Overheating Problem - Heater cools down

I have a 92 Honda Civic. One day the temperature shot up to really
high on the gauge. I managed to get home etc. without damage to engine
after allowing to cool etc.

I inspected the next day and replaced the radiator and coolant. Took
it for a test run and worked well... but then shot up to the red
again.

I have recently had the water pump replaced and am sure the fan is
working properly.

I know... your thinking thermostat right? Well here is the catch.
The temperature goes down when you put it on full blast??? This makes
for uncomfortable driving during the summer months!

Could this be the thermostat or a blocked heater hose?

Any ideas would be appreciated.

Gerard

 

Possable head gasket leak.

 

Are you confusing thermostat for radiator with thermostat
for cabin heat? They are completely different systems that
share only one thing - coolant and engine heat.

Why, pray tell, would you just wildly replace things before
first discovering the failure? If radiator was reason for
failure, then some simple testing would have made that
obvious. Shop manual even provides a simple 'kitchen' test to
locate reason for failure. Suggest you get that so inexpensive
shop manual before fixing things. Even how to test a
thermostat can destroy the thermostat if basic and obvious
precautions are not exercised.

Most mechanics no longer perform such tests because (if they
are any good) they have already learned from such testing or
equivalent. But being so new to repair, learn some of what a
mechanic calls 'common sense'. A manual is more important to
you than it would be to a professional mechanic. IOW your
original question was already answered by those nine pages in
section 10 of that shop manual.