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| King_GH Extreme Veteran Date registered: Oct 2011 Location: London Vehicle(s): 95 G300 RHD Posts: 324  | Where’s the fan switch/thermostat on 1995 m103 Gas engine? I believe mine’s defective as the fan is not kicking in but I can’t figure out where it is. I can see the one connected to the water tank but not the one for the fan. Any help will be useful! | ||
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| King_GH Extreme Veteran Date registered: Oct 2011 Location: London Vehicle(s): 95 G300 RHD Posts: 324 | Re: Where’s the fan switch/thermostat on 1995 m103 Gas engine? Oh dear found it now. It's on the opposite side of the spark plugs right after the little vaccum regulator thingy .... got to get that replaced. Edited by King_GH 5/15/2018 3:54 PM | ||
| #239163 - in reply to #239162 |
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| AlanMcR Expert Date registered: Apr 2006 Location: US, CA, Los Altos Vehicle(s): G300DT E300DT 230SL Posts: 3500  | RE: Where’s the fan switch/thermostat on 1995 m103 Gas engine? King_GH - 5/15/2018 11:04 AM I believe mine’s defective as the fan is not kicking in but I can’t figure out where it is. I can see the one connected to the water tank but not the one for the fan. Any help will be useful! If you are talking about the fan between the radiator and the engine, that is mechanically driven. In the hub there is a thermostatically controlled hydraulic system that locks up when it gets too hot. The typical problem is that the seals give out and the hydraulic fluid leaks out. Refilling it is, at best, a short term fix. The fan in front of the radiator is driven by the AC system, and on some models it is also triggered by extreme overheating +130C.
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| #239164 - in reply to #239162 |
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| King_GH Extreme Veteran Date registered: Oct 2011 Location: London Vehicle(s): 95 G300 RHD Posts: 324 | RE: Where’s the fan switch/thermostat on 1995 m103 Gas engine? AlanMcR - 5/15/2018 7:55 PM King_GH - 5/15/2018 11:04 AM I believe mine’s defective as the fan is not kicking in but I can’t figure out where it is. I can see the one connected to the water tank but not the one for the fan. Any help will be useful! If you are talking about the fan between the radiator and the engine, that is mechanically driven. In the hub there is a thermostatically controlled hydraulic system that locks up when it gets too hot. The typical problem is that the seals give out and the hydraulic fluid leaks out. Refilling it is, at best, a short term fix. The fan in front of the radiator is driven by the AC system, and on some models it is also triggered by extreme overheating +130C.
Alan the issue is why does it have to go that high before being triggered? Surely it could use some cooling before it gets to such extreme temperatures. Are we then saying that it's possible that mine isn't broken because I could never sit and watch it climb that high as I intervene by increasing the RPM to get the fan working faster. | ||
| #239166 - in reply to #239164 |
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| gerryvz Extreme Veteran Date registered: Apr 2014 Location: Annapolis, MD Vehicle(s): 1994 G320, 1989 560SEC, 1994 E500 (W124) Posts: 336 | Re: Where’s the fan switch/thermostat on 1995 m103 Gas engine? The electrically driven fan in front of the radiator is a two-stage fan. If your truck has A/C, then the low (first) setting is on to increase airflow across the radiator and condenser to assist the A/C in cooling. If the temperature gets above I believe 107 or 108C (about halfway between the 100C and 120C marks on the temp gauge), then the second stage will go on until things cool down. This electrically driven fan is controlled by the coolant temp sensor in the intake manifold, near the water pump. (And the first stage is switched on by the A/C circuit if A/C is running). You cannot control the operation of the electric fan. Separately, as AlanMcR mentions, the second system is the mechanically driven fan clutch, directly behind the radiator. This has a bi-metallic strip on the face of the clutch, which is temperature sensitive. The fan clutch is filled with fluid, and it can and does leak out. It's very common on these fan clutches for the M103 and M104 engines (which share the same clutch). Operation of the fan clutch is both heat- (bi-metallic strip) and RPM driven. When the bi-metallic strip heats up, it stiffens and engages the fan clutch. This engages the clutch (the fluid inside provides resistance). You will hear the fan clutch engage, audibly, with a "whoosh" sound and it sounds like a wind tunnel. The fan clutch is designed to pull in A LOT of air -- it is demonstrably more efficient than any electrically driven fan could be in the same physical space. Generally the fan clutch will engage when engine temperatures near 100C (the middle hash mark between 80 and 120) and the RPM of the engine is 2000-2500 or higher. Fan clutch failure is quite common - it was one of the very first things I did when I got my G320 (M104) back in 2014. Mine had failed. Replacements are shared with the M103 and M104 engines in passenger cars, and a Behr is the best unit to get. You can get them cheaply on the aftermarket -- they are ~$100 give or take from common aftermarket parts vendors like AutohausAZ.com and others. Perhaps even Amazon.com. It's a bit of a PITA to replace the clutch as space is tight, although on the G there is more room than on the passenger cars. For passenger cars you need a special tool (a bent coat hanger can suffice in a pinch, but the tool is optimal) to place in the hole behind the clutch to prevent the hub from rotating while you unbolt the single Allen bolt that holds the fan to the hub. MB makes a special "stubby" socket to replace it, although I think on a G you can use a normal Allen socket. For the G, you don't have to use the special tool to hold the hub, because you can wedge a screwdriver and hold the hub while loosening the clutch bolt. If I remember correctly, I did a HOW-TO on the replacement of the fan clutch: https://www.500eboard.com/forums/showthread.php?t=6152 Hopefully this illustrated HOW-To will help. It's not a horrible job. Cheers, Gerry | ||
| #239167 - in reply to #239162 |
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| DUTCH Administrator Doppelgänger Date registered: Apr 2006 Location: US, GA, Atlanta Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter Posts: 9963  | Re: Where’s the fan switch/thermostat on 1995 m103 Gas engine? gerryvz - 5/15/2018 10:19 PM Hopefully this illustrated HOW-To will help. It's not a horrible job. Cheers, Gerry With the right tool, KD Tools KDT3472 3 pc Fan Clutch Wrench Kit, it's a 10 minute job. The following was used on my M113 G500. My Indie mechanic said it was so much better than the MB factory tool that he bought one to use in his shop. https://www.toolsource.com/fan-clutch-c-1321_92_95/fan-clutch-wrench... | ||
| #239177 - in reply to #239167 |
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| King_GH Extreme Veteran Date registered: Oct 2011 Location: London Vehicle(s): 95 G300 RHD Posts: 324 | Re: Where’s the fan switch/thermostat on 1995 m103 Gas engine? Thanks all, it's all making sense. I remember my mechanics replaced the fan clutch the last time it failed. Now I can't vouch for whatever one unit they used. However I remember hearing the whoosh sound and complaining that the noise made my car sound like a Nissan Patrol! I do realise now that this sound has ceased and I have never heard it again perhaps a few weeks after the installation. I will need to test the fan clutch to determine if it's broken. When I spun it it did feel stiff though. | ||
| #239184 - in reply to #239162 |
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| AlanMcR Expert Date registered: Apr 2006 Location: US, CA, Los Altos Vehicle(s): G300DT E300DT 230SL Posts: 3500 | RE: Where’s the fan switch/thermostat on 1995 m103 Gas engine? King_GH - Alan the issue is why does it have to go that high before being triggered? Surely it could use some cooling before it gets to such extreme temperatures. Are we then saying that it's possible that mine isn't broken because I could never sit and watch it climb that high as I intervene by increasing the RPM to get the fan working faster. That sensor is just a last-ditch fallback. I don't like the high setting either. If your G uses this part: A0075455824 ORIGINAL three pin temperature sensor in hose (110/130C too hot) Then you can replace it directly with this part to lower the setpoint: A0065454224 three pin temperature sensor in hose 100/110C (to replace 110/130C) I did this and I can say that on hot days the front fans will kick in on occasion, even though the display gauge hasn't hit 100C. The top hose sensor is sitting directly in the hot outflow from the head which is hotter than the average temperature of the engine. | ||
| #239189 - in reply to #239166 |
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| King_GH Extreme Veteran Date registered: Oct 2011 Location: London Vehicle(s): 95 G300 RHD Posts: 324 | RE: Where’s the fan switch/thermostat on 1995 m103 Gas engine? AlanMcR - 5/17/2018 7:08 PM King_GH - Alan the issue is why does it have to go that high before being triggered? Surely it could use some cooling before it gets to such extreme temperatures. Are we then saying that it's possible that mine isn't broken because I could never sit and watch it climb that high as I intervene by increasing the RPM to get the fan working faster. That sensor is just a last-ditch fallback. I don't like the high setting either. If your G uses this part: A0075455824 ORIGINAL three pin temperature sensor in hose (110/130C too hot) Then you can replace it directly with this part to lower the setpoint: A0065454224 three pin temperature sensor in hose 100/110C (to replace 110/130C) I did this and I can say that on hot days the front fans will kick in on occasion, even though the display gauge hasn't hit 100C. The top hose sensor is sitting directly in the hot outflow from the head which is hotter than the average temperature of the engine. Brilliant idea, except I have just replaced it with the original and watched it climb to a 100 and kicked in. I was quite pleased but your idea seems much better. My connector to the swich is just a single pin with a red neck. How can I retro fit? Could there be a more suitable one I could use? Also checked your part, I think your base is about half the size of mine in diameter. I found this one https://www.ebay.co.uk/itm/Radiator-Fan-Temperature-Switch-Behr-TSW-... It kicks in at 90. Perfect! that seems better. I got mine direct from MB. I need to cross check first if this one kicks in lower I'll get this and replace it. Edited by King_GH 5/20/2018 6:29 PM | ||
| #239213 - in reply to #239189 |
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| King_GH Extreme Veteran Date registered: Oct 2011 Location: London Vehicle(s): 95 G300 RHD Posts: 324 | Re: Where’s the fan switch/thermostat on 1995 m103 Gas engine? Whilst still on the subject of cooling, my fan clutch comes on immedeatly with the engine at one speed and this speed is maintained and never increased until the gas pedal is pressed to increase the RPM. It does switch of immedeatly with the engine and there's no play. I remember that it used to be very loud when the car was moving - I can't hear that noise again. The last time it was replaced the temp was always exactly on the 80 line. However these days even on a cold day the gauge sits on top of the 80 mark. It may appear to be okay as it's just a slight move up however when you start idling in traffic you will soon conclude like I have that there must be something not right with that. | ||
| #239214 - in reply to #239184 |
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| King_GH Extreme Veteran Date registered: Oct 2011 Location: London Vehicle(s): 95 G300 RHD Posts: 324 | RE: Where’s the fan switch/thermostat on 1995 m103 Gas engine? King_GH - 5/20/2018 10:01 PM AlanMcR - 5/17/2018 7:08 PM King_GH - Alan the issue is why does it have to go that high before being triggered? Surely it could use some cooling before it gets to such extreme temperatures. Are we then saying that it's possible that mine isn't broken because I could never sit and watch it climb that high as I intervene by increasing the RPM to get the fan working faster. That sensor is just a last-ditch fallback. I don't like the high setting either. If your G uses this part: A0075455824 ORIGINAL three pin temperature sensor in hose (110/130C too hot) Then you can replace it directly with this part to lower the setpoint: A0065454224 three pin temperature sensor in hose 100/110C (to replace 110/130C) I did this and I can say that on hot days the front fans will kick in on occasion, even though the display gauge hasn't hit 100C. The top hose sensor is sitting directly in the hot outflow from the head which is hotter than the average temperature of the engine. Brilliant idea, except I have just replaced it with the original and watched it climb to a 100 and kicked in. I was quite pleased but your idea seems much better. My connector to the swich is just a single pin with a red neck. How can I retro fit? Could there be a more suitable one I could use? Also checked your part, I think your base is about half the size of mine in diameter. I found this one https://www.ebay.co.uk/itm/Radiator-Fan-Temperature-Switch-Behr-TSW-... It kicks in at 90. Perfect! that seems better. I got mine direct from MB. I need to cross check first if this one kicks in lower I'll get this and replace it. So having installed this Behr switch. I can hear the fan kicking in at 90C. Makes a lot of sense to me. It is my opinion that the fan clutch is dead even though it feels quite stiff. The fan clutch seems to run at one speed regardless of the temperature. At no point do I hear it scream like it used to when it was first installed. My theory is that the garage that did the installation used a very cheap one and I failed to notice it until summer. I'm changing it for a SACHS one. One thing I noticed was that there is hardly any space available for the 22 mm socket to remove it. The only way was to open up the engine cover and then race against the water trying to get into the engine when the switch is unscrewed! Easy one really I think if you're in a hot climate a 90C fan switch should be the standard not 100C. Edited by King_GH 5/26/2018 1:11 AM | ||
| #239244 - in reply to #239213 |
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