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Discussion Starter #1
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?
Best
 

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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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+1 @tusabes You need to make sure your electric fan(s) are coming on.
 

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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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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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Discussion Starter #6
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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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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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.
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.

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.
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,

 

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Discussion Starter #9
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
Best
 

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Discussion Starter #10
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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I had a similar situation on my 500sel, turned out to be the thermostat. The wrong type of t-stat was install, and it acted like yours. Might not be a bad idea to change it, it's cheap enough, and then you can cross that off your list of possible issues.
 

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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
Yes sounds like your electric fan is the problem
Buy an universal adjustable fan thermostat , you can find them at local parts store or eBay
 

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Just wire the electric fan direct from the battery to run all the time and see if it still overheats. When it doesn't, see post 7 above.
 

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Discussion Starter #15
See pics as well below: Thaks

Ahy other sollutions:

1) fan broken / how to check ?
2) Termostat broken as mention ?
3) Any sensor that can be broken ?
4) All fuses are ok, but what about rele`s?

5) Other ?

Thanks a lot
 

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The electric fan is capable of moving a LOT of air. If I recall correctly from my reading, it comes on at a dedicated target temp (100C sticks in my mind) and/or when the AC is on. Whether or not that's 100 percent accurate, it's absolutely got to work in order to keep the engine cool. And that assumes everything else in the cooling circuit is operating properly.

As mentioned, hook jump it directly to the battery and test. If it runs you likely have a circuit / switching issue.
 

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You have two separate wires on the thermostat housing, both plugged onto two different temp sensors. The smaller one is the temp gauge sender, the larger one is the 110+*C sender.
Pull the wire off the large (110*C) sender and short it to ground. The ignition must be on, or the engine running. The electric fan should come on at full speed.
Btw, your fan should be on low speed with the AC on, once the pressure switch on the drier has closed due to the increased pressure in the system.

Either way, by doing the test above, you can rule out wether the fan is bad.

If the fan doesn’t come on, I’d check the fuse first, even if it looks good. There’s a LOT of current going thru the fan fuse, and oxidation is a common problem on these old cars.
 

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Why not just bypass the ac pressure switch at the dryer to test the auxiliary fan motor and at the same time you’ll know if the switch is faulty.
Because what I suggested is easier than having to wrestle with the drier pressure switch. Most times thing are dirty or the connectors are stuck together, and it’s a bitch to separate them.
The plug slides off the tstat sender right away, and all you need is a metal object that fits inside the plug. Presto, you can test the aux fan.
 
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