Relationship between thermostat temp and fan swith temp

[wolf_walker]

Interested in hearing opinions/experience. 

I have run 80 and 87C thermostats, and never had to replace a fan switch.

Thoughts?

[8v-of-fury]

I do believe the fan switch is several degrees higher than whatever thermo the car should have.

IE. You don't want an 87 fan switch coupled with an 87 thermostat, as the fan would be coming on at the same time as the rad was just starting to get flow. This would have your rad fan on pretty much the entire time the engine was up to temps.

Now I do not know what temps fan switches run at, as I dont have a working one lol. I have mine manually switched. The 88 works, but I dunno what temp is in there. I know I have an 87 stat in my car, I can see the thermostat open fully at around 90C because without turning the fan on and the car not moving I can see the temps drop to below 85 just from the radiator starting to move the cooler coolant through the system.

So, as long as your fan comes on by 3/4 gauge she's good to go. You should only see those temps if you are beating on it at low speeds, or if the car is sitting idling.

[CRSMP5]

i guess i am stupid...

80*c thermo = cooler running.. how is it cooler if fan no on till 92*c  why else add 80*c thermo....

87*c stat = 92*c thermo
80*c = 87*c
72*c = 80*c

i want my crap cool down road and in town..

[8v-of-fury]

OP probably has the 92C fan switch then..

[wolf_walker]

When the vehicle is in motion, the fan is "on" in spirit, since there is airflow, lots of it.   Too much, they put those flaps on the fan shroud. 
 
I have in the past with both add-on fans and SEM setups been able to dial in a stable temprature, I don't like to see
fluctuation over too great a range.  VW-D's always seemed to fluctuate quite a bit, and I don't know that this is 
especially undesirable, but I can't see a reason it would be better than it staying stable.
Can anyone else?
 
Diesel's don't like to run cold, and I have seen VW-D's in cold clmates have trouble with an 80C t-stat.
More than once.
 
The stock, original, NA t-stat (and TD though the PN is different and I'm not sure why?) from back in the early 80's is listed as 
"87C-102C" per ETKA.
It starts to open at 87(188F), and is fully open by 102(215F).
This makes me think VW intended these guys to run at about 200F.
 
The fan switch, for a single speed fan for simplicities sake, is 175959481 and there is no temp note in 
ETKA like the 3 prong one has.  I also see a lot of descrephency online via the usual vendors for the correct
2 prong switch but that isn't uncommon.  I'm guessing it kicks at 220F, just above the full-open spec for the
t-stat, which jives with my observation and as 8V said, about 3/4 of the gauge.
 
I believe I'd prefer it to kick the fan on about 10F sooner/cooler.   
I don't see any reason to let it get to 
220F.
 
Does anyone else?

[8v-of-fury]

Saves fan life, and unnecessary load on the engine really.

How often does it get to the point the fan comes on? Not often right? As soon as you start driving, it immediately starts to drop off.

The only time the fan in the 88 (fully stock system) ever comes on is when it has sat and idled with absolutely no air flow in the summer. I have not heard the fan at all this winter, even with extended idle times to keep heat when it is below freezing.

I can sit and idle my 1.9 for ever, and it will only slowly creep up to near 200.. turning on the cabin fan to 2 brings it right back down sufficiently.

I don't think you have to worry about running too cold anywhere south of Sacramento! haha.

[wolf_walker]

Good point, and true.

Sent from my SCH-I535 using Tapatalk 2

[wolf_walker]

I think I'd give up some fan life to keep the temp a little lower though personally.  The big ole single speed guys never seem to fail anyway.

Do you know off hand what teh diff is between the TD and NA t-stat is? Temp is the same, I thought the pump and housings and all were the same too.

[8v-of-fury]

Temperature wise? There is only the three or four that I think come in them..

72, 80, 87, 95?

[wolf_walker]

Temps the same in ETKA, part numbers differ. 

[8v-of-fury]

I have seen no difference from 1.5 gas or diesel.. to my 1998 1.9 AHU even.

[wolf_walker]

Me neither, weird...

[vanbcguy]

The warmer the coolant is the less heat energy you are loosing to it from combustion.  There really is no point in running any cooler than the factory intended.  All the engine components and clearances are designed fro the factory temperature range, including +200°F operation, so I do not believe you are gaining anything running it cooler, other than a decrease in efficiency.

I have heard the argument about having headroom to prevent an overheat before - while there is some validity in this a better solution would be to make sure the cooling system is working properly.  Again VW tests all their cars in both high and low temperature extremes and they seemed to think it was ok.

[wolf_walker]

The warmer the coolant is the less heat energy you are loosing to it from combustion.  There really is no point in running any cooler than the factory intended.  All the engine components and clearances are designed fro the factory temperature range, including +200°F operation, so I do not believe you are gaining anything running it cooler, other than a decrease in efficiency.

I have heard the argument about having headroom to prevent an overheat before - while there is some validity in this a better solution would be to make sure the cooling system is working properly.  Again VW tests all their cars in both high and low temperature extremes and they seemed to think it was ok.

Agree, but I think 220 is higher than it needs to be, the stat opens at 215 so I can assume VW didn't want it much higher than that.
I also wouldn't be shocked if they set the fan cut-in so high because it can be a noisy drag on a small diesel, obviously they tolerate
going that high regularly, but that isn't saying it's ideal.  I'm reminded of Volvo in the 80's adding a resistor board to the temp gauge to make it
NOT fluctuate because, despite it being normal, people complained because it moved.  Who's to say that they didn't set the fan cut-in temp high to keep people
from complaining about it?  That sort of things happens.

I had a fellow that worked with metal professionally question weather the differing expansion rates of the aluminum head and steel block
would contribute to tiny amounts of head/block/gasket wear over time with wide operating temp swings.  I can't answer that one, but in my perfect world
the motor would be 200F and never change.  It's a goal.

[8v-of-fury]

I had a fellow that worked with metal professionally question weather the differing expansion rates of the aluminum head and steel block
would contribute to tiny amounts of head/block/gasket wear over time with wide operating temp swings. 

How much time? Like 30 years and 400k + miles? ;)