Best fan relay for a 200tdi electric fan

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Tomaco1

Well-known member
Which would be better?

On at 195, off at 175 degrees

or

On at 185, off at 165 degrees
 

Red90

Well-known member
Both are too low, IMO. The thermostat does not start to open until 190. My fan comes on at 200.
 

RDavisinVA

Technical Excellence Contributor
What you're asking for is a thermal switch that will control a relay.
We have them.
 

Tomaco1

Well-known member
I have the allisport rad with the sender in the center. I have the 195 spal sender which is working sporadically, I’m going to check the wiring today. But when looking to order a new one saw some options and was also thinking what Red said, how close 195 is to the thermostat temp.
 

rocky

NAS-ROW Addict
If you have twin electric fans, could you set them up to come on at different temps?
 

Red90

Well-known member
If you have twin electric fans, could you set them up to come on at different temps?

The "typical" path for people that go that route is to use a Volvo dual fan relay with a BMW dual temperature fan switch. Both common and easy to source used or new and built with proper OEM quality to live in an engine bay. Various writeup around with a quick Google

The other thing, IMO....is to control based on actual engine temperature, not at some point in the rad or the rad outlet. This provides better (less swing) control of the engine temperature, which is the primary goal for this control loop. I run my sensor on one of the ports just above the thermostat. You can drill and tap them.
 

javelinadave

Administrator
Staff member
To answer your question I would go with the lower temp relay. As temps swing up you would want to get air moving before things get to hot. In the winter they will probably never turn on. In the summer, a little cooler is better than a little warmer. They are also $32 each so buy one of each and save on shipping.;)
 

Red90

Well-known member
To answer your question I would go with the lower temp relay. As temps swing up you would want to get air moving before things get to hot. In the winter they will probably never turn on. In the summer, a little cooler is better than a little warmer. They are also $32 each so buy one of each and save on shipping.;)

A 185 switch will cause the fan to be on continuously as the engine temperature should never be below 190.
 

javelinadave

Administrator
Staff member
I ran a 185 degree t-stat with zero issues, A/C running and a mechanical fan in 120+ degrees. I don't agree with your "never be below 190" but whatever rocks your world.
 

Red90

Well-known member
I ran a 185 degree t-stat with zero issues, A/C running and a mechanical fan in 120+ degrees. I don't agree with your "never be below 190" but whatever rocks your world.

The stock thermostat is 190 F. That means that it starts to open at 190 F. If the engine temperature is below 190, then the thermostat is leaking. You want your electric fan control (on engine temperature) to be at a temperature higher than when the thermostat starts to open or else it will stay running. I'm not sure what saying you successfully used a mechanical fan has to do with the choice of an electrical fan control switch.
 

javelinadave

Administrator
Staff member
The OP asked a question and I gave him my opinion.
Phoenix to Alaska and back with no issues is my success. Trails throughout the Southwest in hot, cold and freezing weather is my success. All with a 185 degree thermostat. You getting grocery and coffee may be your testbed which may work for you but as I said, whatever rocks your world John. If you looking for an online fight, bring it! I’m home bored out of my mind and stopped drinking coffee two days ago.
 

Red90

Well-known member
Fight? I'm provide logic to back my point of view and explaining why your advice does not make sense. It is a discussion over a technical item. You have not talked to the science in any way whatsoever.

Yes. I only drive my truck to the grocery store. It is not required for you to be an asshole. If anyone is bringing emotion into this thread, it is 100% on you.
 

javelinadave

Administrator
Staff member
Science and fact
The 200/300Tdi motors came with a mechanical fan and a 190 degree thermostat. They work and don't need to be changed.
If a vehicle is running hot it is a mechanical issue and an electric fan is a band-aid as is Wetter Water.
A temp difference on a non ECU engine of 5 degrees isn't going to effect its performance, fuel economy or anything else for that matter.
Under load while moving slowly (off-roading, local towing, etc) the extra 5 degree margin gets coolant flowing that much sooner so the entire mass of the engine, starting to shed heat sooner.

If I recall you once posted on the other forum that you had a Ford Taurus fan that would cool so fast that you could see the temp gauge needle move the second it came on. People hopped on your ass about that bit of "science".

As for your "asshole" comment, we don't name call here. We are all expected to act like adults.
 

Red90

Well-known member
Science and fact
The 200/300Tdi motors came with a mechanical fan and a 190 degree thermostat. They work and don't need to be changed.
If a vehicle is running hot it is a mechanical issue and an electric fan is a band-aid as is Wetter Water.
A temp difference on a non ECU engine of 5 degrees isn't going to effect its performance, fuel economy or anything else for that matter.
Under load while moving slowly (off-roading, local towing, etc) the extra 5 degree margin gets coolant flowing that much sooner so the entire mass of the engine, starting to shed heat sooner.

Nothing in the above has anything to do with the topic of this thread. The topic is what temperature to turn the fan on and off at.

As for your "asshole" comment, we don't name call here. We are all expected to act like adults.

You are the one that threw the insult first. You behave like an adult and I will follow suite.

You getting grocery and coffee may be your testbed which may work for you but as I said, whatever rocks your world John.
 

javelinadave

Administrator
Staff member
So saying somebody drives a grocery getter (even if it is true) is an insult? Interesting! Sorry I hurt you feelings John. Next time I'm in your neck of Canada I'll buy you a breakfast at Timmy's
Let end this and get back on track with this thread.
@Tomaco1 , For $32 buy one of each and see what works best for you. I'm sure plenty of people run one or the other with no complaints.
 

Red90

Well-known member
Give me a break. You intended the comment as a direct insult and you know it. Standing here denying it speaks volumes.
 
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