1995 Mazda MPV NO HEAT

Tiny
JEFFREY10X2
  • MEMBER
  • 1995 MAZDA MPV
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 130,000 MILES
I have a 1995 mazda MPV. The heater blows warm air only, if you drive it, it gets cool. I have replaced the thermostat, flushed the heater cores, flushed the engine, and even went to the extent of bypassing the rear heatercore. Still no change. Kinda stumped here. Please help
Thursday, January 3rd, 2008 AT 5:23 PM

12 Replies

Tiny
BLACKOP555
  • MECHANIC
  • 10,386 POSTS
Hows your temperature guage is it saying normal operating temperature.

When the heat starts to get cold, stop immediateley and feel the heater core hoses, let me know what you find. If they are both hot, one, or neither.
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Thursday, January 3rd, 2008 AT 7:20 PM
Tiny
JEFFREY10X2
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Temp gauge is normal, I tried to check the hoses also,
they are both warm, almost like there is not enough flow through it. I even put a fluching T in the back at the inlet hose of the heatercore and I can take the cap off and the waterpump doesnt force anything out unless I put my filling funnel on the rad and put the level higher than the flushing T cap.
I was thinking it may be the waterpump. I have been turning wrenches for 24 years and have had one car( a mitsu.) That had no heat, but it would overheat, ended up being the fins on the impeller was rotted off.
But I dont lose coolant on the mazda and it doesnt overheat at all.
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Thursday, January 3rd, 2008 AT 9:16 PM
Tiny
BLACKOP555
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May be a bad temperature valve, follow the lines from the heater core back from the engine, you should find it before it gets back to the engine, it will be tied in with the heater core llnes. If that is good then you may need to check your blend doors under the dash. If the water pump was bad, it would be over heating more then likely.
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Thursday, January 3rd, 2008 AT 9:26 PM
Tiny
JEFFREY10X2
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Where would the heater valve be located?
The return hose goes into the thermostat housing,
the other looks like it goes to the waterpump housing.
I didnt see a vavle in the system.
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Thursday, January 3rd, 2008 AT 9:29 PM
Tiny
BLACKOP555
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In that case you may not have one. You may want to go with a higher temp thermostat.
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Thursday, January 3rd, 2008 AT 9:45 PM
Tiny
JEFFREY10X2
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  • 6 POSTS
I was going to when I replaced it, they make one thermostat for the car, and its a 180. No other options.

If I do squeeze the inlet hose repeatedly, I can get heat out of it, but then when I stop, it stops too.
It just seems like it isnt flowing, but when I put water with a hose into the inlet hose to back flush the system, it flowed great out of the heatercore.

Im stumped.
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Thursday, January 3rd, 2008 AT 9:48 PM
Tiny
BLACKOP555
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$* & I forgot to mention that you shoudl try to bleed your cooling system of air, this could cause this problem!
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Thursday, January 3rd, 2008 AT 9:51 PM
Tiny
JEFFREY10X2
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Done that too, thats why I installed a flushing T in the heatercore. I tried that with the car inclinded in the front, in the rear and still no change
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Thursday, January 3rd, 2008 AT 9:54 PM
Tiny
BLACKOP555
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I am stumped as well, the only thing else that can be checked is your water pump, but as I said it would probably overheat or run hotter then normal if it was bad. Ill do some reasearch and ask around and ill post back if I find out whats wrong, sorry I cant be of more help.
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Thursday, January 3rd, 2008 AT 9:59 PM
Tiny
BLACKOP555
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This reminds me of this other fellows post

https://www.2carpros.com/forum/engine-is-warm-but-no-heat-in-the-cab.-vt66389.html

try what he did, take each individual hose and flush it, sometimes flushing the system if a hose is to plugged it will find its way around it.
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Thursday, January 3rd, 2008 AT 10:03 PM
Tiny
JEFFREY10X2
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He said he had 125 degrees out of the defroster, that doesnt seem high enough.
I check all temps at low blower and when I first bypassed the rear heater, it was 165 out of the center vent. Then it was gone when I drove it.
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Thursday, January 3rd, 2008 AT 10:12 PM
Tiny
BLACKOP555
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Thats what gets me, what would cause it to go cold when driving it.
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Friday, January 4th, 2008 AT 7:16 AM

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