84 spider heater (intermittent)

[Rodney Tidwell <rodneygt@xxxxxxxxxxx>]

Hi all,

I bought my spider in April.  Last weekend was the first time I've had
an opportunity to use the heater.  I was driving at night.  It was
chilly with the top down.  I turned the heater on.  It seemed to work
okay, for awhile.  I stopped at a convenience store.  I left.  A few
miles down the road, the heater seemed not to be working to well.  By
the time I reached my destination, there was no heat (a 40 mile trip).
I'm referring, of course, to hot air from the heater core, not the
blower motor.
Last night the heat worked for a 10 mile trip.
This morning the heat worked but not this evening.
Even when the heat was working during the last few days, it never was
really hot - just warm, though sufficient for my climate in winter.

There does not seem to be any pressure on the heater hose to the core or
on the return hose to the water pump. If I squeeze the large hose to the
top of the radiator, I can feel pressure between the firewall and the
bleed valve on the throttle housing, so I don't feel there is a clog at
the thermostat outlet or the bleed valve.

I assume my problem is one of the following:
1)Heater core and/or heater valve is mostly clogged (my #1 choice)
2)Heater valve is broken (seems unlikely since heat works sometimes)
3)Something is affecting the linkage between the heat lever and the
valve (also seems unlikely)
or,
What about air in the system?

I plan to flush (the stuff in the little prestone bottle) the entire
cooling system this weekend.  I also thought about forcing some of the
"flush" chemical through the heater core by way of  the hose between the
firewall and the air bleed valve with the aid of compressed air, if
necessary.  If the latter is advisable, what is the max psi I should set
my compressor regulator at?

Any advice appreciated.

Thanks,

Rodney
McComb, MS

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