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  #1  
Old 08-03-2008, 06:07 PM
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Running hot??

Since the guage on a MBis in C,what is the acceptable running temp(summer) for a 83 300SD? Seems the guage is close to 120 C.....
Thanks in advance......BTW...the oil pressure as well mine is @ 3 (top of scale) when driving and stays @ 2 @ idle.......
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  #2  
Old 08-03-2008, 06:12 PM
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The thermostat is rated for 87C so 120C is definately too hot. I'd be suspicious of the t-stat and radiator. The t-stat may be sticking and is the cheap easy to replace part so you should start by replacing it first. Given the age of the car it is very likely that the radiator is partially corroded and clogged internally. With a known good t-stat you can chek the raditor by feeling for cool spots right after a high speed drive with an immediate shut down.

If the car will cool down when running at high speed then you may have a failing fan clutch that isn't moving enough air when in stop and go traffic.
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  #3  
Old 08-03-2008, 06:59 PM
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Quote:
Originally Posted by duxthe1 View Post
The thermostat is rated for 87C so 120C is definately too hot. I'd be suspicious of the t-stat and radiator. The t-stat may be sticking and is the cheap easy to replace part so you should start by replacing it first. Given the age of the car it is very likely that the radiator is partially corroded and clogged internally. With a known good t-stat you can chek the raditor by feeling for cool spots right after a high speed drive with an immediate shut down.

If the car will cool down when running at high speed then you may have a failing fan clutch that isn't moving enough air when in stop and go traffic.
Maybe I shouldn't have said 120C it was firly close though. But since I just purchased it,I'll be checking what you suggested...forgot to mention,that was with the A/C on...if it matters......
Thankyou!!
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  #4  
Old 08-03-2008, 10:50 PM
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That matters a great deal and changes the diagnosis...the question now is do the aux fan/s come on in front of the radiator when a/c is on ..and does the car NOT o-heat with a/c OFF ?????
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  #5  
Old 08-03-2008, 11:09 PM
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Originally Posted by Arthur Dalton View Post


That matters a great deal and changes the diagnosis...the question now is do the aux fan/s come on in front of the radiator when a/c is on ..and does the car NOT o-heat with a/c OFF ?????
Will have to check & see...didn't hear the fans but looking is better than listening!! Thanks
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  #6  
Old 08-03-2008, 11:38 PM
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The aux fans come on when the a/c high side presssure starts to climb up there...so, with no additional airflow to combat that extra thermal heat burden, the radiator gets passively heated from the a/c condenser and the engine o-heats..usually at low rpms or traffic.
Here is the switch that activates that circuit and there is a simple test I use to verify that circuit in the event that you do in fact find that you have no low fans w/ac ..

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FG17RJ3A2FK1BPDOF&yearid=1983@@1983&makeid=MB@@MB@@X&modelid=300%2DSD%2D002@@300SD&catid=R@@Climate+Control&subcatid=R1055@@A%2FC+Temp%2E+Switch&mode=PA&subcatid=R1055@@A/C%20Temp.%20Switch&applicationid=000024786&source=www.peachparts.com&clientid=catalog.mercedesshop

You will notice that it is referred to as a temp sw , but in reality it is pressure sensor type sw and monitors the high side refrig pressure .
So, the test:
If you have no low fan w/ac On and a good hot ambient temp condition, you peel back the insulator sleeves on the pigtail end of that sw [ it is located at the reciever/drier ]. and jumper there with anything ...a screwdriver blade is fine... low fan/s should come ON ..if yes , the circuit is verified ...if NO, you have a fuse or relay problem ..or even a bad fan motor..
Now for the tricky part...
There is a time when the fan circuit passes the jumper test , but it still does not come on with the a/c on...the reason for this is usually b/c the a/c system is slightly low on refrigerant..not enought to trigger the fan,but still enough to give you a/c [ altough not max] ..so you wind up with no fan , a moderate a/c output, and an O-heated car....tricky diagnosis that fools many a seasoned guy. Just a few ounches light of refrigerant will bring on this condition, so something to watch for if your fans are not comng ON , but they do pass the jumper test..
Of course, you could also have a bad sw...but the refrig level is always the first suspect b/c they seep over time ... no matter what.

Check the fans.........
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  #7  
Old 08-04-2008, 12:11 AM
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Quote:
Originally Posted by Arthur Dalton View Post
The aux fans come on when the a/c high side presssure starts to climb up there...so, with no additional airflow to combat that extra thermal heat burden, the radiator gets passively heated from the a/c condenser and the engine o-heats..usually at low rpms or traffic.
Here is the switch that activates that circuit and there is a simple test I use to verify that circuit in the event that you do in fact find that you have no low fans w/ac ..

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FG17RJ3A2FK1BPDOF&yearid=1983@@1983&makeid=MB@@MB@@X&modelid=300%2DSD%2D002@@300SD&catid=R@@Climate+Control&subcatid=R1055@@A%2FC+Temp%2E+Switch&mode=PA&subcatid=R1055@@A/C%20Temp.%20Switch&applicationid=000024786&source=www.peachparts.com&clientid=catalog.mercedesshop

You will notice that it is referred to as a temp sw , but in reality it is pressure sensor type sw and monitors the high side refrig pressure .
So, the test:
If you have no low fan w/ac On and a good hot ambient temp condition, you peel back the insulator sleeves on the pigtail end of that sw [ it is located at the reciever/drier ]. and jumper there with anything ...a screwdriver blade is fine... low fan/s should come ON ..if yes , the circuit is verified ...if NO, you have a fuse or relay problem ..or even a bad fan motor..
Now for the tricky part...
There is a time when the fan circuit passes the jumper test , but it still does not come on with the a/c on...the reason for this is usually b/c the a/c system is slightly low on refrigerant..not enought to trigger the fan,but still enough to give you a/c [ altough not max] ..so you wind up with no fan , a moderate a/c output, and an O-heated car....tricky diagnosis that fools many a seasoned guy. Just a few ounches light of refrigerant will bring on this condition, so something to watch for if your fans are not comng ON , but they do pass the jumper test..
Of course, you could also have a bad sw...but the refrig level is always the first suspect b/c they seep over time ... no matter what.

Check the fans.........
Good to know....I had a feeling something with the blower/a/c temp switch is bad...This guy rewied or by passed the blower swich (low/high) with two toggle switches...bet he screwed something up!!
Looks like I got some work to do.....lol
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  #8  
Old 08-04-2008, 12:23 AM
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If you have no fans w/ac on, Your first test should be that jumper test.

Most Fail that test and wind up just being the aux fan fuse..mostly b/c Benz had a habit of under-rated fuses on that circuit and the fan motor gets old and draws a little more current than when new..
If you do have such a condition [ w/blown fuse ] , also spin the fan motor by hand to make sure it is nice a free..they get full of crap and that drag blows the fuse.
You will find it..........
And if the fan/s do work with a/c on as they are supposed to, and the engine still o-heats with no a/c on, then the diagnosis goes right back to Duxs original..
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  #9  
Old 08-04-2008, 12:36 AM
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Sounds like you need to go through the cooling system.

Check radiator, replace probably if it looks original.
Thermostat
Correct coolant
Fan clutch if needed
Hoses
Clean AC condenser
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  #10  
Old 08-04-2008, 09:58 AM
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Quote:
Originally Posted by Hit Man X View Post
Sounds like you need to go through the cooling system.

Check radiator, replace probably if it looks original.
Thermostat
Correct coolant
Fan clutch if needed
Hoses
Clean AC condenser
Besides checking what the previous owner did (rigging toggle switches for the blower)I have alot of checking to do...lol

Thank you for the tips!!
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  #11  
Old 08-12-2008, 03:43 AM
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I have a CLK and have a no Aux Fan condition. I swapped out all 5 relays and checked all of the fuses but still the same problem. I have a feeling after reading all of this that it may need an A/C recharge.

If that doesn't work, I'll try the jumper test and then check the resistor. Anyone have an pic of what that night look like?

I love the "turn on the fans whenever I want" idea with a manual switch - A little scarred to try this as I see 2-3 connectors coming out of what I think is the receiver drier. Which one do I attached the two leads from the manual switch to?
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  #12  
Old 08-12-2008, 06:00 AM
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Also change the temp sender, the VDO is notorious for going out of whack and make sure the ground connection is good on the car.
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