500SEC Boiling when at idling (stand-by) app 600rpm for more than 6-8min - Mercedes-Benz Forum
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post #1 of 92 (permalink) Old 06-16-2019, 06:43 AM Thread Starter
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500SEC Boiling when at idling (stand-by) app 600rpm for more than 6-8min

Bros, i know i have pulled this before, but the status is a little changed. And im very confused about what is the problem. Will try to explain:

lately my 500 1983 Euromodel has been working well again. - It was a problem before, been running well and no problem for 2weeks, but now similar problem are back yesterday.


- Yesterday and today at stand still in traffic jam it overheat (motor boiling) motor temp raises to above 120 C

This is only at idling (only if i stand-still in traffic jam with minimum rpm for more than 6min) temp raise from normally 92C to 120C+ within 5-8minutes. (outside temp has been around 26C) at both times this happen.

FAN running. OK.

NOTE: If i give a little trottle and rush the engine to 2000-3000rpm when in this situation (stand still) for 1min, then temp drop back to normal 90C. And the problem dissapear for new minutes.

So it is never a problem if i have a little rpm (over 12-1300rpm) and never when driving. And not a problem when i have a short stop for less than 3-4 minutes.

Rpm at idling (stand-still) is approx 600rpm and oil pressure is approx as always been 1.8 (same as my other 500SEC.)

No other problems experienced: Motor pulling well, no smoke, nothing to report, no use of cooling water.


What can it be?
- Termostat ?
- Electrical or some sensor issue?
- Air in coolant water?
- Poor coolant water quality, time to change?

- Other ?



Support is appriciated a lot, - Where to troubleshoot?
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post #2 of 92 (permalink) Old 06-16-2019, 10:29 AM
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You have two fans , the mechanical engine fan controlled By a fan clutch and the electric auxiliary fan . If you mean the electric auxiliary fan is coming on at high speed then your fan clutch for the mechanical fan is bad

The symptoms you describe sound like a bad fan clutch , assuming your electric fan is coming on
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Last edited by tusabes; 06-16-2019 at 10:33 AM.
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post #3 of 92 (permalink) Old 06-16-2019, 10:57 AM
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+1 @tusabes You need to make sure your electric fan(s) are coming on.
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post #4 of 92 (permalink) Old 06-16-2019, 02:15 PM
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To check the viscous fan clutch, with the engine off, spin the fan by hand. It shouldn't go more than about 1/4 of a revolution. My slightly overly stiff fan stops in a couple inches - noisy thing but helped immensely with Las Vegas (10% of the surface of the sun temps) summer heat.
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post #5 of 92 (permalink) Old 06-16-2019, 04:54 PM
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I too would suspect the fan clutch. Since raising the RPM cools it down, it sounds like the clutch never engages. The "spin" test is not 100% reliable, but if the fan spins free enough to make a full revolution, it is definitely bad. It is possible to pass that test and still not engage, however.

When the coolant temp gets over about 110 the clutch should definitely lock up, and you should notice the roar of the fan. This happens rather suddenly. If you don't, replace it regardless of how the spin test went.

One more thing to check, which came up in a recent post by someone else. Make sure the electric fan is blowing into the engine compartment and not out the grill. The two fans are supposed to compliment each other...
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post #6 of 92 (permalink) Old 06-17-2019, 12:08 AM Thread Starter
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Hello guys. appriciated fast and good replys from all of you,

Please clearify:
1 Electric aux fan. At what temp schould it start (105C ??) or other
2 Electric aux fan. Shall it start at above temp, also when AC or heater is off ?

3. Which of the two fans shoud only be spin 1/4, mechanical or the smaller elec aux fan?
4. Where is fan clutch located, and where is a quick guide on web to replace?

Best
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post #7 of 92 (permalink) Old 06-17-2019, 04:35 AM
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Those old enough to recall will know that it used to be like that for every car. My dad's brand new Buick overheated when we were stopped on the highway by a bad accident ahead. He thought that he did not have to get out, shut it down, and raise the hood like the other drivers in line.

Thank traffic jams for getting manufacturers to increase radiator performance. Yours is just old.

Sorry your new radiator will be so expensive over there. But, best of luck. Don't spend too much money fooling around with the fan. The increased idle tells us that it is likely not a fan problem but a circulation problem.
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post #8 of 92 (permalink) Old 06-17-2019, 05:28 AM
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Quote:
Originally Posted by GT1 View Post
Hello guys. appriciated fast and good replys from all of you,

Please clearify:
1 Electric aux fan. At what temp schould it start (105C ??) or other
From memory, it comes on in response to pressure in the AC system. On a hot day, it will probably be on most of the time the A/C is on and the car is not moving. More than you probably want to know here.
Quote:
2 Electric aux fan. Shall it start at above temp, also when AC or heater is off ?
Yes, it will come on if the coolant temp rises above a set point, around 105C, IIRC.

Quote:
3. Which of the two fans shoud only be spin 1/4, mechanical or the smaller elec aux fan?
The mechanical fan. At normal temperatures the fan is driven at less than engine speed by the viscous fluid in the clutch. When the temperature of the air coming off the radiator reaches the fan's set point, the clutch "locks up" and the fan is driven at engine speed, up to a certain point, above which the fan maintains a relatively constant speed.
Quote:
4. Where is fan clutch located, and where is a quick guide on web to replace?
It is between the fan itself and the drive pulley. #10 in the diagram,

MBL87560SEC and oldmako like this.
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post #9 of 92 (permalink) Old 06-18-2019, 12:20 AM Thread Starter
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Quote:
Originally Posted by John350 View Post
From memory, it comes on in response to pressure in the AC system. On a hot day, it will probably be on most of the time the A/C is on and the car is not moving. More than you probably want to know here.

Yes, it will come on if the coolant temp rises above a set point, around 105C, IIRC.


The mechanical fan. At normal temperatures the fan is driven at less than engine speed by the viscous fluid in the clutch. When the temperature of the air coming off the radiator reaches the fan's set point, the clutch "locks up" and the fan is driven at engine speed, up to a certain point, above which the fan maintains a relatively constant speed.

It is between the fan itself and the drive pulley. #10 in the diagram,

John, Thanks so much for prompt and good reply, will check all when im back home.
Excellent explanation
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post #10 of 92 (permalink) Old 06-23-2019, 02:00 PM Thread Starter
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Back from a buiss travel. Did 1hr work with this car today. So far i find and have this info:

1) The mechanical (biggest fan towarts motor) spin MAXimum 1/4 its very hard and i would say it spins only 15% of a full turn. So i guess Clutch issues might not be the problem after all.

2) Waited 15min in 29C. To wait for temp to raise (stand by , maybe 500-600rpm, no trottle at all. Stand-still waiting.

the smaller fan in front never came on or started. Even when temp was between 110-120C. Then i stopped the test.

3) Tried to turn AC on and OFF during test. AC working OK. No prob.

Small (electric fan NEVER started all the way from cold engine 60C to hot engine 115C or something.

NEED ADVICE QUICK.
1) I think my problem is the electric fan, agree? (see picture "electric fan in front of car" below, this one right ?)
2) If not electric fan what can it be?
3) How to troubleshoot to be sure electric fan is broken (pull wire from battery direct to fan clamp?)
4) If fan, where to by replacement or repair part cheap in Europe or us (e bay) Send link please.
Will attach pictures below.
THANKS FOR ALL SUPPORT Again, highly appriciated ! BEST
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