Mercedes-Benz Forum banner

1 - 14 of 14 Posts

·
Premium Member
1998 SL600, 2015 GLK250, 2014 RAM1500 EcoDiesel
Joined
·
70 Posts
Discussion Starter #1
I'm scratching my head on this one. My vent line return hose had a crack in the fitting right at the expansion tank. left some residue on top the tank. So I replace the expasion tank and cap with new parts. I bled all the air out with the heater on hi. Even had the vent hose disconected to watch for air bubbles passing through when the thermostat opened. Put the hose back on and the cap go for a drive. Temperature is same as before about 90C on the gauge but even after a half hour drive I check the cap and absolutely no pressure. No level loss is observed in the expansion tank either.
So I am at a loss here. This should be simple? I still had good pressure with the old expansion tank even with the leak.
 

·
Registered
several
Joined
·
23 Posts
I would check to make sure that there isn't any hose that might be leaking or anything like that . If everything looks good then replace the cap and see what happens.
 

·
Premium Member
1998 SL600, 2015 GLK250, 2014 RAM1500 EcoDiesel
Joined
·
70 Posts
Discussion Starter #3
I have looked for leaks. None to be found. It's only two hoses to replace the expansion tank. Hate to think its the cap as it is brand new but it's a possibilty I will check out.
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,391 Posts
I'm scratching my head on this one. My vent line return hose had a crack in the fitting right at the expansion tank. left some residue on top the tank. So I replace the expasion tank and cap with new parts. I bled all the air out with the heater on hi. Even had the vent hose disconected to watch for air bubbles passing through when the thermostat opened. Put the hose back on and the cap go for a drive. Temperature is same as before about 90C on the gauge but even after a half hour drive I check the cap and absolutely no pressure. No level loss is observed in the expansion tank either.
So I am at a loss here. This should be simple? I still had good pressure with the old expansion tank even with the leak.
Fill up to the reservoir line, when engine is COLD.

Regards,
aam.
 

·
Premium Member
1998 SL600, 2015 GLK250, 2014 RAM1500 EcoDiesel
Joined
·
70 Posts
Discussion Starter #6
Hello sqaar please explain pump the hose to the water pump. I'm almost certain that all the air is out by watching the flow from the thermostat vent line which looks air free ( no bubbles). Expansion tank level is right on the mark when cold.
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,391 Posts
I'm leaning towards a bum cap.
In order to remove the air, there is NO NEED to remove the small hose.
That is why it is there.
Air from the stat. housing ends in the PRESSURE reservoir.
That is provided that the holes&hose are OPEN.... And the HEATER is ON.

If you fill it to the mark COLD, and the cap is good, as the coolant expends/HOT.
You GOT to have PRESSURE.

Now you either have a leak.
Or like Mr. Bunker said.
Your cap is BAD.

Is it like a thread, or like the old style?

CK the vent hose, by the cap.
You also have an extra NON PRESSURE reservoir.
(It is in the FENDER. )

It may be going in there, so you can't see it leak.....

Regards,
aam.
 

·
Registered
'06 E500, '99 ML430 & '07 SL65 AMG
Joined
·
648 Posts
Hello sqaar please explain pump the hose to the water pump. I'm almost certain that all the air is out by watching the flow from the thermostat vent line which looks air free ( no bubbles). Expansion tank level is right on the mark when cold.
If you have had all or a large portion of the coolant out then hand pumping the host between the radiator and water pump will help circulating the coolant in the system to remove the air if any.

However, even if you have air in the system, with the engine running it will eventually be removed. If you don't have pressure you have a leak somewhere.

if no coolant is leaking on the floor then as some suggested, it is most likely a defect cap.

Another thing you can try is to fill the coolant system to the brim with the engine cold. Yes the coolant will expand and you will get spillage, but it might help you see if you have a leak somewhere that normally is not below the coolant level. The engine will not get hurt by having the system overfilled but make sure no electrical and electronic is in the path of the coolant spilling over.
 

·
Premium Member
1998 SL600, 2015 GLK250, 2014 RAM1500 EcoDiesel
Joined
·
70 Posts
Discussion Starter #10
Sure enough got a new cap in yesterday and all is well. It's a first for me a new cap that was bum right from the start.
 

·
Registered
Departed 1998 SL500 (and the Pano is in Bogota)
Joined
·
11,121 Posts
Where did you get the first cap from and for how much ?
How about the second one that works ?
 

·
Premium Member
1998 SL600, 2015 GLK250, 2014 RAM1500 EcoDiesel
Joined
·
70 Posts
Discussion Starter #12
RKH first cap was a APA/URO for $14 second I got was a BLAU for $21 from AutoPartsWay.ca
 
1 - 14 of 14 Posts
Top