Overheating Honda - Heater will cool 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

 

I know... your thinking thermostat right? Well here is the catch.

I assume that by "The temperature goes down when you put it on full
blast" you mean turning the heat to max and turn the ventilation fan to
the highest speed. This does move heat away from the cooling system (and
dumps it in the cabin). It also indicates that you do have coolant
circulation (so the water pump must be working). I would say this is a
classic case of a failed thermostat. If you still have the original
thermostat in the car you would have received all the service you can
expect from it.

 

Agreed. I've had two thermostats go in two different cars (both Toyota
MR2's, incidentally), and the symptoms both times were exactly as described
here.

 

I agree with the intelligent people that told you the thermostat was the
problem. Talk to the mechanic before you have them install a new
thermostat.
In the future, don't replace the radiator unless it is leaking or totally
rusted out. In many cases, if the radiator is not rusted--you can have it
repaired at any radiator shop.