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Discussion Starter · #1 ·
Short version: if your heat is weak try reversing the heater hoses to back flush the core.

I have had a weak heater for a while now. The coolant has always been kept pretty clean and no heavy water was ever used. I reciently flushed out the system with 2 bottles of Prestone Super Flush, which I drove around with for 2 days. Then flushed and used Gunk Heavy Duty Radiator Flush, then used MotorMaster Flush. New Mazda t-stat was installed, it gets right up to temp.

I poured a bottle of CLR through the heater core and let it sit for 5 mins before flushing with water. After all that (and tons of fresh water flushing afterwards) I refilled with Valvoline G5.

The heater was slightly better than before but still weak. Last week the temperature hit -22C (about -8F) and I couldn't stand it anymore. I was scraping ice off the inside of the windows. I was ready to take the dashboard off and replace the heater core.

Instead, I tried reversing the hoses. It was almost instantly that the heat came back to pretty much what it was 10 years ago when I bought the car. Whatever was plugging it got flushed out. Hopefully it doesn't plug it up again.
 

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Hot damn, I'll have to try this! My heat is very very weak, to the point that I'm also considering changing the core when I swap out my dash.

Now to get my dad's truck out of the garage long enough to swap the hoses...
 

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There is another side to this though, if you dont allow your cooling system to fill up with gunk, the problem never occurs :D
 

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Discussion Starter · #7 ·
There is another side to this though, if you dont allow your cooling system to fill up with gunk, the problem never occurs :D
Great tip. This seems to be a common problem and I have never let it fill with gunk. I flushed it often, used good coolant and drove across town to use my friend's soft water, rather than the hard water in my house's well. Anyway, if yours is not flowing well, try reversing the hoses - as in, put the inlet hose on the outlet fitting, and the outlet hose on the inlet fitting.
 

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There is a reason why the manufacturers recommend that you replace the coolant about every two years, the corrosion inhibiters break down....

I have owned cars that have traveled upwards for 350kkm, and by keeping the coolant clean ( i change it about every 4 years ) I have never had an overheating problem.

You still have to be careful using any tap water, even if its relatively good, it still contains dissolved minerals which will accelerate corrosion, especially with heat and time...

demineralised or distilled water costs the best part of fuck all, so why not use it and avoid the risk.

and yeah I know what its like to get a car that someone else has owned where the cooling system hasnt been taken care of, I spent a while flushing my BG's cooling system to clean out all the rubbish, problem is that you can never get all of it out...just most, so thats why it alot better to stop it from happening in the first place (if you can)
 

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Discussion Starter · #9 ·
I agree, that's why I flush it every 2 years. The water I used is tap water but it's known for its purity and low mineral content. It is very soft water.

It's pretty hard to hook up a hose and back flush your cooling system using bottles of distilled water. I usually drain the old coolant, hook up a garden hose to a fitting on the heater line and flush the whole thing out really well with clean water. Then I pour in some flush detergent, fill it with water and let the car run at temperature for 20 minutes. Then I drain the detergent, flush it out again using the hose connection so there's nothing but clear water. Then I drain that water, fill with 50-50 coolant and water.
 

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i have very little heat, and like you, scrape ice off the inside of my windows. if i bring it into a heated garage, my windows on the inside start to rain from the moisture. lol. its bad

but my heater core i replaced last year, so i dont see how this could help my situation. ive replaced all the hoses, pulled my dual core radiator, for a smaller single core, new mazda t-stat, and radiator cap, even replaced the sending unit's seeing if that would change anything. still have very little heat. if any.
 

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Is its a genuine dual stage mazda themostat ? If yes, I probably agree with Wibla, could be a blockage in one of the pipes....

and the GD heaters dont have a valve, the water flows through the core all the time, GCs had a valve that shut off the flow when the heater was not needed, so it cant be that.

Probably what I would do, is drain the coolant, and flush the system, then hook up a garden hose to the heater return to the water pump, then see how much water flows from the heater out onto the grass (might be a bit difficult to do in a Canadian winter (or nearby)).....you could probably achieve the same results without going outside, by using a large bucket (20Litres) and a drill pump, to force some water through.

Its not a problem we really face here in Australia, or at least not for any length of time.

And as for flushing, no I never flush with distilled water, I use tap water for that, and where I live its fairly clean, however I do use demineralised water when I mix up the coolant (which I like to do myself, so I know what I am getting, I never trust premix)
 

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ive actually already flushed the motor with a garden hose when i did the water pump. and did get some nastiness out of the metal coolent pipe in front of the block.

ive used a coolent flush 3 total times while messing with either the water pump, and heater core. lastw inter i busted ass trying to get this thing to give me heat. then forget about it once it gets nice. only to be reminded again how cold hearted this bitch car is. lol
 

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I used to work at a shop and what we used to do when a vehicle would come in and the heater core was plugged was this:

1. Unhook both ends of the heater hoses as they come off the block.
2. Let the hoses drain out then take a garden hose that has good pressure with a sprayer nosal stick it the hose that connects to the most upper portion of the heater core.
3. Make sure the other hose that is not connected to nosel is pointed down or you will get drenched.
4. Start with a very light touch of water and gradually work up to about medium strength of the water pressure or half way between open and close.
5. Now take the hose out of the first hose and do it to the second hose. Repeat step 3 and 4.
6. Now go back to the first hose and start slow then give it full pressure.
7. Go to the second hose again and start slow then give it full pressure.
8. We usually did this went back and fourth a few times to make sure all the junk in the heater core got out.
9. Hook both hoses back up and what ever else you had to take off just to get to the damn things up as well. Fill it back up with coolant and bleed the system of the air.
10. Enjoy your heat again and the new found joy of doing this yourself while not paying a shop for something that easy.

I will give you just a few tips make sure not to do spray full blast on the first time because the water pressure of the garden hose is about 10x more pressure than what our cooling system see and if there is any metal or debris in there you could destroy your heater core. Be careful!

Enjoy!
 

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You dont even need to do that, the 16mm heat hose can be stretched over a 3/4 barbed fitting from there you should be able to hook it up to a regular 1/2 inch garden hose...

I'll see if I can get a photo of the one I made to do this....
 

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I know, "holy old thread!:p", but I'm tired of freezing my arse off!!:mad: It took me 10 minutes to switch these lines over, burp the system, and top off the coolant, and the difference was night and day!!:cool: I'd reccomend this right now as a temporary, (maybe permanent:shrug:), fix for chilly driving.;)
 

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I broke my heater core so I picked one up from the junkies and I flushed it with the garden hose before I put it in my car. It was awful the amount of gunk and crap that came out of it. Some one must have either mixed different coolants or used one of those bottles of stop leaks. So yer, just backing up how usefull flushing the heater can be.
 

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Also ALOT of crap came outta my intake manifold when I had it off. The brown crap just flowed out when putting water thru it the opposite way!:eek:
 
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