn’t have a bleed valve, all your doing is carrying tout he method of bleeding the engine block and pipe work under the bonnet.
To remove the air out of the matrix u will have to drain the system completely, then refill the system slowly so the matrix will fill from the bottom pushing air out of it on the way, then using the method that has be stated above.. exactly, therefore the system under the bonnet is vented.
Any air that isn’t trapped can vent via the reservoir cap that’s why it has two valves, and you sometimes may find that later the need for topping up with a small amount of coolant when the engine has cooled.

As a side, why do you think the matrix has trapped are, have u replaced the coolant recently, when it is removed but later returns it is a system on bigger problems, iffy head gasket for example.

discool said:

To remove the air out of the matrix u will have to drain the system completely, then refill the system slowly so the matrix will fill from the bottom pushing air out of it on the way, then using the method that has be stated above.. exactly, therefore the system under the bonnet is vented.

Click to expand...

THIS!!!!!