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Discussion Starter #1
My '86 4Runner doesn't produce much, if any heat. The rear heater produces good heat.

Here's what I've done/checked...

- flushed heater core on two separate occasions both forward and backwards.
- replaced a working t-stat for a new OEM t-stat
- felt hoses going into core and they're hot
- checked and adjusted wire going to the heater control valve
- confirmed that the under dash wire was closing/opening the temp. control flap properly
- pulled the heater control valve and flushed/cleaned it and made sure it was working. Seems good.
- burped the cooling system and topped it up
- blower motors are working great.
- rad is new and flows well

Any hints on what else it could be? I'm at wits end here and will take ANY tips or hints. Would a bad heater core still flow water well when flushed?

Thanks in advance!

Warren
 

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the hot water going TO the core should be hot-- the return line FROM the core should be warm-
if you have hot water thru the valve- the 'blend' door in the case has to be the problem- with one exception---------------------
Pull the blower fan out- check for dirt/leaves/kleenex/ 'trash' clogged core--(no air flow thru the heater core )
 

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What did you "flush" it with? Plain water?

I have heard of others getting noticable improvement in heat if you flush it with Muriatic Acid. You can get this at most hardware stores, or a pool supply store. Pour it in, let it sit for 15-20 mins, then flush it out really good.

And pray that you don't have to pull the heater core out. You're better off selling the damn truck.
 

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Krusty said:
Pull the blower fan out- check for dirt/leaves/kleenex/ 'trash' clogged core--(no air flow thru the heater core )
This is also a really good suggestion. I had so-so heat in my old '84, till I pulled the blower motor out and reached in, found the AC evaporator coil CAKED with old dog hair, it was NASTY. It's hard to reach, but you might be able to get a shop vac in there to suck it out. My AC wasn't working anyway, so I just yanked that whole section of the ductwork out and put in a chunk from a non-AC truck, this one. Much better heat after I did that.
 

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KLF said:
And pray that you don't have to pull the heater core out. You're better off selling the damn truck.
had to help a friend pull the heater core on his old '84, something i'd never want to do again
 

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Discussion Starter #6
I checked the blend door and it seems to open close ok (if that's the door near the passenger side where the other temp. control wire attaches).

I'd never heard of the blower fan symptom so I'll give that a shot. Thanks.

KLF - I flushed the core w/ garden hose water. Like I said, the water flowed quite well after the initial brown water flushed through.

Pulling the core would be the "last resort" mentioned in the title. The Chilton manual makes it look so easy. :rolleyes:

Thanks for the input. anything else?


Warren
 

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To produce heat or cold, the heater core/evap coil needs flow through it (either hot water or refrigerant) and good airflow. If your supply line going into the heater core is hot with the truck running and the heat on, and your return line is hot, you need to check your airflow as stated. If you have pulled the return/supply lines and flushed them with a hose ( I assume) and you get good flow through the core, you're not plugged up. You can try doing that again and hitting it with a shot of compressed air and see if anything comes out, but more than likely it's not going to. I don't think I'd fill my cooling system with muratic acid in strong doses, it doesn't particularily like aluminum and copper when mixed strong.:rolleyes:

How about a thicker coat and long undies?:flipoff2:
 

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KLF said:
What did you "flush" it with? Plain water?

I have heard of others getting noticable improvement in heat if you flush it with Muriatic Acid. You can get this at most hardware stores, or a pool supply store. Pour it in, let it sit for 15-20 mins, then flush it out really good.

And pray that you don't have to pull the heater core out. You're better off selling the damn truck.

I'm not sure if it was muratic acid, but I used a cooling system made by prestone that came in a yellow cardboard can and had good luck with it. The can had two different powders in it, you'd drain the cooling system, dissolve the flush powder in hot water then add to the cooling system and top off with regular water, then do the same with the other powder wich was the neutralizer. I bought it because it sounded like pretty nasty stuff :) .

Before doing the flush, I unhooked the heater hoses and used compressed air to blow water through the heater core backwards, the first couple blows did yield a good bit of crud, but the flush also gave a noticeable increase in heat.
 

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If nothing else works take the heater control valve out of the circuit. Just run hoses from the pipes directly to the core. I'm guessing you have normal airflow?
 

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EDIT: Following is in case you have no airflow.

If you have A/C, check that the A/C core is not packed with junk. On mine, I got no airflow at all. The A/C core was packed with about 1/2" of crap - leaves, pine needles, dust, dirt, grime, etc, blocking it almost completely.

It's not easy to non-destructively pull the core. I'm converting my compressor to OBA at some point anyway, so I just tore the thing out and replaced the baffle empty.
 

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Discussion Starter #11
UPDATED

I went to the Auto Hobby Club today to dig into my dash in an indoor environment.

I had some old hands there giving me some help and we tried flushing the core again. Like I said, I've already done this twice but troubleshooting led us back to the core.

We powerflushed it with a large diameter garden hose flowing pretty good and did it in reverse numerous times and I'm happy to report I have sweet heat again. ;) I've updated my personal definiton of "good flow"!

Timing couldn't be better.

Thanks for all the input.

Warren
 

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Re: UPDATED

Ed Zeppeli said:
I went to the Auto Hobby Club today to dig into my dash in an indoor environment.

I had some old hands there giving me some help and we tried flushing the core again. Like I said, I've already done this twice but troubleshooting led us back to the core.

We powerflushed it with a large diameter garden hose flowing pretty good and did it in reverse numerous times and I'm happy to report I have sweet heat again. ;) I've updated my personal definiton of "good flow"!

Timing couldn't be better.

Thanks for all the input.

Warren
if you wouldn't have fixed it i would have suggested putting the thermostat control on the dash to red... i hear it gets hotter than when its on the blue:flipoff2:
 

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I'm having this same problem, I was thinking pine needles, they're everywhere around my house. Since the heater hose fittings are a lot easier to get to, I hope that's it on mine. The temperature here was in the teens last night.
 

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Discussion Starter #14
Well good luck to ya.

The list of things I tried above is a compilation of everything I found in various searches. If it's not one of the above, it's probably the core.

Flush like a madman!

Warren
 
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