[W126 Coupe] 1985 500 a/c overheats

[Dick Spellman]

hi robert,

it's assumed that the correct 83C tstat was installed

what's the outside temp under the following conditions?
example 1, outside 90F.
example 2, outside 100F
example 3, outside 70F


what's the running temperature at highway speeds, no ac?
1. norm around 80-85C on the instrument dial
2. norm around 85-100 on the instrument dial
3. norm around 80 on the instrument dial

what's the running temp at stop n go speeds, no ac?
1. norm around 85-100 on the instrument dial
2. norm around 90-105 on the instrument dial
3. norm around 80 on the instrument dial

what's the temp when the expansion tank starts to gurgle and expel 
anti-freeze? if it's under 110C, have you renewed the expansion tank 
pressure cap with proper rated replacement?

does the overheating occur at highway speeds (what's the temp?)?  if 
yes, does the electric fan kick-on at or below 110C as it should? if 
not, fan control temp sender unit and/or electric fan need to be checked 
replaced.

if overheating at stop n go speeds (what's the temp?)?  if yes, has the 
visco clutch been checked and/or renewed?  if it's got 100k+ miles on it 
it's overdue for replacement

if all of the above check out then I'd test the radiator for internal 
blockage using an infra-red temp probe.  or just assume the radiator is 
garbage if more than 10 years old.

just my 2 as a non-mechanic who's worked through this stuff a few times.

dick

btb management wrote:

> My 1985 500 sec has been overheating after using the a/c for a short 

> time. 

> My mechanic has completed several fixes but  I can hear

> the antifreeze bubbling in the overrun tank and see leakage under the car

> whenever the a/c is run.  The thermostat has been replaced, a new 

> temperature gauge

> has been put in, as well as a few new hoses attached to the engine

> but the tank still bubbles everytime i run the a/c.

>

> any suggestions?

>

> robert

>

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