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+--- Thread: Radiator fan switch: what temperature? (/showthread.php?tid=7785)
Radiator fan switch: what temperature? - frans-c - 06-19-2017
I need to urgently sort out my radiator fan for the C250TD (I replaced my non-working viscous fan and twin-auxiliary fans with a single 17" Tripac two-speed fan).
I've had excellent results installing a temperature switch at the bottom radiator hose of my old 280E. I want to do something similar again now, using a two-speed temperature switch from a BMW for my two-speed radiator fan.
There are two (stage 1) temperature variations: the first temperature switch switches on at 80°C and off at 75°C, the second switches on at 90°C and off at 85°C.
My thermostat is rated at 80°C. Should I use the first or second temperature switch? My logic tells me that the coolant at the bottom of the radiator is quite cool, so the lower temperature switch should work. On the other hand, I don't want the fan to work overtime.
I'd prefer the engine to operate in the 80°C - 85°C temperature range.
My online searches suggest a switch slightly higher than the thermostat's temperature - I'm just concerned that the engine will run a bit warmer than what I'd want.
RE: Radiator fan switch: what temperature? - Petar - 06-19-2017
My opinion: if your thermostat is fully open at 80 *C your fan should turn off at say 82 *C and kick on at say 87 *C. Second stage should turn on somewhere between 90 and 100 *C
No point to have the fan on if the thermostat is not fully open. I bet once turned on it'll never shut off if the turn off temp is higher than the thermostat opening temp
RE: Radiator fan switch: what temperature? - frans-c - 06-19-2017
(06-19-2017, 03:09 PM)Petar My opinion: if your thermostat is fully open at 80 *C your fan should turn off at say 82 *C and kick on at say 87 *C. Second stage should turn on somewhere between 90 and 100 *C
No point to have the fan on if the thermostat is not fully open. I bet once turned on it'll never shut off if the turn off temp is higher than the thermostat opening temp
Thanks. The more I think about it, the more the higher temperature switch makes sense.
RE: Radiator fan switch: what temperature? - AlanMcR - 06-19-2017
The thermostat will determine when to pump water through the radiator (80C). The radiator's job is to pull that temperature down as far as possible. If the air isn't moving fast enough then the exit temperature will rise.
So, measure the temperature at the exit of the radiator. If that comes close to the thermostat temperature (80C), then you know the radiator needs help. Perhaps turn on the "low" at 75C and off at 70C, measured at the radiator exit. Then turn on the "high" at 80C, off at 75C.
RE: Radiator fan switch: what temperature? - Hario' - 06-21-2017
I have a on @87 off @82 celcius switch because it was the only one which was M14x1.5 thread to fit into the blanking plug on the cylinder head by #6 glow plug, not sure if 605 has this though.. Like so:
![[Image: temp%20switch%201.jpg]](http://s1250.photobucket.com/user/Mercedes_Power/media/temp%20switch%201.jpg.html)
![[Image: temp%20switch%202.jpg]](http://s1250.photobucket.com/user/Mercedes_Power/media/temp%20switch%202.jpg.html)
RE: Radiator fan switch: what temperature? - Petar - 06-21-2017
@frans-c
In your thread you had a W210 CDI variable speed fan, curious to know why you didn't use it ?
The fan clutch on my C250TD is completely dead and I can't decide should I buy a new fan clutch, or buy a W210 CDI fan. How many pins does the fan connector have ?
RE: Radiator fan switch: what temperature? - frans-c - 06-22-2017
The fan I bought was for the V6 engine - it was way too thick to fit between pulleys and radiator. So I had to make another plan with the 17" Tripac fan.
RE: Radiator fan switch: what temperature? - frans-c - 06-22-2017
(06-21-2017, 12:54 PM)Hario\ I have a on @87 off @82 celcius switch because it was the only one which was M14x1.5 thread to fit into the blanking plug on the cylinder head by #6 glow plug, not sure if 605 has this though.Yup, I've actually already screwed in a two-speed W124 300E fan switch in there, but never got around to wiring it. However, I've come to realise that its temperature rating of 100°C on, 95°C off is too high for my liking. My experience with my old W123 280E, where I did something similar, was that a fan switch screwed inside the head results in the fan running too long at a time. Connecting it at the radiator outlet resulted in way much better temperature control and much shorter fan operation.
RE: Radiator fan switch: what temperature? - Hario' - 06-23-2017
(06-22-2017, 01:09 PM)frans-c(06-21-2017, 12:54 PM)Hario\ I have a on @87 off @82 celcius switch because it was the only one which was M14x1.5 thread to fit into the blanking plug on the cylinder head by #6 glow plug, not sure if 605 has this though.Yup, I've actually already screwed in a two-speed W124 300E fan switch in there, but never got around to wiring it. However, I've come to realise that its temperature rating of 100°C on, 95°C off is too high for my liking. My experience with my old W123 280E, where I did something similar, was that a fan switch screwed inside the head results in the fan running too long at a time. Connecting it at the radiator outlet resulted in way much better temperature control and much shorter fan operation.
Yeah I thought you'd say that, interestingly it is right next to the stock temperature sensor.
You need to get a w124 fan switch from a diesel then!
RE: Radiator fan switch: what temperature? - AlanMcR - 06-23-2017
The stock temperature sensor is there to tell the ECU (and the driver) what the engine temperature is. That is a lagging indicator of temperature. The fan needs to know whether the radiator is running out of cooling capacity at the current air flow rate.
RE: Radiator fan switch: what temperature? - Petar - 06-23-2017
Makes sense. After all stock viscous fan coupling senses heat from the hot air that exits the rad and it works great. Engine temp seems to be pegged while the fan turns on or off as necessary.
RE: Radiator fan switch: what temperature? - frans-c - 06-24-2017
I think I've found a perfectly rated two-speed Mercedes-Benz switch:
https://www.rexbo.eu/behr/temperature-switch-radiator-fan-tsw35?c=100334&at=350
My question still remains, though: should I install it in the spare sensor location in the cylinder head, or at the radiator outlet...?
RE: Radiator fan switch: what temperature? - barrote - 06-24-2017
U can use both places!!!
2 situations apply:
If the switch is rated below 80° for closing circuit it must be placed at the radiator. If is above 85° is suitable for the head.
In any case make sure the spare place at the head has contact with coolant, otherwise it will have defective operation. U can drill a hole to get contact with coolant.
RE: Radiator fan switch: what temperature? - Hario' - 06-24-2017
(06-24-2017, 03:30 AM)frans-c I think I've found a perfectly rated two-speed Mercedes-Benz switch:
https://www.rexbo.eu/behr/temperature-switch-radiator-fan-tsw35?c=100334&at=350
My question still remains, though: should I install it in the spare sensor location in the cylinder head, or at the radiator outlet...?
tHAT sensor looks good.
YEs the spare fitting in the head contacts coolant, trust me it squirts out if its still warm...
RE: Radiator fan switch: what temperature? - frans-c - 06-24-2017
(06-24-2017, 04:47 PM)Hario tHAT sensor looks good.Hmm, I'm just a little worried that the 81°C cut-off temperature for the low-speed will never be reached if the sensor is installed inside the head. I reckon the outlet side of the radiator may work a bit better.
YEs the spare fitting in the head contacts coolant, trust me it squirts out if its still warm...