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  #1  
Old 10-15-2003, 01:26 AM
unkl300d's Avatar
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Location: San Francisco, Ca
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Question '79 240D, radiator/ hose question......

Hello, on a 1979 240D with about 133K miles I have observed a curious situation.

I read the archives and gleaned some hints but no answers.

Situation:
The car operates fine in City drives and long freeway drives in outdoor temps of 70F.
The temp gauge reads about 85 Celcius, which I consider normal.
No events of overheating and the system was 'apparently'flushed
about a month ago.
the coolent seems to warm up to operating temp normally versus a sharp jump.
The radiator fins are clean on the outside and the records show that the car has been well maintained.
The odd thing is that the top radiator hose is hard and HOT
when at operating temp whereas the lower hose is pliable and warm.
On my 1979 300D, the top hose does remain pliable when at operating temps (just above 175F) however I have not checked to observe for top/bottom hose temp differences.

So since it is not overheating, I would suspect some to say to leave well enough alone, however I don't really know if this situation marks the beginning of a service problem like the need for a new water pump or T stat (T stat changed about 3 years ago, new belts about 1 year ago). Or perhaps it was not burped properly and there is an air pocket in the system???? K.I.S.S.

So, please offer me your opinions.

Thanks

Denis

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD
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Old 10-15-2003, 02:19 AM
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Dear Denis:

My 300SD's cooling system behaves similarly. However, I believe that's perfectly normal because MB cooling system uses a bypass system. When the cooling temperature is around 80C or more (depending on your thermostat), the thermostat gradually starts blocking the bypass hole, forcing hot coolant from the engine block to flow into the upper radiator hose and move to the radiator to be air-cooled. If you do not run your car long enough (usually 15 miles+ or 20 minutes +), there isn't enough hot coolant to move to the bottom of the radiator and into the lower radiator hose (remember that the hot coolant is continuously cooled by the radiator fins when it's moving down the radiator). Therefore, the lower radiator hose will always be slightly warm while the upper radiator hose is actually hot if you don't run your car long enough.

If you don't believe my "theory", just try to run your car for at least 30 minutes + or 30 miles +, then you will see that the lower radiator hose is just AS HOT AS the upper radiator hose.

Hope this helps.

Best regards,


Eric
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  #3  
Old 10-15-2003, 02:28 AM
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Join Date: Jan 2003
Location: USA
Posts: 699
Dear Denis:

There's another point I want to mention. If you run your car long enough but the lower radiator hose is still only very slightly warm, you definitely need to replace your thermostat. Bad thermostats may not close the bypass hole completely, and so not enough hot coolant is forced to flow to the radiator through the upper radiator hose.

Eric
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  #4  
Old 10-15-2003, 09:01 AM
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Join Date: Sep 2001
Location: central Texas
Posts: 17,281
If you can squeeze your lower hose... REPLACE IT NOW... it will only get softer... or
,,, at some time which is NOT predictable.... it will start to collapse AT SPEED, causing over heating FAST... and the cause will not be obvious.. since this is the suction hose.... it is supposed to have a wire coil in it to keep it from closing at high suction times..
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Old 10-15-2003, 10:02 PM
unkl300d's Avatar
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Join Date: Jul 1999
Location: San Francisco, Ca
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Thumbs up Rad

Thanks Eric and Leathermang,

Today I felt the hoses of my 300D and it was about the same temperature-wise as the 240D, i.e. top hose hotter than lower hose.
This test was done just under operating temp.So Eric you have a good point.

I will later test the hose temp difference on the 240D after a long drive.

However, should the top hose really be so hard? The 240D's top hose is hard and hot to the touch after a long drive (45 minutes).

I really don't think my 300D displays this (hard and hot top hose) , but I will have to re-observe it later when I have the opportunity.

My lower hose on both cars are not mushy or butter soft. They are not rock hard, however.
So thanks for the heads up.

I'll try to burp the system and keep an open mind bout the t-stat,

Thanks.

Anyother, opinions are welcome.

Denis

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD
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