|Thermostats - new and used
We get all kinds of questions about thermostats and
flaps... maybe you are wondering:
What are thermostat flaps anyway?
The thermostat flaps fit up inside the fan shroud on either side and are connected by a linkage to
each other and down to the thermostat which is located between the #1 & #2 cylinders. The flaps
are nearly (but not completely) closed when the engine is cold. When you start the engine,
heated air from around these cylinders causes the thermostat to expand once the air reaches the
opening temperature. This causes the linkage to move and the flaps to open. As the engine temp
rises, the air over the cylinders gets hotter, causing the thermostat to expand more. This is self
regulating, meaning that when the engine heats up, the flaps expand, and when the engine cools
down, the flaps close.
It does not get cold where I live, or I only drive in the summer, do I really need to run thermostat
The point of the thermostat flaps is not to provide cooling. The flaps are there to get the
engine heated up to proper operating temperature as fast as possible and then
maintain that temperature. This is the #1 mis-conception about the thermostat and flaps
system. Everyone thinks they are meant to keep the engine cool, when it really is meant to heat it
up quickly. But NO, you are not required to run the thermostat flaps. Many air cooled VW's are
running all over the world, in all sorts of temperatures and conditions with the flaps missing.
However, all of those engines are running too cold at startup. This means that all of those
engines have lower fuel economy (less MPG), more engine wear, and resulting shorter engine
life. So, if you are not concerned about those things, you don't need thermostat flaps.
Can the flaps get stuck closed, causing the engine to overheat?
Nothing is impossible, so yes, they could get rusted closed or hung up in the closed position,
which would result in an overheated engine. However, I have rebuilt 100's of thermostat flaps and
only seen 3 that where rusted shut. With a fresh blasting and powdercoat, you should be fine for
many years to come.
Can the thermostat get stuck closed, causing the engine to overheat?
The German thermostats are fail safe, meaning that if they fail, they SHOULD fail in the full open
position, giving you maximum cooling. I have seen 100's of thermostats over the years, and I
have only seen a 3 that where contracted that did not expand when heated. So it is possible, but
it is not very likely.
The VW Mexico version of the thermostat is NOT fail safe, meaning that if the wax inside leaks
out, it will stay fully closed. However, I have never actually seen a failed thermostat of this style,
nor have I heard of any of them failing, so it must not be very common.
How does the thermostat work anyway?
The German units have a small amount of liquid inside that expands when heated. The bellows
are held closed by the partial vacuum inside the sealed unit. As the stat is heated, the liquid
vaporizes and the bellows expands. When the stat cools off, the vapor returns to liquid and the
bellows contracts. If the liquid ever leaks out, the bellows will expand, causing the flaps to go full
open. This is why the German stat is considered fail safe.
The Mexican units have a small amount of wax inside that expands when heated. The unit is held
closed due to a large high tension spring. As the stat heats up, the wax expands, extending the
stat. When the stat cools off, the was is compressed by the high tension spring. If the wax ever
leaks out, the stat will stay in the closed position. This is why the Mexican stat is NOT considered
fail safe. I guess you would call that fail unsafe.
Why do you offer 3 different types of thermostats?
It depends on what the customer wants and his/her budget. The rebuilt units are the only ones
that come with a warranty. Also, if you are running an after market "tucked up" exhaust, such as
the A1 Sidewinder, the German stat will hit it, so you have to run the Mexican one.
What temperature does the thermostat open at?
It depends on which thermostat you have:
German stat for type I carb engine, starts to open at 65-70C (149-158F)
German stat for type I FI engine, starts to open at 80-85C (176-185F)
German stat for type IV carb and FI engines, and 4 cylinder Porsche 912 and 914 engines, starts
to open at 85-90C (185-194F)
German stat for Porsche 356, these engines do not have flaps, the stat opens ductwork to run
heated air to the carb intakes (23-34C)
new VW Mexico - this is a real mess, as it comes in both the 65-70C range and the 80-85C
range, yet somehow has the same part number? So, what do you got? The only way to know is to
My engine oil temperature is X, so should the flaps be open now?
Both the engine oil temperature and the temperature of the air coming off the cylinders are due
to the heat generated by the engine running. But there is not a direct connection. Don't try and
use 1 to determine the other.
I drove the car for 5 minutes and the flaps are not open yet. What is wrong?
The flaps are still closed because the engine has not heated up yet. The minimum temperature
the thermostat has to see is 65C (149F) - it just has not gotten that hot yet.
Do I have to run all the lower cylinder tins (heater box sled, #2/#4 air deflectors, industrial shields)
or can I leave all that off?
You MUST run all of the lower engine tin when you are running a thermostat. If you do not, then
cooler air from below the car will mix with the heated air from you engine. This will result in the stat
not opening the right amount, or even keep it from opening at all. This is super important! If
you are not running heater boxes, then you need to run the industrial shields to fill in this open
I have a VW type IV or Porsche 912 or 914 engine, can I run a bug thermostat on it? They look
They look the same, but the type IV opens at a higher temperature.
Can I run a Corvair thermostat on my bug engine? They look the similar.
The Corvair stat opens at 85-90C, which is too hot for a bug engine, but would work for the type
IV, Porsche 912 and 914 engines. But the fittings on both ends are wrong. You would have to
make some sort of adapter.
Will a bug thermostat work on a Porsche 356?
No, the Porsche 356 thermostat is a much lower temperature. There are no flaps on the 356
engine. This stat opens ductwork for warm air to go to the carburator intakes. A totally different
|100% Brand new, USA made,
GERMAN style thermostat - with a
2 year warranty - $119
65-70C for carb opening range or
80-85C for FI opening range
|GOOD TESTED USED GERMAN
THERMOSTAT - $65, but can change
based on supply
Each unit is tested, and it might work or
years,,, or might fail next week. There is no
way to tell. They are at least 30 years old.
|NEW VW MEXICO
THERMOSTAT - $60
This stat requires a modified
It also uses a 12mm wrench to install
instead of a more typical 13mm.
Copyright 2009- 2012 Awesome Powdercoat LLC
|100% new, USA made,
GERMAN style type IV,
Porsche 912 / 914 thermostat
- with a 2 year warranty - $129
86-90C opening range
Add a brand new cable for
$10 if needed.
|100% new, USA
made, GERMAN style
thermostat - with a 2
year warranty - $139
23-34C opening range
|Each thermostat is
stamped on the
bottom with the temp
range, USA, and the
|Parts needed to make