Low temperature thermoswitch

[joris_andriesse 8]

Hi all,

Since I'm going to place 2 Spal fans to my radiator, I also want to renew/upgrade (a little) the way the are being controlled. I was thinking about a 3 pin thermoswitch, two fan relais and then 1 or 2 fans kicking in depending on the temp.

But now, which thermoswitch to choose, since I do read on several forums that the best place to located the thermoswitch would be on the outlet side of the radiator. Reason for that is that your coolant temp will always be high on the inlet side of the radiator, but in most cases the airflow true the radiator, while driving, should be sufficient for cooling the cooling fluid. Only when in traffic jam/ city/ traffic light etc. there is no airflow and your cooling fluid temp will still be to high when leaving the radiator and that should be the moment the fans kick in.

The common 205/MI16 thermoswitches work on a +/- 90-100 degrees range, but that's on a inlet temp based and would be to high for using it on the outlet side. On the outlet side (so going into the engine again) I would think that you would like to have a temp of lets say max 70 degrees, correct? Does any of you have experience with using a lower temp thermoswitch, and if so, which one?

 

[petert 586]

70 is too low. You could use a diesel switch but you need to match the thermostat, otherwise the fans will never turn off.

[Thijs_Rallye 87 4 Cars]

18 hours ago, joris_andriesse said:

since I do read on several forums that the best place to located the thermoswitch would be on the outlet side of the radiator.

The engine out temperature is way more important than the radiator temperature out imho. Personally I wouldn't deviate from that position.

 

When an engine is calibrated in an OEM environment these engines are loaded with additional sensors to evaluate cooling performance in and around the engine and engine components. Most heat rejection will occur at the cylinder head and the fire ring of the liner, most cooling requirements are driven from the data measured there.

 

[joris_andriesse 8]

3 hours ago, Thijs_Rallye said:

The engine out temperature is way more important than the radiator temperature out imho. Personally I wouldn't deviate from that position.

 

When an engine is calibrated in an OEM environment these engines are loaded with additional sensors to evaluate cooling performance in and around the engine and engine components. Most heat rejection will occur at the cylinder head and the fire ring of the liner, most cooling requirements are driven from the data measured there.

 

"The engine out temperature is way more important than the radiator temperature out imho" depends where you are going to use the info for. If we are talking about a temp sensor, to be used for input for the ecu and/or for showing the temp on a dashboard gauge, you are right.
But I'm talking about a temp switch to be used for controling the fans. I think that you might have an advantage controling the temp of the coolant before it goes into the engine again, above reacting on it when it comes out the engine to hot. I think that you than measuring 1 coolant cycle ahead and because of that having the radiator as a coolant buffer.

 

 

7 hours ago, petert said:

70 is too low. You could use a diesel switch but you need to match the thermostat, otherwise the fans will never turn off.

I'm talking about the outlet, where the coolant goes back into the engine.
On the inlet side your right, there the temp switch temp should be above thermostat temp, since coolant temp will almost be like the temp in the engine head. On the outlet side of the radiator however, you want the temp to be much lower (which is the function of the radiator, before it goes back into the engine again. Measuring on the outlet side with, for example, a 82-65 degrees temp switch (I just found such a one online) is possible and won't make your fans run all the time. Because coolant will be at 88 degrees when entering the radiator, when your radiator works (airflow going true), the temp will/must be on the outlet side much lower so the fans won't turn on. When there is no airflow, the coolant won't cool down, will be higher than 82 degrees arriving at the outlet side and your fans will kick in.

 

[Thijs_Rallye 87 4 Cars]

56 minutes ago, joris_andriesse said:

But I'm talking about a temp switch to be used for controling the fans.

I understand what you mean, but if you route it that way you will use a uncontrolled device (the radiator) before your measurement input. So the system can (and will) influence itself which is not the best control strategy imho. Don't fix what isn't broken.

 

 

[Richie-Van-GTi 71 2 Cars]

You need to measure the temperature coming into the radiator, not out of it. You are disregarding the efficiency of the radiator with your plan, you may have coolant coming in at 120 degrees but be unaware as the radiator is very efficient, result would be damage to the engine as its too hot. There is a reason manufacturers put it on the inlet.

 

As for 2 fans, in my racecar i have twin fans, both on a permanent live with the earths running through a twin temp switch from a 306 so one acts as a low and the other as a high. Works perfectly

[joris_andriesse 8]

2 hours ago, Richie-Van-GTi said:

You are disregarding the efficiency of the radiator with your plan, you may have coolant coming in at 120 degrees but be unaware as the radiator is very efficient, result would be damage to the engine as its too hot. 

I do not understand this. With my plan I think I actually have more insight in the efficiency of the rad, because I will be measuring at the outlet side and not the inlet side and I therefore know whether the temp, going back into the engine, is cool enough or will need some extra cooling by the fans.

 

2 hours ago, Richie-Van-GTi said:

As for 2 fans, in my racecar i have twin fans, both on a permanent live with the earths running through a twin temp switch from a 306 so one acts as a low and the other as a high. Works perfectly

That would be my second option, using a Facet Temp switch with 92-87 97-92 degrees switch temps. I only do not want the rad power going true the temp switch, so I will be using two relais.