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1994 4.0l Heater issue


RonD

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Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Heat is not even luke warm after engine warms up

On the '94 there is no by-pass or heat control valve on heater hoses
Hoses run from upper intake and water pump directly to heater core hook ups on firewall, so core always has coolant flowing when engine is running

Both hoses get hot, not just warm but normal hot
Temp gauge running just below 1/2 as usual after warm up

Blend door is cable activated and is accessible by opening glove box door all the way.
When sliding lever from cold to hot it does change heat from no heat(cold) to just a little heat, and you can hear the "thump" when closed for full heat, and reaching in above glove box I can manually unhook cable and move blend door, all seems fine, can clearly hear it close.

Figured heater core partially block, but core is only 3 or 4 years old and when original core clogged engine temp gauge would go up above 1/2 then drop back to normal randomly because heater core is the water pumps by-pass on this model year.
But removed hoses and flushed core in both directions anyway, flow was great both ways.

If I turn off engine and let it sit for a minute or two then turn on heat/fan it comes out very hot.
But if I do the same with engine idling it doesn't come out as hot, a little hotter but nothing like when engine was off.

I am missing something obvious but can't for the life of me figure out what :)
 


RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,290
Reaction score
8,292
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Just a follow up as to what the problem was, getting colder up here so decided to get to the bottom of it


Heater core WAS PLUGGED UP, but flow thru it was still good.
Pulled out the core(to get to Blend Door) and flipped it upside down, small trickle came out but you could hear there was coolant still inside by shaking it.
So bottom passages were plugged up
 
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