Overheating and Remedy

[John Betsch - "SADIE"]

I just found the attached dated October 1970. It is an eight page document addressing "overheating." 

So not to burden the site with 8 pages, is it something relevant to share?  I scanned just the first page. (the white on each side is simply an attempt to "help" the older xeroxing)

JB

[WRe]

Hi,
very interessting, thanks for sharing. Maybe you can put the whole document in the Technical Manual.
...WRe

[dirkbalter]

Yes, I would be very interested in that too.
Thank you

[mdsalemi]

Yes, please scan and post to tech manual.

Did anyone actually read it and notice that it says, "despite the presence of the supplementary electric fan"...

So, did we miss the prior "Advanced Service/Product Information (internal)" about this auxiliary fan?

I'm particularly interested in this first bulletin, as somebody sent me this bypass kit. I don't have overheating but having the instructions on how install would be helpful!

[John Betsch - "SADIE"]

I will try to clean up the xerox, scan and then if someone tells how or who to send to for inclusion in the TM, I can do that 

Of course, I have no idea if the bulletin suggestion is a good one or not.  Wouldn't want to have something in the TM that isn't viable.  As they say, once in print it's gospel

JB

[mrfatboy]

Just attach the the finished PDF here in this thread and I can place in TM.

[John Betsch - "SADIE"]

attached as requested

jb

[dirkbalter]

Thank you. Appreciated.

[GM]

Thanks for sharing!

[mrfatboy]

The document has been added to the TM under the cooling section. 

[doitwright]

Did anyone actually read it and notice that it says, "despite the presence of the supplementary electric fan"...

So, did we miss the prior "Advanced Service/Product Information (internal)" about this auxiliary fan?

Late W108"s with AC had electric radiator fans.

[dirkbalter]

Late W108"s with AC had electric radiator fans.

That is correct but it doesn't feel that it it very efficient. I can manually switch it on even if the AC is not running and I do not see the needle drop anywhere significantly.

[doitwright]

That is correct but it doesn't feel that it it very efficient. I can manually switch it on even if the AC is not running and I do not see the needle drop anywhere significantly.

The heater core bypass has been discussed on these forums. Buds sells a kit modeled off the factory setup. One member did extensive testing including radiator recore, electric fan, water wetter, heater core bypass. If I recall, in his case, the most effective method of bringing down engine temp was the addition of an electric water pump.

The heater core bypass should be effective since it allows coolant normally supplied from the cylinder head to the heater core to circulate back to the water pump even when the cabin heat is not on. For cabin comfort purposes, when driving during warm weather seasons, the heater core valve is closed. This does not allow for continuous coolant circulation from the cylinder head. Add additional summer season factors such as higher ambient temperature and perhaps running a compressor from an AC system, the extra drag of the compressor and radiant heat off the AC condenser will increase engine operating temperatures.

[mdsalemi]

As I recall, Dan Caron (Dr. Benz) has always indicated that the ENGINE OIL carries a lot of the cooling load. I don't doubt him for one second.
Some, but not all of our cars have oil coolers, a mini-radiator on the side of the regular radiator.

[John Betsch - "SADIE"]

my apologies for stirring up such a discussion, promise not to do it again

jb

[ja17]

JB (Sadie), when you get such a discussion, it means your post was very engaging and a big success! Thank you, I now have some new factory "product information" to add to my library.

[WRe]

Hi,
this document is very valuable because it shows that our cars have a construction-conditioned problem with overheating not only with an aircondition.
In my opinion the visco clutch/fan works not effective enough in critical situations because of low revs.
I never had problems with overheating except when it was really hot outside together with a traffic jam on the autobahn and stop-and-go same in the city or climbing on high Alpin passes.

I tried to optimize the original cooling system:
- flushing the cooling system with citric acid: there was a lot of deposit coming out of the system
- new visco clutch: more than one new clutch came already faulty
- new water pump and thermostat
- a fan shroud to optimize air flow
- a by-pass cooling water line
But nothing really helped. Maybe I should have rebuild the radiator too.

After that I've installed the electric fan instead the visco clutch I never had a critical situation with overheating. It's not a solution of striking simplicity but it helps.

I believe too that engine oil carries cooling load but I never had more than 80°C of oil temperature (temperature sensor in the oil pan instead of the drain plug).  Water gets hot very fast and corresponds with engine revs and driving situations. But "high" oil temperatures last some time and miles. In normal running situations my oil became only 60-70°C (with oil cooler). In my understanding this doesn't match together.
...WRe

[dirkbalter]

My experience is similar. I usually drive my 108 a couple of times to the office during the week. As long as I am moving, the temperature will stay at 175 F. On hot days 90 F+ and hitting stop and go traffic, I see the needle going up tp 190+. Turning the AC of and leaving the fan on, doesn't really seem to help a lot. If I put the car in neutral and rev the engine a little bit the needle will drop right away. I could see an electric water pump as suggested above helping.     

[ja17]

Upgrading the radiator seems to be the most significant improvement on cars that have overheating issues.

[mauro12]

I think the 250sl model is the lowest risk car for overheating , compared to the 230 and 280. This is due to a bigger coolant capacity .
I’ve always wondered why the 250 was constructed with bigger radiator capacity compared to the 230 and 280.
By the way is very common issue the overheating for the 280sl.
What I do in my car is to use only mb blue coolant , 79degrees thermostat and new water pump and hoses .

[dirkbalter]

Upgrading the radiator seems to be the most significant improvement on cars that have overheating issues.

Joe, what exactly do you mean by upgrading the radiator?

[MikeSimon]

As I recall, Dan Caron (Dr. Benz) has always indicated that the ENGINE OIL carries a lot of the cooling load. I don't doubt him for one second.
Some, but not all of our cars have oil coolers, a mini-radiator on the side of the regular radiator.

I am a little confused here. My car has a transmission oil cooler there for the automatic transmission. Are you saying there is an engine oil cooler on manual tranny cars?

[mrfatboy]

I believe he is talking about the oil cooler on the left side of the radiator on 280sl’s. Both manual and auto.

See pic with blue arrow.

[ja17]

A lot of owners are upgrading the radiators by having them re-cored with a heavy "heavy duty" core which has an additional layer of cooling tubes. These have three layers of cooling tubes and fins instead of two, I believe?

[dirkbalter]

A lot of owners are upgrading the radiators by having them re-cored with a heavy "heavy duty" core which has an additional layer of cooling tubes. These have three layers of cooling tubes and fins instead of two, I believe?

Got it. Thank you