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Discussion Starter #1
Hi guys. Recently i noticed my temp gauge needle climbed a bit over the first unmarked white line, i think that is 100 degrees, while in stop and go traffic and with Ac on.
It used to sit a tad over 80 no matter the conditions.
So i checked the 2 fans in front of the rad and they dont spin.
I unplugged the blue sensor with 2 pins that plugs next to the head and both fans started at high speed.
So i guess they are good.
What else should i check next?
I checked also the fuse D in the fuse box, and it seems to be good. But then again, if it were for that fuse to be fried, the fans wouldnt have started when i unplugged the blue sensor, no?
Thank you
 

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The temp sensor itself in the block might bad. How many miles on car? I would replace it anyway.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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For the temp sensor measure it's resistance against the spec's. If it is higher than the spec's by >10% that could be an issue.

But the number one culprit in an engine running hot at idle (or at highway speeds) is the thermostat (assuming it is not >100F or >40c ambient)
That is because the coolant temp is regulated by that component alone. It has to open all the way at the specified temperature (normally 87c)

They get lazy over time and do not open all the way restricting flow. My Behr one only lasted 3 years. Just replaced it. Back to normal.
 

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Discussion Starter #4
The problem is that the auxiliary fans dont turn on anymore.
From what i’ve found on internet, these cars have a 2 stage fans. The low speed should engage once the Ac compressor is on, and the second high speed stage should cut in when the temperature is above 100 or so.
Also the low speed is controlled by Ac pressure and the second only by temperature.
The temperature is a tad over 80 when normal driving, but once i am on idle the temperature rises as the aux fans dont work anymore.
 

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1993 300E 2.8L, 2010 ML350
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They don't work at all anymore? I am having the same issue - I suspect a relay, but not sure how to check
 

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Discussion Starter #6
They don't work at all anymore? I am having the same issue - I suspect a relay, but not sure how to check
They dont work anymore. But they are good as when i unplug the blue 2 pin sensor next to the head, they come in high speed.
So i dont know what and how to check next.
 

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1993 300E 2.8L, 2010 ML350
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So they come on when you pull the plug on the temp sensor, but don't come on when it gets hot or when the A/C is on?
 

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1993 300E 2.8L, 2010 ML350
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Have you tested the connector to the fans when the A/C is on with a voltimeter to check for current?
 

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Discussion Starter #10
It seems that the problem was the D fuse. I checked again yesterday the fuses and the fans work again. They start on low speed when turning the AC on. I hadnt had the opportunity to test the high speed but my guess is they will cut in when needed. Gonna check the temp gauge once i am in heavy traffic.
 

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1993 300E 2.8L, 2010 ML350
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Did the D fuse look bad? Mine looks good but I have yet to replace it and wondering if that may be an issue.
 

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Discussion Starter #12
It looked ok, not melted. But i had good instinct And gave it a shot and replaced it. And problem solved. They sometimes get old i guess.
 

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1993 300E 2.8L, 2010 ML350
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Yeah, I tried that for my issue. No bones. Good to know it worked for ya. When in doubt, check and replace fuses.
 

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Current, 90 300CE, 92 400E (Sold 95 E320,70 250C, 91 190 2.6, 91 420 SEL, 95 300D, 87 TD)
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Fine crack in the fuse?

If you haven't already...you should replace ALL fuses with ceramic/ copper fuses. The plastic/ lead ones create electrolysis between the tabs in the fuses.

The ones that look like lead / chrome should all be replaced.

That's one way to eliminate some electronic glitches.
 

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2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
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The Tin/Lead alloy in the old style fuses develops a very thing oxide layer over time which acts as an insulator thus preventing current flow. Visually, the fuse will look fine. That is why upgrading to copper fuses is so important in these cars.
 
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