280SL 1968 Hot engine

[Thierry du Laos]

Dear all,
I was suspicious on the engine temperature but got confirmation today, it overheats....
I idle in my garage he rised up to 100 C. And I stopped there !!
The engine is as I got it from the USA with the car.
I have a new radiator, and took out the thermostatic valve!!!.
I suspect a problem with the richness, and eventually air in the cooling system?
Any suggestion and ideas for troubleshooting are welcome!?
Thanks....!!!!!
Thierry

[Tyler S]

Another thing to check is the fan clutch.
Shut the car off when its hot and try to spin the fan. It Should NOT freewheel. It should be very stiff to turn.
You can remove trapped air by removing the upper heater hose on the left side firewall and filling the system until no bubbles are present.
Re-install the thermostat as this can cause issues. There is also a bypass upgrade that can be performed to the hoses on the head.

[Mechudo62]

If you just got the car, I would recommend removing and servicing both the oil and coolant radiators, performing a back flush as described in the Technical Manual and making sure your water pump and thermostat are functioning properly. Get the appropriate BBB for your model and follow the procedures described to correctly service your cooling system. Check to see if a previous owner modified anything and that all parts are there including a fan shroud, and return it to factory specs. Do not alter or remove parts from the system, as this may complicate things further. Fill the system with Mercedes-BENZ coolant and "water wetter". Keep in mind that all engine subsystems in these cars are interconnected and modifying one, will have repercussions on another. If it still overheats after the proper cooling system maintenance, check the timing and the fuel system to make sure they are tuned to factory specs. 

[Thierry du Laos]

Thanks, I will check all these and let you know.
By the way, I will check the thermostatic valve as it is out. What is the temperature for opening? About 80 C?
Gathering info from the previous owner will be difficicult as I got the car from a dealer in New York via Internet, not the owner....
As I took out the engine to refurbish the car ( but did noting on the engine), there is new oil and coolant.

When I re-installed the engine and started, I had an engine too rich. After a few minutes, the spark plugs got really black So I took out the wear plays of the linkages, and adjusted to minimum the struts to reduce fuel. (Didn't touch the pump adjustment) Now, the spark plugs look normal.

When I got the car, not drivable, just the engine running, I didn't notice any overheating at that time. Seemed all normal.
I suspect something different after re-installing...
That's why I suspected air in the cooling circuit, richness...
Thierry

[ja17]

Removal of the thermostat will make the problem worse. The thermostat is double acting. As it opens one passage it closes another. Do not leave it out. Try using one with a lower opening temperature if you like.

[Thierry du Laos]

What is the theoretical opening temperature of the valve?

I think you're correct Joe. Thinking to your post, it got worse than before removing.
I'll put it back.

[ja17]

Thierry, the opening temperature should be stamped on the thermostat in C.

[Benz Dr.]

The coolest thermostat is 79C as far as I know. If you continue to have hot running problems you can remove the thermostat and drill a small 1/8'' hole through it which will allow air to escape but not affect function. I know that in very warm climates some owners just run water in their cooling systems. Don't do that and use at least some anti freeze to protect your system from rusting. Coolant also has a water pump lubricant additive which you need.

[lurtch]

The cause of my over heating problems became obvious when I pulled the head and found those pencil-eraser sized coolant passages between the cylinder bores were almost entirely clogged by corrosion.

Larry in CA

[Thierry du Laos]

Thanks Larry, I hope I won't have to do that.

I just re-installed the thermostatic valve after checked it ok. Double valve starts opening from around 75C..
Ran again, not over heating, but think the fan hot or cool is the same viscosity!!!
And still running too rich!!! 6 same black spark plugs after idling a few minutes, until the engine stops itself too rich.

[Mechudo62]

The fan clutch on my 1970 280 SL engages at around 80-90 C and the temperature in city traffic may get  beyond 100C. However, once the fan revs faster with the clutch engaged, temperature hovers around 100C or slightly lower and will not overheat but I don't dare turn the A/C on... Go over the throtle linkage tour in this site and make sure all rods are perfectly aligned in your car. Also make sure the throtle body round Venturi opens and closes as designed. Do not adjust the fuel injection pump mixture until you make sure this system is properly set and the fuel injectors are clean. I would also recommend watching Kent Bergsman's Pagoda Rescue on YouTube for more detail on dealing with rich fuel mixture. Good luck.

[GGR]

You can do the news paper test. Get the engine to a temperature where the fan clutch should be engaged. Roll a news paper and while the engine is running, try stopping the fan propeller with it. If you can stop it then the clutch is malfunctioning. If so you can replace it, or try refilling it with wax. You may find details on the process on the net.

For your richness issue, you may look into the "linkage tour" thread, as something off there will throw mixture off. Also on engines that did not run in a long time the rack in the injection pump may end up sticking (cremaillere gommee). You can free it by accessing from the front of the pump.

[Thierry du Laos]

Good advices.
I went through Kent Bergsman's Pagoda Rescue on YouTube, but unfortunatly the videos are not in order and th one I'like is missing. I think it is to push the readers to pay for!
However I went through the air intake valve adjustment, it was 1mm far from correct sticking closing.
Then adjusted the pump link to have the engine starting and running nice. And reconnected/adjusted the link to the pedal. So far it runs, sounds better, and no overheating.

I didn't touch the pump at all as the engine was running nice when I got her. So it had to be something else that is wrong.
Now I need to make the news paper test on the fan!

Then for more I will wait to get the seat rails from France at my net trip, and attach my seats in the car, before going for the first test drive out of the garage.
I feel better and optimist this evening after this last adjustment.
It is true that this system is dramaticly sensitive to the wear of the bearings and ball connections.
Thanks a lot guys for the good info.

[gorgoo]

Hi Thierry,
Running rich won't make you engine any hotter, that's running lean which may increase combustion heat up to the point of blowing a piston. No risk it happens at idle though. So excessive richness has to be adressed (is already?)but is not the cause of your overheating.
Visco coupling of the fan maybe if you don't feel any difference between hot and cold. Maybe you could temporarily adapt an electric fan in the front grille and check if heat building is controlled.
Then you should think radiator: has it been cleaned? Could be full of silt if car has been stopped fo years. Not many solutions apart from changing the core. If yours is plugged, nothing will pass in the tubes, acid cleaning won't work.
Finally check the water pump impeller, sometime they break.
Ultimately it may be silt in the engine block, this would spell "big overhaul" of engine.
As mentioned before, thermostat opening temp is stamped on it (see pic), don't run without one.

Bon courage!
Didier

[Thierry du Laos]

Bonnjour Didier,
You are correct, I think the overheat is addressed, it is a hot engine!!!
I made the news paper test, and its ok.
Themperature is back to around 90C, runnning, so correct.
But I still have the problem with the linkage adjustment between the air flap and injection pump!.
That' why I raised a new topic to ask about the angles between the levers on the shaft wich makes the liaison on top of the engine.
I removed it and refurbished. But now I wonder if I didn't make a mistake when I re-assembled it???
The engine was running fine when I got the car. The car couldn't be driven for so many other problems, but the engine was good.
So I think, my problem now is re-assemblying something the wrong way....
(My private e-mail is savidan_thierry@yahoo.fr to ease writting in french and not bother the forum community)
Thierry