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coolant light - no heat

To: "" <>
Subject: coolant light - no heat
From: Dave Massey <>
Date: Sat, 11 Jan 2003 18:37:31 -0500
Cc: "[unknown]" <>, "[unknown]" <> id h0BNg1RO011517
Message text written by
>the coolant light on my 1980 tr7 sometimes stays on for the first 60
that the car is running.  the heat sometimes does not blow hot, but rather
cool like the heater core is blocked.  i have checked the coolant level and
it is fine.  i swapped the heater core hoses around in case the heater core
was clogged.  the water temp guage reads the same exact spot, up about 25%
and behaves perfect.  the car seems to reach and stay at the same temp.
what would cause the idiot like to stay on for the first 60 seconds ?  what
else could cause the heat not to go hot occassionally ?  thanks.  larry,

The coolant light responds to a probe in the coolant header tank.  It is
possible that the coolant level is borderline and it takes 60 seconds for
the coolant level there to reach a level that will turn it off.  However,
it is more likely that the control module is not functioning properly. 
These things tend to get tempermental.  I had to replace the IC in there
with a CD4093 to get mine to work.  It would turn the light on and then off
at random for no appearent reason before I fixed it.

As far has heater operation goes, there could be any number of things
causing it to not heat.  When the engine is fully warm check the two hoses.
 Is one significantly colder than the other?  If so then there is
inadequate coolant flow through the core.  It could be the valve not
working (pain in the *&%) or a clogged core (bigger pain in the *&%) or
something clogging the hoses or the ports where they connect (much easier
to access) or the linkage to the valve. 

A few months back a lister found that the DPO stuck something in one of the
hoses to block off flow.

In my case I found that my core had been frozen once and the tank had
swollen out.  Since both hose connections are on the same end of the core
there is a separator between the inlet and the outlet but with a swollen
tank there wasn't enough separator and the coolant bypassed the core
altogether.  (Of course this meant pulling the dash and the heater unit to
fix so let's hope this isn't your problem)

Good luck


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