Al Gietzen wrote:

Just this week I had a thermostat fail closed in my Dodge van.  Tightly
closed - absolutely sealed (there is no air bleed hole).  What was
surprising is that it didn't happen at start up.  I had driven about 5
miles; made a brief stop; driven another 5 miles at freeway speeds; another
brief stop; then about 5 more miles up and down some long hills.  Then
suddenly heard the boiling and had steam coming up from the engine.

Admittedly, I had not looked at the temp guage along the way; but doubt that
I could have gone that far before boil-over if the thermostat were stuck
from startup.  So I now doubt arguements that if a therostat fails closed
(and they do), you would know it before takeoff.

I have also experienced failed-open thermostats twice in 9 years on my
Jaguar (it has two).  I doubt that Mazda thermostats are exempt from
failures.

I have hesitated on the decision of putting a thermosat in the 20B in my
Velocity.  Since I have two cooling radiators in parallel, I am considering
a thermostat in one of the loops instead of the engine.  Although without
variable air flow, I'd guess warmup would still be pretty slow on a cold
day; and may run cool during descent.

During climb and probably in cruise [???] you are going to have to have
the cowl flaps open, thus draggy when you don't want it.

Cooling requirements are highest during climbout.  Cruise power is lower,
and air temperatures at altitude are (generally) lower.  Generally flaps
would be closed (or mostly closed) at cruise.

Al Gietzen

 
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