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  #1  
Old 09-01-2002, 12:06 AM
cKoeller
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Hello,

I have a 1972 280se 4.5 MB.

How hot should the gauge max show? What is the ideal Highway Temperatur? At what temerature should I get worried?

Also when should the aux fan kick in? at the temp over 175? or only when the A/C is on?

cK

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  #2  
Old 09-01-2002, 01:27 AM
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The Aux Fan should kick in if the temp goes over 212.
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  #3  
Old 09-01-2002, 01:32 AM
cKoeller
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Are you sure??

220f its near red yes? What with A/C?

cK
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  #4  
Old 09-01-2002, 01:35 AM
cKoeller
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What is the temp mark after 175?

cK
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  #5  
Old 09-01-2002, 02:50 AM
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The unnumbered mark between 175* and 250* is approximately 200*F. The Aux fan should kick in about 212*, the temp sensor for the fan is a 212 switch. Being low on freon may effect the cut in of the aux fan.

Mine shows a steady 195* or so during highway runs, a touch warmer in traffic.
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  #6  
Old 09-01-2002, 09:43 PM
zorak
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i was actually about to ask the same question, i am glad someone else posted about it. my car usually runs with the needle between the 175 and the 200 mark and i was wondering if this was normal... would i be safe to assume this a healthy running temperature?
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  #7  
Old 09-01-2002, 10:54 PM
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Those 4.5s should run right about the 175* mark. You can get a 68 ohm resistor, and use it to check the gauge accuracy. Connect to the lead to the dash unit and ground. Turn on the key and you should read 175* on the dash. Also at operating temp the sender should read 68 ohms.

Peter
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  #8  
Old 09-02-2002, 09:56 PM
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And for those not on the mercedes veteran's list, there was a similar thread there. If you're running hot, check two things first...

1. If you replaced the thermostat recently, did you happen to notice if it had a little BB for a check valve ? And if it did, was the thermostat oriented so that the BB was at the highest point it could be ?

2. Your radiator is probably inefficient. If it hasn't been removed and cleaned in your recent memory, it is probably due.

-CTH
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  #9  
Old 09-02-2002, 10:11 PM
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I just got my 280 SE 4.5 running today. Ran at 180 or so (just above the 175 mark) until I drove it a while and then let it sit at idle while I was airing up the tires at a buddy's.

The aux fan came on, and the idle speed ran up, as it was supposed to, but the needle was above the "between" mark, nowhere near the red, but too high for me, so I drove it back home. Temp dropped to about 175 on the way, slowly.

I have no idea what condition the rad is in, although it looks pretty good. I didn't have coolant in it, just water, and the water pump leaks enough to throw water off the fan, so I expect that I have water boiling in the head at idle. It won't pressurize above 7 lbs due to the leaking water pump, anyway.

I expect a good flush with MB citric acid will help, along with the water pump replacement. I had the same sort of thing going with the 220D, and when I got the new water pump in, the temp stopped going so high, probably because the coolant wouldn't boil.

Peter
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  #10  
Old 09-03-2002, 08:33 PM
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Some 4.5's just run warm!

I got my 280se 4.5 about 10 years ago, with 107,xxx original miles. Car in mint shape, but my MBZ Shop noted it running just a tad warm..........so we put in a new rad, replaced ALL the hoses, new T Stat, fan clutch...etc. To this date, and 10,000 mi later, she still runs warmer than others. We have tested the guage and even checked it with a direct reading guage (the sender is located at the rear of the block at the hottest possible place). Everything shows an accurate reading, 212 switch works fine.

We even measured the WP pully size.......I would not let them pull the pump off, every thing is so clean inside!

My MBZ shop owner and I go back almost 30 years as friends, and we have seen many 4.5's run like this......can't figure it out.

They never overheat, or boil over......just run warmer.....most noticed when the ambient air temp is 80F and up.

I don't like to see the guage up there, but the car doesn't seem to mind.
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  #11  
Old 09-03-2002, 08:41 PM
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Note!

never used a drop of coolant, and I have changed it at leat 3 times in the last 10 years.........thinking about trying Red Line Water Wetter.....I think that's what its called.

Any input on this product would be great!

Hey I should just shut up and go drive her, poor thing only get's out every few months.
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  #12  
Old 09-03-2002, 09:00 PM
cKoeller
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Autsch Hot. Vorsicht!

Thanks for all the help.


cK

I would not use Red Line Water Wetter because you have to increase the radiator pressure by 50% to 23 psi. Thats no good.

To much pressure to much bumb....

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