Temp switch - Mercedes-Benz Forum
 
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post #1 of 9 (permalink) Old 07-17-2019, 06:20 AM Thread Starter
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Temp switch

Ok just watched the new video in installing a new temp unit to bring on the aux fan. I know many of us are concerned about high running temps and have done various things. I for one added the resistor on the temp sending unit to start the aux fan running temp to 95 c instead of 100. But why done we just get a different temp sending unit to bring the aux fan on at the temp we want. They are all over the place and cost is about $20. I might have to change the threads on the goose neck but that is not a big deal. I likely would do an 85 c one. Can anyone see the negative except the fan will run a lot more and wear out?
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post #2 of 9 (permalink) Old 07-17-2019, 06:48 AM
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I guess somewhat more draw on the alternator, which increases drag on the engine a wee bit. Which in turn produces some small amount of extra heat.

I wonder if it would make more sense to have it coming on at 90, or 95 even. Rather than having it run so much.

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post #3 of 9 (permalink) Old 07-17-2019, 06:59 AM
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You want to make sure the thermostat has time to open completely before the fan kicks in, otherwise you will have the two actually working at cross purposes.
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post #4 of 9 (permalink) Old 07-17-2019, 10:02 AM Thread Starter
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Ok makes sense. T stat is supposed to open at 80 so a temp switch could be 85 to 90 I guess. I just think putting a sensor in like this is easier than doing the resistor, etc. will try one and let you know since I have on order a 71c stat just to see what it does. As I mentioned a thread ago the choke point could be the pump, the radiator, the sensor, fan clutch, clogged radiator fins etc.

So far no radiator mgf has provided info on btu rejection
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post #5 of 9 (permalink) Old 07-20-2019, 11:37 PM
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Originally Posted by Stutz View Post
Ok just watched the new video in installing a new temp unit to bring on the aux fan. I know many of us are concerned about high running temps and have done various things. I for one added the resistor on the temp sending unit to start the aux fan running temp to 95 c instead of 100. But why done we just get a different temp sending unit to bring the aux fan on at the temp we want. They are all over the place and cost is about $20. I might have to change the threads on the goose neck but that is not a big deal. I likely would do an 85 c one. Can anyone see the negative except the fan will run a lot more and wear out?
One negative I see is the less likelihood of passing a smog inspection. A hotter running engine burns more NOx emissions than a cooler running engine.
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post #6 of 9 (permalink) Old 07-24-2019, 03:56 AM Thread Starter
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I ordered this from ebay and with the cost ($6.00) its a no brainer to try. The threads are correct too. Basicslly you can find any temp one you want to turn the fan on. Since I have a lower tstat in now it should not be an issue. I will install this once it gets here and report the results. I will have to change the connectors but for now to keep it original until I decide if it works or not will rig something temporary

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post #7 of 9 (permalink) Old 07-24-2019, 06:37 AM
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post #8 of 9 (permalink) Old 08-11-2019, 08:37 AM Thread Starter
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Finally tackled this today and here are some pics and comments.

1) I wanted to leave things mostly stock looking for now so I made things that could be put back. I used some mercedes plug pins I had laying around so the pins would fit into the original sensor plug.
2) I removed the resistor that I had installed which brought the electric fans on at 95 degrees
3) This sensor fit right on and cost about $6.00 shipped
4) For the sensor I simply used female spade ends.

This is supposed to turn on the fans on at 85 but if one wanted to select another temp one could simply order that sensor.

I picked 85 since the T stat I just put in was rated for 71c and I had really hoped to get things to run at about 80. Yesterday it was running at 90 so not there yet.

This week is dream cruise week and its hot out so this will be a good test since there is a lot of stop and go traffic.

Stay tuned
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post #9 of 9 (permalink) Old 08-11-2019, 10:28 AM Thread Starter
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Nooo. I should have known Mercedes would have some special sauce. I assumed the new temp switch was a simple on off but there is a difference between the old and new somewhere. When I put the new one on the fan runs constantly even though the new temp sending unit shows no continuity. There must be some slight resistance on the new one that the system registers. Back to the drawing board I guess. I knew it was too easy.
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