500E 1991 Fan Viscose Coupling renewal

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paddy@polyposta

Active Member
Joined
Sep 15, 2007
Messages
170
Location
Lincoln UK
Car
500E & RS4 B7
Hi, anyone ever changed the viscose coupling on a 500E/E500?

Some advice would be appreciated, have removed radiator, fan, shroud, pipes to radiators etc. Now with an 8mm alan key placed into centre of bolt which I can only presumme holds the thing on, cannot get it off. Does the bolt turn clockwise/anticlockwise......

PLease help!!!!!!!!!

:crazy: :crazy:
 
I think its a standard RH thread bolt -so anti clockwise to slacken it. You need to jam the water pump pulley somehow to apply enough torque to loosen it. Make sure you get the allen key right to the bottom of the socket head -you may need to clean it out a bit first.
 
Lefty loosey, Righty tighty.

Why do you need to change it?
 
Lefty loosey, Righty tighty.

Why do you need to change it?

Fan not speeding up, working when engine gets hot! System was getting up to 120 deg and loosing coolant/water from somewhere, dod carrot test etc to discover fan only spinning slowly when engine cold or hot! Was advised to change it!?

Paddy
 
DEFINITELY don't do the viscous fan modification unless you want your car to be as noisy as a lorry.

This is the modification you want to do.

http://pages.prodigy.net/jforgione/MB_CTS.html

In traffic and with the air con on I see temperatures of just under 100°C and it's nice and stable. Make sure both auxillary fans are running but i've only had the second stage fan kic in when testing, it never gets hot enough in the UK really if your cooling system is working as it should.

When driving along normally they sit (After the engine gets completely warm) between 80 and 90°C on a run.

I'd do a coolant change if you have no record of it being done in the last 2 years, Mercedes stuff is also surprisingly cheap.

Dave!
 
DEFINITELY don't do the viscous fan modification unless you want your car to be as noisy as a lorry.

This is the modification you want to do.

http://pages.prodigy.net/jforgione/MB_CTS.html

In traffic and with the air con on I see temperatures of just under 100°C and it's nice and stable. Make sure both auxillary fans are running but i've only had the second stage fan kic in when testing, it never gets hot enough in the UK really if your cooling system is working as it should.

When driving along normally they sit (After the engine gets completely warm) between 80 and 90°C on a run.

I'd do a coolant change if you have no record of it being done in the last 2 years, Mercedes stuff is also surprisingly cheap.

Dave!

Paddy:

? Right, dont do it? Been advised by Ian Walker 124works to do so. Hes not mentioned anything about the other fans. In front of the two radiators at the front of the car their are two more smaller fans sat together. I let the car get warm one day when I was doing the carrot test on the large fan on the viscose coupling and these fans were not turning or doing anything so I gave one of them a tap with my finger and it suddenly started up as did the other one when I tapped that? I asked Ian walker about these and he said they are just for the air con and nowt to do with the problem!

So should the viscose coup not be replaced even when its not working then?

The link above looks good as an upgrade but I do not have time at the moment as trying to get the car sorted for MOnday....eek!

I am quite sure the viscose fan/coup has never worked as the car has always run hot, always between at least 100 and getting to 120 in traffic!!

But I was advised that that is the temp these engines run at!

Couldnt quite believe that as its so hot under that bonnet you cant even stand near it.

Over the last few months I firstly had to replace a small water pipe at the back of the engine which was pissing a out water (Done by Ian W 124works) http://www.mbclub.co.uk/forums/showthread.php?t=45434&page=4

Shortly after that the coolant light kept coming on, discovered the expansion tank metal cap was rattling away when engine hot and leaking out coolant. System under an awful lot of pressure. So put new cap on. Since doing that, engine runs even hotter and now on last long run 4 weeks ago or so. Drove to Norwich airport from Lincoln to go on holiday. Temp gauge topped 120+ several times in traffic. Came back off holiday 2 weeks later, collected car and coolant light came on. Exp tank comp empty so pulled in nearest garage and toped up with a lot of coolant and water. Drove off, 3 miles down the road came on again, topped up again and then light never came on again, but temp gauge still topping 120 in slow/still traffic...not good

So was then that I spoke to people got advice and was suggested I change the viscose coup. The new part I have looks nothing like whats on it either..........

Paddy
 
Overheating as you are describing is usually because of inadequate cooling. Stating the obvious really BUT inadequate cooling can arise for a variety of reasons. Failure of the viscous coupling to the engine driven fan is one. Problems with the air conditioning 2 auxilliary fans or their associated circuitry is another. A choked radiator or dodgy thermostat are others. The various tweaks detailed on Jim Forgione's site are responses to overheating problems experienced on these engines in very warm conditions - slow moving in traffic or abnormally high ambient temperatures DESPITE their systems being fully operational. As has been said under normal UK conditions these problems should not arise. However the problems experienced by some drivers in the USA indicate that cooling capacity on these big V8s is "marginal " such that if only one part of the cooling system isn't working to full efficiency then you may experience problems. Provided you have the right replacement viscous coupling it will certainly do no harm to replace it. After that its just checking out all the other cooling components one at at time to get them all working to spec. I may have confused you by suggesting possible modifications. The time to consider this is only once you are completely satisfied everything else is working to spec.
 
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Overheating as you are describing is usually because of inadequate cooling. Stating the obvious really BUT inadequate cooling can arise for a variety of reasons. Failure of the viscous coupling to the engine driven fan is one. Problems with the air conditioning 2 auxilliary fans or their associated circuitry is another. A choked radiator or dodgy thermostat are others. The various tweaks detailed on Jim Forgione's site are responses to overheating problems experienced on these engines in very warm conditions - slow moving in traffic or abnormally high ambient temperatures DESPITE their systems being fully operational. As has been said under normal UK conditions these problems should not arise. However the problems experienced by some drivers in the USA indicate that cooling capacity on these big V8s is "marginal " such that if only one part of the cooling system isn't working to full efficiency then you may experience problems. Provided you have the right replacement viscous coupling it will certainly do no harm to replace it. After that its just checking out all the other cooling components one at at time to get them all working to spec. I may have confused you by suggesting possible modifications. The time to consider this is only once you are completely satisfied everything else is working to spec.

OK Thanks.

The problem is getting the old viscose coupling off, its a b**tch!!

Will try again today.

Does anyone know where the circuitary enters the 2 aux fans, as I said before I tapped them and they came on so maybe a loose wire. Are these activated by the wiring from the coolant sensor on the side of the exp tank?

Paddy
 
Definitely fit a working viscous fan, I never mentioned not fixing it.

I'm saying don't have it so your viscous fan is running more than needed, it just uses fuel and isn't needed.

The 2 electric fans on front of your rad will kick in to keep the temp down, if it gets hotter then the viscous fan will cut in aswell. They are definitely not just for air conditioning, they are mainly for engine cooling.

As standard they work like this (As shown in the link I posted)

Air con on

1st stage runs with your air con on all the time when not moving fast enough, it turns on or off depedant on air con pressure and temp.

Air con off

1st stage cuts in at 100°C - 1 single fan running at slow speed

2nd stage cuts in at 107°C - 2 fans both running at slow speed

3rd stage cuts in at 115°C - 2 fans on flat out

It basically fools your fan (Not your engine) into thinking it's hotter than it is. So when in traffic cuts in the quieter electric fan rather than the viscous one. When mine gets really hot then when the viscous fan is engaged it does make quite a noise when revving it slightly, also the amount of air around the car is huge, they do create a lot of heat, so windows up when this is going on haha.

My resistor mod was done 2.5 years ago and has worked perfectly since then, stable temps in heavy traffic in the heat of italy and cold of england.

I used to do all my own work on the car but now don't have the time so it goes to a local specialist on german cars.

Dave!
 
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cooling capacity on these big V8s is "marginal " such that if only one part of the cooling system isn't working to full efficiency then you may experience problems

Definitely true, there is less space in a 500E engine bay than an SL bay aswell.

For example when working on the resistor mod at one point I had both fans off, it was only idling for a minute or so and the temperature had quickly crept up to 105 ish °C. You really don't want to get to a point where your engine is in thermal runaway as then if your auxillary fans are not working correctly you will need quite a lot of revs to draw enough air in using the viscous fan to cool the engine down.

Dave!
 
I may have some free time when i'm back in the UK late September to pop over with mine and compare. It should never reach 120°C in the UK at all imo, the conditions and temps are just not high enough for that to happen on a working system.

Firstly i'd confirm that they are the temperatures you are getting by using an infra red thermometor on your bottom hose. Your fans use a seperate sensor in the front of the engine so they may be seeing a lower temperature than your gauge sees.

Dave!
 
Hell I may aswell make it 4 in a row :eek:

I believe if you pull off the fan resistor connection then both fans will come on at full speed, a good way to check the fan operation.

Dave!
 
Hell I may aswell make it 4 in a row :eek:

I believe if you pull off the fan resistor connection then both fans will come on at full speed, a good way to check the fan operation.

Dave!

where is this located
 
Shamelessly stolen from K6JRFs page.

http://pages.prodigy.net/jforgione/CTS_Mod.jpg

Take off the plastic cover infront of your airbox (The large oblong one) and you will see the sensor.

Be careful removing it though as they can be tight.

Dave!

OK, will check that once I get the new viscose coupling on, the new modern day part is different from the old part, its not as wide and does not come with the black plastic cover. have just put it on and because its narrower, theres more bolt sticking out the end when you bolt it on so I cannot get it tight enough now. When tight theres paly in the coupling and fan because its not tight/flusk up to pulley......aaaahhhh!!!

nowts easy is it.

Just spoke to Ian Walker on phone and he says cut the bolt down??!!

Paddy 07986 373236
 
Rather than cut the bolt down I'd be inclined to add a washer as a spacer, in case the viscous pulley isn't the correct one.
 
Rather than cut the bolt down I'd be inclined to add a washer as a spacer, in case the viscous pulley isn't the correct one.

Yep, far better idea.

Aslong as it locates centrally so is balanced then some washers will be fine.

I will not go into my usua rant about pattern parts :crazy:

Dave!
 

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