XR4Ti Archived Tech Articles

    How To Get Heat From Your XR - A write-up on the tests, trials and tribulations I made while working on the heating system of my XR4Ti.

Post Date:    Wed, 15 Oct 1997
Subject:      Heating system shortfall - XR4 - it's that time again...
List:         IMON

I was enjoying my lackluster heating system on the way home from work this
morning (I work 3rd) and decided that I was fed up with the inconsistencies
of it's peformance and felt like I had had just about enough.

Quick history and summary:
- 87 XR4, 5-speed
- new 180' thermostat as of 6/96 (why I chose the 180, I'll never know)
- new heater core as of the coldest day in January 97 (can you say
- new heater control valve as of the day after the heater core went in
- SVO roller camshaft (.420/.420  274/282 set @ 4' advanced)

- excellent heat at highway speeds (rpm more important) for a 180' thermostat
- any time the rpm drops into or below 2000 heat all but goes away

Recent work done:
- coolant level checked and filled last Saturday
- major (MAJOR) vacuum leak fixed last Saturday
- sprayed most of the vacuum lines and fittings with ether based starting
  fluid to check for other vacuum leaks (anyone know of a more accurate

Tests done and results:
- vacuum draw checked by my MITY-VAC vacuum (gauge (on hand pump), 18~19
  inches, it used to jump from 11~15 before the leak was fixed on Saturday
- heater temp output checked this morning at center vent, controls set to
  full hot, full dash, center vent is the only one open
- temp checked with Radio Shack digital Car/RV thermometer cat #63-1019,
  probe was IN the vent about 1 inch

Here's the hard numbers:
ambient: 37'F
idle output temp: 48~52'F
at 2000 rpm: 49~55'F
at 3000 rpm: 119~123'F
peak temp recorded: 125.4'F
under these conditions: spirited acceleration through 4 gears, max rpm - 5300

So, I have replaced quite a bit of the componentry.  Cooling system works
well, and thermostat is not stuck open (from 'hand on upper hose til it
suddenly gets warm' test).  I can't seem to find any vacuum leaks.  Is my
camshaft or it's advance setting just not allowing enough vacuum to do the
job?  I'd think advancing the cam would make more low-end vacuum.  Is there a
problem with the air door or it's overly complex operating system (resevior,
soleniod, air door vacuum motor, etc.).  If I put my MITY-VAC on the heater
control valve and pumped it up (or down rather, since se are talking about
vacuum) should I notice a change in the heat?  Dumb question, I must be
getting to tired to go back out there.

What about the vacuum line routing for the air door?  The way mine is plumbed
there might have been some changes in it's previous life.  The routing is
this: line into resevior from engine, line out of resevior to a Tee, one
branch of Tee goes to the solenoid, the other branch disappears behind the
sheilding - must go to the door.

This can't be correct, there is no Ford part number on that small little
vacuum Tee (only kidding).  So, what does everybody think?


Post Date:    Fri, 17 Oct 1997
Subject:      Heating system shortfall - update
List:         IMON

Here is the update.  From what I have gotten from the list here are the
changes with the heat, changes made, and the changes going to be made:

In my previous letter I described that the heat came at somewhere just over
2000 rpm.  I was guessing that this was vacuum related due to my camshaft
choice, or a large, hidden vacuum leak.  Well, now the heat isn't there at
3000+ rpm...   Hmmm.  I never got to check out the heat over 3000, I ended up
at home.

Here are the fixes suggested:
Lack of vacuum present at the heater contol valve (one vote).
Remove heater control valve all together (a few votes).
Water pump impeller corroded away (most votes for this one).

When It comes to the water pump, I probably do need to replace it (more
later).  But this change in the range that heat is now available has led me
to look in other areas.

My air door doesn't work...  It must be a bad solenoid.  This is coming from
Rapido's latest newsletter.  I am going to hardwire the air door vacuum line
right to resevior.  Maybe that'll close it.  Then I can get some *clean* air
into the car.  Next I will be checking for vacuum present at the heater
control valve when the heat is on and when the heat is off.

If nothing else seems to work, then I guess I'll tear into the water pump.
 Here is what I was going to reveal later.  Last winter, when hell was
freezing over, my cooling system froze solid.  Boy, that was a day.  I have
since been very careful to watch my coolant/water ratios.  I am thinking that
even though my cooling system problem has changed faster than an impeller can
rust off, I will replace my pump anyway...  Oh, one more thing, I will swap
out the 180' thermostat too...

I'll keep eveyone post about what happens.  Which leads me to one final
thing.  Thanks to everyone who took the time to respond to my post.  I meant
to mail you back, but may have overlooekd you.  Thanks again!


Post Date:    Wed, 22 Oct 1997
Subject:      Heating System Update - Strange Behavior, XR4
List:         IMON

Here's the word on my heating system.  It stinks.

My first post on this (Heating System Shortfall) had some test results from
my 87 XR4.  Here is a quick review (from memory):

- ambient 45' F (or so)
heat output (based on my Radio Shack digital car thermometer cat # 63-1019):
- 1000~2000 rpm = 49-54' F
- 2000~2500 rpm = 90' F (or so)
- 3000+ rpm = 119-123'F
- peak temp 124.2'F (I think)

The car is equipped with the SVO cam (.420/.420 274/282) advanced 4'.  I had
just fixed a major vacuum leak at the resevior and added coolant.  The
thermostat is a 180' unit.  Soon to be replaced...

Well, since then.  Driving at 35 the temp gauge rockets up to the halfway
point (no purple ring, so the car must be overheating...).  I pull the car
over - no boiling coolant, no smoke, no glowing exhaust system.  Just the
sound of the coolant DRAINING from the tank.  Hmmmm...  An air bubble musta
passed the temp sender.  I proceeded to put ONE GALLON of 50/50 coolant.
 WOW!!!  I thought I filled it up...  Well, needless to say, I hadn't.  I was
thinking "WOW, now I'll have heat..."

Sure, I got a little more.  Not much.  No tests run.

Next day I ran the tests to determine whether or not the air door was
closing.  No thump.  I plumbed the air door vacuum line right to the
resevior.  Now it closes.  The air is no longer entering the car - well, not
as much as before...  So, time for more tests.

This morning:
ambient - 34'F
-  idle = 64' F
-  1500 rpm = 110' F (wow, I never got this much heat so low...)
-  2000 rpm = 136' F average
-  3000 rpm = 142' F average
-  4000 rpm = engine disliking the driver a lot, 142' F still
-  peak temp = 145.5' F

So, I guess I have heat.  All of these tests wer run with the heat set to
max, the vlower set at III, the output set at panel, and all vents closed
expect the left center where the temp was taken.

There's more.  This is the strange behavior part.  I decided to add as much
vacuum at the Heater Control Valve (HCV) as my MITY-VAC could muster.  So, I
parked the car and applied 27 in. Hg. to the HCV (with the vacuum line
plugged).  The heat output (wiith the same setup as before) dropped into the
75~80' range.  HUH?  Okay, maybe I am over-extending the HCV movement.  So I
dropped the vacuum to 17.5 in. Hg.  (average level of vacuum @ idle from my
engine comination).  The temp didn't budge.  Okay, maybe I have the concept
backwards of how the HCV operates.  I applied 0 in.Hg. (disconnected the

Oh, I did bring the rpm up to 2K at some point during the test (17.5 in.Hg.).
 Nothing changed.

I couldn't find anything suitable for use as a Tee to check how much vacuum
is available at the HCV.


Update: April 2001

After struggling for a few more weeks with the heater, I finally assembled 
an adequate series of repairs to increase heat output.  Replace the heater 
core first, then, if there cold air blowing into the car, plumb the air door
solenoid right into the vacuum reservior.  Finally, make sure you don't have
a thermostat that is not the stock 195 unit.  The 180 thermostat is a
waste of time.

That's it!  I've done this to two XRs and I always get good heat.

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Published by Chris Anglin.