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Heater not blowing heat

Tiny
AZMADMAN
  • MEMBER
  • 1989 CHEVROLET TRUCK
I've changed out my heater core and thermostat in the truck, fan blows high but no heat, checked hoses coming from core both are still cold, their is no valve, one of my hoses comes from heater core to engine the other from the heater core to the radiator, i've looked on the water pump to see if there could be a connection for that hose but their is not, any help would be appreciated, I would like to get my heater working. Its a 1989 k1500, with a 1995 5.7L engine in it, with a digital heater/ac unit, i've even checked the actuator and the blend door-they are operating, changed out the thermostat and the heater core, I have one heater core hose coming off the right side of the heater core going to the engine and the left hose going to the radiator, both hoses are cold to the feel with the engine running and the heater on high, i've filled the coolant level up, but don't get any heat with the controls on high. Ive also checked for a valve in the dash and in the engine compartment and I do not find one. I would like to get the heater working.
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Sunday, December 27th, 2009 AT 5:36 PM

37 Replies

Tiny
IMPALASS
  • MECHANIC
  • 3,112 POSTS
Hello

Is the vehicle reaching normal operating temperature on the dash gauge?

You do have plenty of coolant ..(just asking so we are on the same page) Why did you change the core? Most likely based on what you are saying there is either air in the system or your water pump is not circulating very well, but that would also affect the temp of the vehicle. I have also seen where the fitting on the engine going to the heater hose plug up I would remove the hose then start the engine for a seconds to see if coolant shoots out.

Here is a guide that can help

https://www.2carpros.com/articles/car-heater-not-working

Try disconnecting the return heater hose slightly to release any air in the core. Some have had to back flush the core to get the air out

Please let me know about the operating temp of the vehicle.
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Sunday, December 27th, 2009 AT 7:50 PM
Tiny
AZMADMAN
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  • 5 POSTS
OK, well I changed the core out because I didnt think it was working, thats what I originally thought the problem was since its an older vehicle, i've back flushed the heater core. I bought new thermostats but the vehicle overheated with the 195f stats in it, so I put the older one its a 180f thermostat and the truck doesnt overheat, but im not sure if its actually reaching proper temp with this thermostat in.
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Sunday, December 27th, 2009 AT 8:01 PM
Tiny
IMPALASS
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Hello -

Thanks for the info

Well, that doesn't mean it wasn't bad..... You are correct on older vehicles that is usually the problem. One way to check is to feel both heater hoses... If one is hot and the other not then no coolant through the core..... Thus core plugged.

If there was no heat at all and the temp gauge was reading really low, then possibly a thermostat stuck open.

How many miles on the vehicle?

It may be the water pump or the radiator..... If there is not good circulation through the radiator then that can cause the overheat too.

Now, I still think you have air in the system if the vehicle is reaching operating temp...
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Sunday, December 27th, 2009 AT 8:16 PM
Tiny
AZMADMAN
  • MEMBER
  • 5 POSTS
Milage is like 195000, I flushed out the radiator, temp on guage only comes up slightly-not much movement on temperature guage. Even when driving it. I've opened radiator cap with heat on high and topped off, doesnt seem to be air in system.
Brand new heater core, only overheats with new thermostat in, which is a 195f thermostat, thats why I put the old one back in -its a 180f thermostat and it doesnt seem to overheat with it in.
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Sunday, December 27th, 2009 AT 8:30 PM
Tiny
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Hello -

Did you try opening the return heater hose from the core to see if any coolant was coming out? Again, if your temp is coming up..... Then the heater hoses should feel the same as the upper and lower radiator hoses.

Also, I have had several gain in temperature and I had to keep shutting off, bleeding a little, adding a little, sitting the vehicle on a slope etc then finally the temp stabilized and then finally got good heat to the core.
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Sunday, December 27th, 2009 AT 8:48 PM
Tiny
AZMADMAN
  • MEMBER
  • 5 POSTS
How do I check my water pump to make sure its working properly?
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Sunday, December 27th, 2009 AT 9:09 PM
Tiny
IMPALASS
  • MECHANIC
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Hello -

Below is what you can check.

Park your car overnight and make sure the pavement underneath is dry. In the morning if the pavement is wet with liquid, you could have a water pump leak.

Grab opposite ends of the water pump pulley and check for "play" (looseness): Try to rock it back and forth. There should be no give. If there is, the bearings are going and it's time to replace the water pump. By the time you can feel play in the water pump pulley, you may also be able to hear the bad bearing when the engine is running - there may be a low-pitched grinding noise coming from the water pump pulley.

Visually check the water pump behind the pulley for signs of a coolant leak. If the water pump gasket is leaking, it must be replaced.

Also vehicles can overheat and or not cool properly.........

Now at that.....I don't see that is your problem..... The engine temp is okay..... It is the heater which leads me back to air in the system.

Have you found anything since our last chat?
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Monday, December 28th, 2009 AT 10:58 PM
Tiny
AZMADMAN
  • MEMBER
  • 5 POSTS
Well I had one of the heater hoses in the wrong place, I had it on the radiator and it was suppose to hook up to the water pump, the water pump had a fitting plug in the top of it and had to be replaced with a hose fitting which I did, but after connecting the hose back up and filling the system with coolant, I checked for air in the system, after filling system more and loosening hoses to expel air, I still do not get hot air from the heater, im beginning to think it is the water pump because both heater core hoses are still cold and I just put in a brand new heater core.
The vehicle will not overheat with a 180f thermostat in it, but did seem to before with a 195f thermostat, Do you think it could be the water pump, there's no play in the pulleys and no grinding of berrings?
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Tuesday, December 29th, 2009 AT 3:51 PM
Tiny
IMPALASS
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Hello -

I have seen the propeller shaft so worn it was not circulating water very well but it went with overheating.

When you disconnect the hose at the heater core did you get good water flow or just kind of trickled out?

It may be the water pump but I am not totally sold on that. I am going to ask another moderator to assist to see what they think also.
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Tuesday, December 29th, 2009 AT 9:12 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
One way to test for a bad water pump is to squeeze the upper radiator hose when the engine is hot and idling. Careful, because the hose will be HOT! If you do not feel much coolant circulating through the hose when you rev the engine, the pump may be bad. The other cause might be a bad thermostat that is not opening properly (remove and inspect the thermostat), or a clogged radiator.
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Wednesday, December 30th, 2009 AT 2:16 AM
Tiny
88 SILVERADO
  • MEMBER
  • 1 POST
Hello, I have a 88 silverado that had the same problem! I replaced everything, and when I went to replace the fan and clutch, I found out there were some motors back in 88 and 89 that were counter-rotating motors. After replacing the fan and clutch, I had to also put a waterpump on that is for a counter rotating motor in order to get enough water thru my heater core to actually get some heat! Sounds crazy, but go to Napa and ask if there are counter rotating 5.7 motors in some of the 88 and 89 pickups. Solved my overheating problems and no heat problems when I found out everything was running backwards.
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Sunday, January 29th, 2017 AT 4:20 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,490 POSTS
Hey 88 SILVERADO,

Great addition to the thread nice work, please use 2Carpros anytime.

Best, Ken
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Thursday, February 2nd, 2017 AT 5:15 AM
Tiny
DRUMMERGATOR
  • MEMBER
  • 1 POST
  • 1989 CHEVROLET TRUCK
THE HEAT OUTPUT WAS FINE TILL FRIDAY. I REPLACED THE THERMOSTAT & GASKET, STILL NO HEAT. MY CHILTONS MANUAL SAYS TO INSTALL THE NEW STAT WITH THE SPRING FACING TOWARDS THE UPPER RADIATOR HOSE FLANGE. ANY TRUTH IN THIS? THANKS !
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Wednesday, November 22nd, 2017 AT 6:51 PM (Merged)
Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
Yes there is truth in it.

Would like you to buy some radiator and coolant system flush and flush out the whole system.

Next bleed the system and the heat should be as good as new.
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Wednesday, November 22nd, 2017 AT 6:51 PM (Merged)
Tiny
JERRODHELTON
  • MEMBER
  • 1 POST
  • 1989 CHEVROLET TRUCK
  • 185 MILES
I have an 1989 k1500 having heater problems temp guage goes to about 240 then back down when it goes down I have luke warm air as long as I acclerate if I let off acclerater it get cold again
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Wednesday, November 22nd, 2017 AT 6:51 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Make sure the coolant level is full. Check to make sure the thermostat is working properly.
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Wednesday, November 22nd, 2017 AT 6:51 PM (Merged)
Tiny
JOHN21757
  • MEMBER
  • 1 POST
  • 1987 CHEVROLET TRUCK
  • V8
  • 4WD
  • AUTOMATIC
  • 116,071 MILES
Heater problem
1987 Chevy Truck V8 Four Wheel Drive Automatic 116071 miles

I have a 87 chevy scottsdale all original. Just bought last week, very well maintained. The heater blows cold air. Replaced thermostat with oem 195 (had 180 in it) and filled all coolant levels. Temp gauge varies between 190 and 210 while running. One heater hose is warm, the other is cold. Mechanic today said the heater hose that goes into the intake manifold has a heater control valve that he suspects is bad, therefore not allowing coolant to circulate and get hot. I also notice with the Radiator cap off, my water level in the radiator goes up and spills out and then way down, instead of continually circulating. Ant thoughts?
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Wednesday, November 22nd, 2017 AT 6:51 PM (Merged)
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Check for the heat control valve as instructed, operate it by hand if you can and see if the other hose warms up, if not the heater core needs flushing or replacement. You may still have a bad tstat.I also have seen waterpumps with impellers so disolved, the circulating power is gone!
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Wednesday, November 22nd, 2017 AT 6:51 PM (Merged)
Tiny
DOUG HOPLAND
  • MEMBER
  • 1 POST
  • 1988 CHEVROLET TRUCK
  • 7.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
My truck is a 3500, with air conditioning. It has the digital dash.
Sometimes I turn truck on first thing and have heat controls set to warm temp and floor heat. The display shows what I want.
As engine gets to normal temperature on gauge. Sometimes I get heat, sometimes no heat. I have turned dash control off and back on and still no heat. Sometimes I turn engine off, and restart, and then I have heat.
I cannot get display new anymore as it is not made.
I put used dash control in, made no difference. When I shut engine off after my trip I always make sure dash display is on high heat.
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Wednesday, November 22nd, 2017 AT 6:51 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,490 POSTS
Hello,

The first thing that comes to mind is the temperature control actuator has gone out. Here is a complete guide on which one it is and how to replace it, here is also a guide on checking the heater out.

https://www.2carpros.com/articles/replace-blend-door-motor

and

https://www.2carpros.com/articles/car-heater-not-working

Please let us know what you find ;)

Cheers, Ken

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Wednesday, November 22nd, 2017 AT 6:51 PM (Merged)

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