1979 240D temperature issue

[runbiodiesel]

Happy Holidays everyone,
Here's a real message about a Mercedes as opposed to more offers for
Prada, Rolexes and whatever!

My old 240 has developed an issue where its temperature goes up much
higher than it used to -- not overheating, but up to about 210 degrees
Fahrenheit or so at times, though sometimes it will go back to normal
at about 180. The system holds pressure just fine (no leaks) and the
coolant level is full. I tried replacing the thermostat but there was
no change.

I did discover the electric cooling fan is not working, though I don't
think it ever has (I ran 12V directly to it and no go so I assume the
motor is bad). Also, this happens even in cool weather at constant
speed so I doubt it would be caused by the fan not coming on.

Any thoughts on what to try next or suspicions as to what might be
wrong?

Also, anybody know where I can get just a motor for the cooling fan?

Thanks!
Steve

[t***@optonline.net]

Post by runbiodiesel
Happy Holidays everyone,
Here's a real message about a Mercedes as opposed to more offers for
Prada, Rolexes and whatever!
My old 240 has developed an issue where its temperature goes up much
higher than it used to -- not overheating, but up to about 210 degrees
Fahrenheit or so at times, though sometimes it will go back to normal
at about 180. The system holds pressure just fine (no leaks) and the
coolant level is full. I tried replacing the thermostat but there was
no change.
I did discover the electric cooling fan is not working, though I don't
think it ever has (I ran 12V directly to it and no go so I assume the
motor is bad). Also, this happens even in cool weather at constant
speed so I doubt it would be caused by the fan not coming on.
Any thoughts on what to try next or suspicions as to what might be
wrong?
Also, anybody know where I can get just a motor for the cooling fan?
Thanks!
Steve

Since it happens in cool weather, it's not the auxilliary cooling
fan. That
only comes on if either the coolant temp goes above a certain point,
or
the AC refrigerant at the receiver/dryer goes above a set point. At
least
that's how it's done on my 300SD, 116 series. Those conditions are
only
reached when its very hot, like 90 deg and you're stuck in traffic,
etc.

It's not worth screwing around trying to replace just the motor.
Fans, at
least for my car are readily available and not that expensive, ~100 I
bought
one on Ebay.

My suspicion would be a partially blocked radiator. How old is the
radiator?
I had the one go on my 300SD about a year ago. Started leaking and
looks
like it actually corroded from the outside in. There are no
aftermarket ones
available for my car anymore. Could get one from MB $800. I got the
old
one rebuilt at a local shop for $475. So, that's could be an option
if it comes
to that.

Another possibility is a hose that is partially collapsing when the
pump speeds
up.

[Cordy]

Post by runbiodiesel
Happy Holidays everyone,

Merry Xmas!

Post by runbiodiesel
My old 240 has developed an issue where its temperature goes up much
higher than it used to -- not overheating, but up to about 210 degrees
Fahrenheit or so at times, though sometimes it will go back to normal at
about 180. The system holds pressure just fine (no leaks) and the
coolant level is full. I tried replacing the thermostat but there was no
change.

What do you mean with thermostat? The temperature sensor or the automatic
valve that opens coolant flow once trespassed a temperature limit?
Usually I'd start from one of the two above. You could eventually
disassemble the valve and "boil it" on the kitchen with some water, to
see if it opens correctly, eventually checking with a thermometer the
temperature threshold. It's usually in 70-80° C. Let me say 165-170° F.

[t***@optonline.net]

Post by Cordy

Post by runbiodiesel
Happy Holidays everyone,

Merry Xmas!

Post by runbiodiesel
My old 240 has developed an issue where its temperature goes up much
higher than it used to -- not overheating, but up to about 210 degrees
Fahrenheit or so at times, though sometimes it will go back to normal at
about 180. The system holds pressure just fine (no leaks) and the
coolant level is full. I tried replacing the thermostat but there was no
change.

What do you mean with thermostat?

It's pretty clear that by thermostat he means the one in the coolant
flow path that every car has between radiator and engine. He said he
already replaced it and it hasn't fixed the problem.

Post by Cordy
The temperature sensor or the automatic
valve that opens coolant flow once trespassed a temperature limit?
Usually I'd start from one of the two above.

Two? What two? I have yet to see a car with a seperate temperature
sensor
and valve that controls coolant flow between the radiator and engine.
Might exist somewhere in a new car, but in his car, there is only one
thermostat and
it's a self-opening valve that responds to temperature.

Post by Cordy
You could eventually
disassemble the valve and "boil it" on the kitchen with some water, to
see if it opens correctly, eventually checking with a thermometer the
temperature threshold. It's usually in 70-80° C. Let me say 165-170° F.
--

I hope by "disassemble" you really mean remove.

Post by Cordy
Hi!
Stefano

[Cordy]

Post by t***@optonline.net
I hope by "disassemble" you really mean remove.

Of course.

Maybe you're overlooking I'm Italian. It's not very easy for me to find
the correct words in a different language, in a semantic space that I only
use here (mechanical English, I'd say mech-american English for the vast
majority of subscribers).
So, pardon me if I'm naive in my choice of words and grammar. I'm just
trying to help. My suggestion was on thermostatic valve, to be REMOVED
(ok...) and tested in a pot of boiling water, visually inspecting if it
opens totally. I can remember here a discussion a couple of years ago on
two different defective valves.

And then to carefully check if the instrument and the sensor of the
instrument work accurately.

[runbiodiesel]

Thanks for the input trader4 and Stefano. Yes, indeed I meant I had
replaced the mechanical thermostat that regulates coolant flow. I did
test the old one after replacement and it wors fine. Oh well, it's a
cheap fix.

Thanks for the advice abou the radiator. That makes sense. I found a
brand new radiator on e-bay for $99 and it just arrived today. When
the weather clears up a bit and I'm not contending with rain and mud
I'll try the swap and see if that does it. It makes sense. I'll repost
when I do and let you know how it goes.

While I'm at it, I'll see if I can find a cooling fan and replace that
too.

Post by Cordy

Post by t***@optonline.net
I hope by "disassemble" you really mean remove.

Of course.
Maybe you're overlooking I'm Italian. It's not very easy for me to find
the correct words in a different language, in a semantic space that I only
use here (mechanical English, I'd say mech-american English for the vast
majority of subscribers).
So, pardon me if I'm naive in my choice of words and grammar. I'm just
trying to help. My suggestion was on thermostatic valve, to be REMOVED
(ok...) and tested in a pot of boiling water, visually inspecting if it
opens totally. I can remember here a discussion a couple of years ago on
two different defective valves.
And then to carefully check if the instrument and the sensor of the
instrument work accurately.
--
Ciao!
Stefano

[t***@optonline.net]

Post by runbiodiesel
Thanks for the input trader4 and Stefano. Yes, indeed I meant I had
replaced the mechanical thermostat that regulates coolant flow. I did
test the old one after replacement and it wors fine. Oh well, it's a
cheap fix.
Thanks for the advice abou the radiator. That makes sense. I found a
brand new radiator on e-bay for $99 and it just arrived today. When
the weather clears up a bit and I'm not contending with rain and mud
I'll try the swap and see if that does it. It makes sense. I'll repost
when I do and let you know how it goes.

Ahye Karumba! $99? Amazing it's even available for a car that old.
Boy did you get lucky!

Post by runbiodiesel
While I'm at it, I'll see if I can find a cooling fan and replace that
too.

You should also verify that the circuit that energizes it works. On
my 300SD
there are two temp sensors, one in the engine coolant, other at the
receiver/
dryer for the AC. Either can turn it on via a relay.

Post by runbiodiesel

Post by Cordy

Post by t***@optonline.net
I hope by "disassemble" you really mean remove.

Of course.
Maybe you're overlooking I'm Italian. It's not very easy for me to find
the correct words in a different language, in a semantic space that I only
use here (mechanical English, I'd say mech-american English for the vast
majority of subscribers).
So, pardon me if I'm naive in my choice of words and grammar. I'm just
trying to help. My suggestion was on thermostatic valve, to be REMOVED
(ok...) and tested in a pot of boiling water, visually inspecting if it
opens totally. I can remember here a discussion a couple of years ago on
two different defective valves.
And then to carefully check if the instrument and the sensor of the
instrument work accurately.
--
Ciao!
Stefano- Hide quoted text -

- Show quoted text -

[Tiger]

I had similar issue with my old 380SE.

I changed the thermostat... no change
Changed the temperature semsor... no change.
Changed the radiator... no change.
Changed the fan clutch to newer type... no change.

Lastly, I had an issue with my odometer so I stuck in a different cluster
and to my shock... the temperature gauge registered normal... The conclusion
is that the temperature gauge does go bad that the reading is off... this is
probably due to some 'extra' resistance... in the circuit... wire
corrosion... etc. or the resistor on the termperature gauge going bad that
it reads higher temperature.

In any case, make sure all your hoses are new... after all the car is over
20 years old by now... so it is time to change all the heater hoses while
you are at it so it will last another 20 years... lol.

Happy holiday.

[runbiodiesel]

Thanks for the suggestion, Tiger. I can't believe I didn't think of
that since I had something similar happen on my sailboat which has an
old Perkins diesel. I went through all kinds of repairs before finding
out I had a bad gauge head (I had replaced the sender which made me
think the thing was reading correctly). Anyway, to finally test the
gauge theory I got an infrared temperature sensor that you just point
at a surface and click to get temp readings. Turns out when the gauge
was showing in the red the cylinder head temp held consistently at
about 180, just right.

I'll try the same thing on the car and see if I can rule that out.
Thanks again for the suggestion!

Post by Tiger
I had similar issue with my old 380SE.
I changed the thermostat... no change
Changed the temperature semsor... no change.
Changed the radiator... no change.
Changed the fan clutch to newer type... no change.
Lastly, I had an issue with my odometer so I stuck in a different cluster
and to my shock... the temperature gauge registered normal... The conclusion
is that the temperature gauge does go bad that the reading is off... this is
probably due to some 'extra' resistance... in the circuit... wire
corrosion... etc. or the resistor on the termperature gauge going bad that
it reads higher temperature.
In any case, make sure all your hoses are new... after all the car is over
20 years old by now... so it is time to change all the heater hoses while
you are at it so it will last another 20 years... lol.
Happy holiday.

[Tiger]

Yes, infrared thermometer is the best thing in this case... You should aim
at where the sensor is... and that is what the gauge should be reading. 180
degree is perfectly normal.

I remembered helping out another guy with 380SEL long ago... he did
everything like I did... replace this and that... but he had a machanic
suggestiing him to change this and that... costing him a fortune... I told
him to stop and change the cluster I had... and no more after that...
temperature is normal.

Make sure you aux fan is working... it is extremely important when running
AC... it would mean whether you really got AC or not.