My SEC just dangerously overheated. Need help. - Page 7 - Mercedes-Benz Forum
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post #61 of 210 (permalink) Old 08-17-2018, 10:06 PM
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i know this guy has his issues with the forum..whatever

but his how to threads area really good.....for more info

https://www.500eboard.com/forums/showthread.php?t=12056
I agree 100%. A ton of good info on both forums of which I am a member of. If we can tolerate the odd disagreement we will reap the rewards.
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post #62 of 210 (permalink) Old 08-18-2018, 12:56 AM
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I really cannot tell if the aux fans goes on or not. It certainly doesn't go on before 110. But 110 is insanely hot. I cannot understand why it is designed to go on at a temp that is hot enough to cause skin to be burned when opening the hood. I am really confused by this.
Thats why , for all the people who have never had the the fan come on , you need to follow the directions posted earlier on how to make it run full time , before you ask for a lower temp turn on
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post #63 of 210 (permalink) Old 08-18-2018, 05:31 AM
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Steve My guess is clogged up radiator and it is only working at half efficiency.
Get it tested or simply replace it with a Nissens for peace of mind and will be good for another +10yrs. Flush system first and then add Zerex G-05 mixed 50-50 with water and also replace the thermostat at the same time and clean the temp sensor connections and replace those alloy fuses - they create all sorts of problems.


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post #64 of 210 (permalink) Old 08-18-2018, 06:05 PM
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I disagree. He has problems in low to no speed situations. This points to airflow. A clogged radiator gets worse on the highway.

1783: I think the fan comes (should come) on at low speed much earlier than 110. There's another thread somewhere that covers all the temperature set points. Should it get to 110 it goes full speed as a last ditch measure. That should never happen except maybe in Death Valley in August.
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post #65 of 210 (permalink) Old 08-18-2018, 06:29 PM
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We are now arguing about the details of details.

A clogged radiator cools better in a moving vehicle. Does the airflow overcome the increased fuel consumption (the source of all heat)? Who cares. Replace the radiator as the next step . It is a small cost and almost alwayus an improvement unless it was recently replaced. Like I said on about post #7.
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post #66 of 210 (permalink) Old 08-18-2018, 07:11 PM
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I've been doing a bit of reading about the aux fan lately because I suspect a fault with mine. Here's what I have been able to put together.

The aux fan has two functions:

1. It engages at low speed when the car is not moving and AC is engaged to keep air blowing across the condenser while the car is stationary. It works off a pressure switch on the A/C receiver drier in combination with the climate control system. If your A/C blows warm at idle but cools properly when the car is moving, it could be a fault with the switch itself, it could be that the system is low on freon, and therefore has insufficient pressure to activate the switch, or it could be a blown fuse or a blown aux fan relay (a cube-shaped relay located at the back of the fuse box).

2. It engages at high speed if the operating temp of the motor hits 103-105 degrees (or thereabouts). This is to aid the main fan in cooling the motor back down to normal temps in stop and go traffic in hot conditions. It works off a temperature switch on the thermostat.

(I have observed my aux fan come on high at 105, but suspect it is currently not coming on at low. My A/C is lousy when the car is idling and I haven't been able to observe it coming on at low at all).
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post #67 of 210 (permalink) Old 08-18-2018, 07:14 PM
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IMHO. replacing the radiator would be a waste of money at this point. In 50 years of experience, overheating in traffic has 90% of the time been airflow and overheating on the highway has 90% of the time been been cooling capacity. The kicker is there has been 0% crossover.

Get the fans working correctly first. If that doesn't fix it, I'll be surprised. Or, change the radiator. If that fixes it, I'll be surprised...

(Hint: we already have good reason to suspect the fans don't work right. He hit 110 and didn't notice the fan clutch locking up.)

TMSAISTI

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post #68 of 210 (permalink) Old 08-18-2018, 07:55 PM
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But when he tested his fan clutch with hand and newspaper didn't it pass test... Granted aux isn't going on but he shouldn't get up to 110 of the fan clutch is working....
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post #69 of 210 (permalink) Old 08-19-2018, 05:01 AM
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IMHO. replacing the radiator would be a waste of money at this point. In 50 years of experience, . . . blah blah blah . . .
Then your experience would be wrong. Replacing a 30 year old radiator when air pockets and coolant flow are still in the mix is never a mistake. If you pass by the obvious solutions for the more unlikely based on your old anecdotes you only have yourself to blame.
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post #70 of 210 (permalink) Old 08-19-2018, 05:48 AM Thread Starter
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Originally Posted by newtome190e View Post
The aux fan...

1. It engages at low speed when the car is not moving and AC is engaged to keep air blowing across the condenser while the car is stationary. It works off a pressure switch on the A/C receiver drier in combination with the climate control system. If your A/C blows warm at idle but cools properly when the car is moving, it could be a fault with the switch itself, it could be that the system is low on freon, and therefore has insufficient pressure to activate the switch, or it could be a blown fuse or a blown aux fan relay (a cube-shaped relay located at the back of the fuse box).
It does seem my aux fan is not turning on and perhaps this is the problem. Even at higher temps I did not see it spinning.

I will have to locate that aux fan relay and check it out. I will also check all the fuses. Most are the old aluminum type that are known to corrode. I have a set of better ones on order.

No doubt I should purchase an aux fan relay, even if mine is fine. It's good to have spares. The issue will be, where to buy and which one?

I would love to narrow this down before Thursday, which is when I am bringing the car into the only mechanic here who does German cars. Paying for investigations gets expensive.
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