No pressure in cooling

topliner

Member
Joined
Dec 25, 2009
Messages
31
Hi, I changed the thermostat on my car yesterday and renewed the coolant, I ran the car up to temprature initially the guage stayed at 80 degrees. I then took the car it for a drive and the guage showed mid way between 80 and 100 degrees, the heater is blowing hot air but what puzzles me is when the car is at normal temprature there is no pressure when undoing the radiator cap. I have since driven 200 miles with no signs of over heating or loss of coolant. The radiator cap was fine before the coolant change and the thermostat is a wahler bought from ECP with the identical mercedes part number on it.

As always I appreciate your help and advice.
 

brucemillar

MB Enthusiast
Joined
Nov 18, 2010
Messages
8,659
Location
Next Door to Alice - 25 'kin years now
Car
C55 AMG Wagon - W124 300te 4matic Wagon - BMW 4.8is X5 E53 - SWB Pajero 3.5 V6 24v
Is the stat the same temp rating as your old one?

You may simply have an air lock. Start the engine from cold with the coolant off the car. Get the front of the car as high as you can (use ramps if possible). Leave the car running for 45 minutes as idle with the ca still off. This should 'burp' any air in the system.

Do not be tempted to peek into the header or rad when doing this :^) It is at that precise moment that the car will burp and you will not find it funny.
 

RichardF

Active Member
Joined
Aug 24, 2013
Messages
548
Car
Sl 320
I'd change the rad cap.

The same happened to me. Just disturbing it may have finished off a degraded seal
 
OP
OP
T

topliner

Member
Joined
Dec 25, 2009
Messages
31
Hi and thanks for the replies,
the thermostat is the same rating as the old one, I will try the bleeding process as described.

The radiator cap is what I will try after I've rechecked there are no air locks.

It"s not over heating or boiling over.
 

LvR

Member
Joined
Apr 18, 2014
Messages
55
Location
South Africa
Car
A160 W168
Hi, I changed the thermostat on my car yesterday and renewed the coolant, I ran the car up to temprature initially the guage stayed at 80 degrees. I then took the car it for a drive and the guage showed mid way between 80 and 100 degrees, the heater is blowing hot air but what puzzles me is when the car is at normal temprature there is no pressure when undoing the radiator cap. I have since driven 200 miles with no signs of over heating or loss of coolant. The radiator cap was fine before the coolant change and the thermostat is a wahler bought from ECP with the identical mercedes part number on it.

As always I appreciate your help and advice.
Did you run it up to temp with the cap removed initially in order to check level constantly? ............... then I would say your experience is perfectly normal.

I would first allow the vehicle to cool completely with the cap off ........... check level and refill to correct level when still hot, then, with the cap still off again recheck and fill when cold. Fit cap when cold and drive till temp gauge shows normal operating temp.

Do not open expansion tank now .................. leave it to cool. When cold remove cap and check level ........... if normal fit the cap and repeat for a few days while thinking of flowers and beer and forgetting pressures
 
Last edited:

E55BOF

MB Enthusiast
SUPPORTER
Joined
Mar 11, 2013
Messages
6,654
Location
South Bucks
Car
S211 E500, SLK55, ML420 CDI, FJR1300, Caponord
What's the car? My R129 SL500 was exactly like that.
 

renault12ts

MB Club Veteran
Joined
Mar 5, 2009
Messages
16,212
Car
2005 W215 CL500.
Not at "80 to 100 degrees" it won't; especially if there's anti-freeze in the mix.
My point being that pressurised water boils at a higher temp.
 

LvR

Member
Joined
Apr 18, 2014
Messages
55
Location
South Africa
Car
A160 W168
My point being that pressurised water boils at a higher temp.
THIS! ............... and the converse is also true - iow - you cannot have the water in the expansion tank at any temp above the locale atmospheric boiling point of water if its not pressurized......... implication being with the cap off and the water not seen to be boiling, the water temp is obviously not anywhere near the boiling point of water at that geographic locale ........... water boils unpressurised at sea-level at 100C and way earlier the higher you are above sea-level - see Boiling Point of Water and Altitude

also

The radiator cap was fine before the coolant change....
As defined by what characteristics observed?
 

E55BOF

MB Enthusiast
SUPPORTER
Joined
Mar 11, 2013
Messages
6,654
Location
South Bucks
Car
S211 E500, SLK55, ML420 CDI, FJR1300, Caponord
As defined by not leaking, presumably...
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top Bottom