tho1981

So I just got my 87 runner a few months ago and someone had tried to steal the radio. In the process they had jacked up the heater control unit. After much time and frustration I got it replaced. So now, I am certain that all the vents open properly and the heater control wires are connected correctly (as I had the entire dash off to cure this issue).

However, when I turn the heat to as hot as possible, it gets only a few degrees warmer. I live in San Diego, so its not a big deal, but i am going to the mountains for x-mas and would like heat. Any suggestions for troubleshooting or something I need to replace?

Any advice would be great.

Thanks in advance!

NicCantDecide

There are two things that could be the problem:

1) Your heater core has debris in the vents (leaves, dirt, maybe a squirrel). You'd have to take the dash apart again to get to it and clean it out.

2) Your heater core is actually clogged and coolant isn't flowing through as it should. You have to flush the heater core to clear it out.

I would suggest flushing the heater core first because its much easier to do than taking apart the dash and vents.

4runner_guy

I would also check your heater valve switch too. Maybe it is not opening all the way to allow the maximum amount of heat to enter your cabin.

sam333

Times 2 on the flushing. 87 is an old heater core especially if the cooling system has been neglected( rust from running water or old coolent).
Also make sure your thermostat is working so your engine gets up to proper operating temp. If its stuck open you will never get good heat when its cold outside. If engine temp gauge is about in the middle then your thermostat is probably ok.

4runner_guy

Hmm...I have my 88 4Runner and it has never been on the "normal operating temps." The gauge works of course but it never really gets past the "C" or above it. I replaced the thermostat a few months back but it still stays the same. My heater works from time to time since I have replaced the heater core. Maybe I might of installed the T-stat incorrectly? Sorry, didn't mean to thread jack.

shaeff

Always check the easiest thing first.

1) Check your coolant level. If you're very low then coolant won't circulate to the heater core, thus leaving you with no heat.

2) Make sure the heater valve is operating properly. It's right on the driver's side of the firewall. Verify that it opens and closes fully.

3) Check that your motor is actually getting up to operating temperature. If it's not, check (a) coolant level as mentioned- too low and the gauge won't read, and (b) that your thermostat isn't stuck open.

4) You can try to back-flush the heater core, use low pressure otherwise you'll pop the seals which involves removing the entire dash, support brace, etc... to replace. When back-flushing, it's imperative that you push water through the heater core the OPPOSITE way that it flows normally, hence the term [i]back[i]-flush.

sabreuk

also it could be something simple as the system needs burping as it has an airlock in it. so bleed the system though, ive also just replaced the rad cap on mine and that also makes a hell of a difference in heater working properly.

4runner_guy

The coolant levels are fine, I allowed the truck to run with the rad cap off when I got done installing the heater core to burp the system. What I have replaced so far: Heater core, radiator cap, T-stat, made sure the heater valve opens and closes, and hoses to the radiator.

Since I have replaced the heater core, I have now gotten heat back into the cabin but it isn't as hot as it should be. I check religiously every week or two to see where the coolant levels are and it always stays where it should be. In addition, I also check the reservoir tank, which is fine too.

The truck doesn't over heat at all so I'm not too sure what else to be looking for if everything checks out....

Yeah, I've done this too as well.

4runner_guy

I have already replaced my T-stat, but future reference, how would you detect if it is a faulty one or not?

sabreuk

your temp gauge will either be on cold (stuck open) hot (stuck closed) or ya could check temp of rad if its working should be hot top and warm bottom as coolant cools through rad if its all hot t stat closed temp gauge hot if its all cold t stat stuck open temp gauge cold if that makes sense. try flushing rad you might have a blockage in that mate same advice for that as doing the heater matrix be gentle flushing or you will blow seals. hope that makes sense

4runner_guy

Yeah, it makes sense what you're trying to explain. So my temp is measuring at cold because the T-stat is stuck on "Open" correct? I have done a rad flush but that was before I had heater core replaced. Well, maybe it's time for another rad flush and maybe buying a new T-stat again...and then take it from there while crossing my fingers hoping everything will work and function properly. Thanks for the much help, I will give this a try as soon as the weather gets better here.

4runner_guy

And if I do a heater core flush, I should place the garden hose on the copper pipe closest to the driver side correct or is it on the passenger side?

sabreuk

yes mate if it temp gauge is cold t stat is open to allow the hot coolant to go through the rad to cool down. if you take the both pipes off and get someone to start the truck for a few seconds one pipe will have coolant coming out of it under pressure and one should be dry ( not pumping coolant out) the one that is dry do that side first as its pushing all the crap out the way it come in. once you have clear water again do the other side until you get clear water then same on heater matrix and the rad same principle for all 3 parts. put it all back together again and bleed/burp system. also id maybe have a quick check of temp sender unit and rad fan sender switch after you are sure the system is flushed and bled properly might just be the sender units might be playing up if its the temp sender playing up it should turn the electric fan on and should constantly be running wether hot or cold. if its the other it your gauge wont work properly.

sabreuk

ooops forgot to say if elec fan is constantly running it is in effect over cooling your rad so the coolant hasnt got chance to actualy warm up properly hence luke warm air coming out your vents.

4runner_guy

Awesome! Great info man. I'll make sure to check on these areas and give a feedback once I do. By the way, where is the temp sender unit located?


*Edit: I think I have it figured out, It should have a green connector with a single wire going into it. I'll check the ohms and test it to see if it is faulty..

sabreuk

Should be near where your t stat is located you should have 2 electrical plugs with single wires coming out of them. If it's you fan running pull the fan relay out in the main fuse box, it will only turn the elec fan off but you should get warm air. Then it's replacing the sender when you get chance. Let me know how ya get on bud.

4runner_guy

Cool, I'll definitely look into it and trouble shoot it with your advise, thanks much for the help! I'll update this thread once I get finished with it.

shaeff

Agreed, try parking the truck on a hill with the nose up, rad cap off (don't burn yourself) heat on full hot and full blast on the fan. Run it at about 2k RPM. That should get rid of any air pockets in the system. Do this until the truck is fully warmed up. (operating temperature)

There is no need to backflush a brand new heater core unless you've got tons of debris floating around in your cooling system. The heater core is generally one of the highest points in the cooling system, and as such, is more likely to hold an air pocket than anyplace else.

Edit: And I highly doubt a constantly running cooling fan would cause this symptom. There's no way that fan is moving more air than driving the truck at 55mph down the highway. (which you should still have great heat while doing). Check it anyway, but I do not think that is the OP's problem.

sam333

One of the best tools you can buy for cooling system diagnostics is an IR temp gun.
It takes a little practice to know what your looking at , but you can tell accurate engine, radiator temp ,if you have a blocked radiator, heater core , working thermostat. Also works good on checking cats , exhaust gas temps.

sabreuk

Edit: And I highly doubt a constantly running cooling fan would cause this symptom. There's no way that fan is moving more air than driving the truck at 55mph down the highway. (which you should still have great heat while doing). Check it anyway, but I do not think that is the OP's problem.


I was under the impression that while he has been changing all his cooling system he wasn't doing 55mph on a highway???? He should have 2 fans one viscous and one electric the viscous on it's own is more than adequate to cool the rad the elec one is for rapid cooling if the temp goes hotter than normal to stop over heating if the elec fan is running at idle with no airflow going in to rad it will overcool the rad and blow warm air as the coolant can't get warm enough. Agreed though on burping method.