Relationship between thermostat temp and fan swith temp

[wolf_walker]

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? ;)

That was my thought, hey stuff like that matters when you drive these things for most of a lifetime lol...

My 600K'er started showing the metal stretching around the strut towers after 500K, different things start to matter
after really long mileage. 

[nwcali6]

  In my experience with the thermostats in these is that they are often not very accurate.  My TDI was always low, replaced it (now stays at a even 190 when warm) and my 1.6 often runs too cold, even then I had to try two different ones to get it to stay where it does...

  I'm waiting for summer before I go with another one, thinking the hills around here and the fact that I'll be running it hard will keep it warmer...and I'll be inland a good bit. 

  I'd recommend keeping an eye on the temps when putting in a new one... I also had one not open until 230 or so...

  Maybe I need to get a German made one?

[wolf_walker]

I'd never use other than behr or wahler.

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[Smokey Eddy]

There is no relationship between the two. The fan switch will only switch when the outflow of the rad exceeds some specification (like 92C - that sounds about right).
The temp of the t-stat, so long as its less than 92C, won't change this fact in any way.

[damac]

I have been watching my gages on 79 rabbit this last week.

With temp gage in the head out port

With a stock tstat/radiator fan switch it shows mostly steady 190 when up to temp and driving around normally.  Mine can idle a long ass time before a fan cycle hits.

But I noticed for example on a longer stretch of hill where I am making the car pull and boost going 70+ mph that the egts rise to 1000+ and the temp will slowly clime to about 210 before the fan starts blowing and brings the temps down.

[8v-of-fury]

Going 70+ mph should already be flowing more air through the radiator than the fan could pull through on its own.

I can spike my coolant to 220-230F on a long hill climb. Dunno what the EGT's are, afraid to know! lol

[wolf_walker]

The two foot long 4"x4" oil cooler fixed a lot of that crap on my 82 when it was still turbo'd VS the factory water/oil deal the factory put on there.
Even NA I can run up many mile long steepish inclines in 5th with it on the floor at high elevations and never really see much in the way of high temps.
It's imperfect and a little inconvenient (and overkill) but it works, especially when there is airflow. 

[8v-of-fury]

4"x4" is hardly overkill? haha that is fairly small no?

I wish to do a good oil cooler setup, the AWIC, as well as a few more gauges and temp sensors around the engine on my next set of "upgrades".

[wolf_walker]

http://imageshack.us/a/img689/9039/20130317161917.jpg

http://imageshack.us/a/img255/9263/20130317161910.jpg

It's a little hefty. It was cheap though..

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[nwcali6]

There is no relationship between the two. The fan switch will only switch when the outflow of the rad exceeds some specification (like 92C - that sounds about right).
The temp of the t-stat, so long as its less than 92C, won't change this fact in any way.

  The relationship being that if the thermostat doesn't open until late then the fan might be set lower... My TDI is stock (don't know why I'd change it) and my 1.6 has a 94 VW gas radiator mounted up front (in a jeep) and doesn't even come close to hot unless I'm wheeling).  I'm not sure why anyone would change stock..

  I'm going to try the brands someone else mentioned on here for the T stat.  Murray doesn't seem to cut it (but one in it now is OEM/german)

[bbob203]

I'm going to replace both my thermoststat and switch together so they match because I'm not sure if they do. on a 4th gear hill climb at 45 my coolant temp will go up above half 10-11 psi of boost just under wot. I have no egt guage and my fuels turned up a bit. what temp on the thermo and switch would you guys recommend?

[8v-of-fury]

Just above half is totally safe (assuming your gauge is accurate) as the fan doesn't even come on to just above 3/4.

[wolf_walker]

I cut my automotive teeth on old domestic v8 stuff, where with a mechanical gauge, the temp went to 180 or 190, and stayed there.
There was significantly more reserve capacity I guess one would call it when the radiator was the size of the hood on my VW, and
the gradual cut-in of a mechanical clutch fan likely helped.
I observed this behavior with W123/126 Mercedes as well.

Ever sense, a temp gauge that moves around after warm-up has never sat well with me.  It isn't wrong or even particularly undesirable maybe,
but it isn't my preference.

If I ever get around to actually building one of these guys from scratch I plan to try out that waterless coolant, Evans or whoever it is now.
I wonder if the later two stage cooling fans wasn't an effort by VW (and others) to more pleasantly regulate the temp spikes when not in
motion too.