Coolant vent
 

Just replaced coolant (Benz coolant) on my 91 300E and thought I had everything in order. However, I guess I missed something. Now when I start the car and the climate control dial is set to 80 I hear sound of coolant gushing near the dashboard. The sound stops after a while (under one minute). This makes me think that I have air in the system.

I squeezed the hoses, left the radiator cap open while blasting the heater in full mode (the coolant does not seem to rise in the overfill tank while the overflow cap is open) and still I hear this gargling sound by the dashboard.

I read in the archives that there is a vent screw that also must be opened to allow air to escape while pouring the coolant. I can't seem to locate this vent. Can anyone point out its location. Also, why is the coolant level not rising in the overflow tank with the engine running and the heater in full blast mode. I hope that I have not screwed up.

The bleed ports are on the cylinder head just inboard of the dipstick handle. There will be 2 14mm head screws or a 14mm head screw and a temp vacuum switching valve.

Why should the coolant level rise because the heater is on?

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

[QUOTE]Originally posted by sixto
The bleed ports are on the cylinder head just inboard of the dipstick handle. There will be 2 14mm head screws or a 14mm head screw and a temp vacuum switching valve.

Sixto,
I have the same "noise" on my 260E ,1988, I have difficulties to understand the location you describe, have you any photo or drawing of that?

thanks for help

cc, check out this thread. It should be familiar. In fact the photo should be more than familiar :)

http://www.peachparts.com/shopforum/showthread.php?threadid=76198

The bleed port is just ahead of the temp switch valve in question.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Oh, I don't know why you're getting the gurgling sound.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

[QUOTE]Originally posted by sixto
[B]cc, check out this thread. It should be familiar. In fact the photo should be more than familiar :)

http://www.peachparts.com/shopforum/showthread.php?threadid=76198

The bleed port is just ahead of the temp switch valve in question.

Thanks for such a propt reply.
I hav eposted that image for another post.
I had my water pump replaced and there is some moise in the coolant.

Is the bleeding port the screw in the white circle in this image?

That's the one. There's a crush washer under the bolt that's easy to lose.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Thanks Sixto,

Sixto,
When I did the search on the archives I noticed that a few people had this gurgling sound when they turned on the heat. The most common explaination was that air in the syatem created that sound. As far as the coolant level rising should'nt it rise when the temperature gets hot especially when you have the resivor cap removed.

The coolant will expand when it gets hot. I misunderstood your question to suggest that it has something to do with the heater.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

So the question is why is it not rising when I have the cap removed and and I turn on the engine and let it idle for more than 10 min. Could it be because I have the heater on at full blast.

No idea. Sorry.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Sixto,
Thanks for your help. I found the bleed ports that you mentioned. Next time when I change the coolant I will remove the bleed ports and hopefully this will purge air in the system and the gargling sound will be gone.

Thanks

A Khan


You don't have to wait until the next coolant change to bleed air out of the system .... actually you should do it now.

It is best to do it when the coolant is warm but not hot for fear of getting burned by hot coolant.

Be aware of the advice regarding the washer underneath the bleed bolt, it easily gets dropped.

Haasman

I would not recommend opening the "vent screws". There is a vent line at the top of the thermostat cover that routes to the expansion tank, and any air in the system will eventually bleed, but it may take two or three cycles for the system to completely self-bleed.

Fill the system slowly and when it won't take anymore install the cap loosely and start the engine. Set the temp control at "max", to open the heater control valve, but leave the fan speed at low if you have a manually controlled fan. Observe coolant level as it comes up to temp. (It helps to block the throttle up to about 1200 revs.) The coolant level may rise before the thermostat opens, but once the thermostat opens the level will usually drop. Add more coolant as required to bring the level to near full.

At this point install the cap all the way and drive the car briskly for a couple of miles, then check coolant level and fill as necessary. At this point you're done, but check the coolant level after the next several cycles and fill to capacity as necessary. Also, during the next couple of cycles increase the temp setting to max for a while to ensure that the heater control valve opens so coolant flows through the heater core and purges any remaining air.

Duke