Having trouble with my 300SE
A bit of history
I did have a couple of small rad leaks. I noticed a kind of acrid
smell (hot antifreeze) around the front of the car after driving. On
investigation I found some damp patches on the rad.
I used (rightly or wrongly) a proprietory rad/leak sealer that is
applied to the coolant. This seemed to get rid of the dampness and for
a while it seemed, the smell. I drained some coolant out of the heater
supply pipe and pre-mixed this agent with this coolant and then
replaced it into the header tank.
If I drive along the road, all is ok (as far as I can tell).
As soon as I have to stop, the temp gauge starts to climb. I haven't
reached the red yet, but I know it would do if I didn't get the air
flowing again through the rad.
I managed to get the car home and as I manouvred in, the gauge was
rising. I quickly turned off and opened the hood.
I once again have a burning smell, but I can't see any leaks from
Also I notice I have no pressure in the coolant pipes.
I realise that I should change the rad, thermostat, temp senser (and
also the water pump, which I beleive is making a slight mechanical
Where is the pressure?. Have I a cylinder head problem?
Any suggestions as to a difinitive check to diagnose my problem.
Anyway, it looks like cooling capacity is reduced.
This is normal when radiator gets old. Partly due to reduced flow
through the radiator and partly due to corrosion of the cooling fins of
The fact that i was leaking could indicate some corrosion and the
sealer would in any case reduce the flow somewhat.
The temperature normally raises slightly when car is stopped until the
electric fan starts and prevents further incrase.
As long as the fan can keep the temperature from increasing futher, you
can continue without problems, otherwise you should replace the
Mayby you should do that in any case, since it has already shown sign
of weakness. Next time it breaks Murphy's law says that this will
happen when most unconvenient (and when you blame yourself for having
spared that cost).
Rob. Smith wrote:
Rob my Man,
How about starting with a new radiator cap?
That should hold the pressure.
Then I'd check why the fan and aux electric fan isn't effective.
Leaks aside, radiator is OK if no heating at speed.
But be forgiving, this old car isn't used to such high ambient temps!
Right on the ball as always. I'd forgot about the cap.
The fifth element!
To check this out (and not having a new cap to hand), I have firstly
cleaned the cap (inc the small reverse pressure release in the
centre). I have now pressurised the system cold with a foot pump into
the overflow line (through the pressure release valve in the cap,
which is on). There is definitely pressure in there now (I can feel it
in the rad hoses). I've left it some minutes and it seems to be
holding. How long is necessary is up for debate.
Assuming it holds the pressure tho (for some tens of minutes), does
that tell me anything with the thing cold. How different would it all
be hot (and I am considering that hot with these things is not a huge
As to the aux fan, I don't have one of those. Just the engine driven
one, and the viscous coupling feels quite stiff to me, so I surmise
that is OK.
You're right about the temps tho. Even for Blitey, we've had some
cracking hot weather. Nothing upto USA standards, but almost 100f in
places here. The humidity is pretty high though, which is wilting us
I gotta say though, my Toyota Hilux (4-runner) diesel and my GM
runabout never gave me the slightest cause for concern in the heat.
My classic car buddy at work is convinced its the rad that is blocked.
Maybe the leak stopper I put in has finally bunged it up.
What do you think. A new rad for good measure?. I could maybe get a
re-core for $150 and all new for $200.
The pump is a definite candidate for swapping. There is definitely
some slight vertical play in the bearing. The pump will cost me $150
100 degrees C. is to be expected from a gas engine in traffic on a hot
day - not a problem - normal.
Pressure in the cooling system does nothing about its temperature,
pressure simply raises the coolant's boiling point so the motor can run
hotter w/o boiling.
The radiator can be dirty outside as well as inside so an easy fix is to
clean its coils with a garden hose (first cover the motor and alternator).
Water pumps are a matter of confidence - I found M-B rebuilt pumps well
worth the (small extra) $ vs. some Brand X that failed after 5K miles!
You're a clever guy - to pressurize the system through its overflow tube
- I never would have thought of that.
Just a quick update
Well after two days (I've been busy and claim all the usual 21st
centuary excuses), the system still has pressure, and quite a
reasonable amount (hoses still noticeably hard).
Points to note are that the radiator is showing signs of several leaks
(weeps) accross the front area of the cooling surface. I can see a
number of damp patches, some as big as a quarter, one maybe 3 inches
across. The fact that there is pressure whilst cold means that the
coolant is not evaporating quickly with the heat/air movement so its
very easy to see.
I guess what this is pointing to is I need, at the minimum, a new rad.
Maybe that is where all my pressure went. A new leak opened up, was
quickly sealed by the coolant additive, but meant I ended up with no
pressure. I reckon that the core maybe blocked as well, hence the
severe reduction in cooling power.
Anyway, I'll order a new/exchange rad and get that fitted to start
with, and throw in a new stat as well.
Cheers again Tom.
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