89 W126 300SE cooling problems

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.
Read on..
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 anywhere. Also I notice I have no pressure in the coolant pipes. So I realise that I should change the rad, thermostat, temp senser (and also the water pump, which I beleive is making a slight mechanical noise). But Where is the pressure?. Have I a cylinder head problem?
Any suggestions as to a difinitive check to diagnose my problem.
Cheers... Rob.
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I don't seem to be losing coolant either

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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 radiator.
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 radiator.
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).
/Jens
Rob. Smith wrote:

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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!
Tom
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Hello Tom 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 heat (~100C).
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 all. 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 also.
Cheers... Rob.

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Hi Rob,
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.
Happy Motoring.
Tom
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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.
... Rob.

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