I really really dont want to tear my dash apart just to flush my heater core...only to find out that it possibly isnt plugged at all. So yeah, is it possible to flush it effectively from the engine compartment, like where the coolant goes through the firewall? If not, is there a way to tell if the core is truly plugged without taking **** apart?

 

Good Question...UP

 

Well you actually CAN'T flush it from inside the car. The inlet and outlet hoses are on the engine compartment side of the firewall.

Flush the coolant the regular way, keep the heater in the full on position, this will flush the entire system.

 

Actually this is a good question, especially from the electro-mechanical point of view. For example, I want to attempt to flush my heater core once I get my engine out. But I will be attempting this with a car that has no power, no battery, nothing. Now, I DID leave the heater control at the full hot position when I blew the engine....whether that makes any difference at all. I have the feeling there is likely a little servo-controlled valve that defaults to the 'closed' position when the power is removed....

My thinking was just to hook up to the heater core hoses and see what happens.

 

the heater core is just a little radiator. put a hose in one end and the water will flow out the other

 

But will it flush it if the core is plugged? Id think I would need more pressure than just what the system pushes. What I wanted to know is if I can unplug the heater core from the rest of the cooling system from the ENGINE side, and flush it with high pressure water, or air from there, without removing the core.

 

also wouldnt you want to reverse flush it??? im having poor heater issues at hte moment as well -heath

 

Yeah, it should be pretty easy to reverse-flush a heater core. I've done it on FC's while I had the engine out of the car. Just stick a spray nozzle to the passenger side outlet of the core and let 'er rip. That will get all the old coolant and most gunk out of there.

With the car in one piece, it would probably be pretty easy as well - just undo the heater hoses and get a hose goin'.

If the car has no power, just try it - if no water comes out, the valve is closed. If it is closed, hook up a battery, turn the key to On, move the temp to full hot, and shut it all down. I doubt the valve would move or anything with the power off - it's likely a motor that just moves the valve from open to closed.

Dale

 

easier just to pull the dash out....13 bolts 5 electrical connectors and its out

 

Really, there's no good reason to pull the dash for flushing the heater core. The inlet/outlet pipes are easy to get to from the firewall, and I really don't see anything else you could do with regards to flushing the system that would be better/easier with the heater core out of the car.

Dale

 

so now im wondering if a heater core can "go bad"... or if it happens much with the FD. as to my problem it could also be sediment building up inside.... in that case what would be my best bet to remidy the problem??? i was thinking about shooting some "CLR" (calcium lime rust) stuff in there (i think its normally used to clean bathrooms or something??).... anyway, are there any particular products that one would be safe to use, im attempting to disolve any buildup in there?? (CLR was the first thing that popped into my mind, but im not sure how it would react w/ rubber, or plastic, or whatever else is in the heater core).

 

I plugged mine up the 2nd time I did the block sealer deal.
Sucks too, as I had one of the seemingly few FDs that had a heater that would roast you out when you wanted.

I really DO need to study my service manual and see how the system works, see exactly how the flow into the unit is controlled.

 

pull the dash and you can get a first hand look

 

ACK! You're kidding, right? I looked at the dash removal in the service manual and it looks like an absolute BITCH to do!
You've actually done this?

 

4 times...

 

Really, I think it's just a simple valve with an actuator at the inlet to the heater core. It's not that fancy.

When doing the blockweld trick, it's a good idea to bypass the heater core. By design, the heater core has tons of small passages that can get clogged up.

I think there is some Radiator Flush stuff that Prestone makes that's supposed to eat deposits away and whatnot. Might be worth a try if it's severely blocked up. Remember, the heater is basically constructed like a radiator - even if it was out of the car, you can't exactly open it up and clean gunk from it - it's a sealed unit. If it gets REAL bad and cleaning doesn't help, I bet you can find a used one pretty easily.

Dale

 

I hooked an air compressor up to mine out of the car, and blew about 100 PSI through it... then pressure tested it, and it was fine

 

so did you see any crap fly out? im guessing anything that is clogging it up is not large particles but caked on sedement or lime or whatever. i think one would need something to dissolve that stuff (if thats what the problem is). i think thats whats going on with my heater core, as its progressivly putting out less and less heat. im going to stop by the drugstore, and check out the CLR stuff (and see if it will destroy rubber or plastic). ive tried the prestone stuff with less than satisfactory results.

any more ideas about disolving caked on buildup (if thats even the problem)??? i cant think of anything else that would clog up a radiator unless some larger particles of i dont know what got in there.

 

Well, vinegar should do the job as well, and it's probably a lot cheaper than CLR.

 

I ran a power washer thru it first, then an air compresor, and repeated that a few times....

A **** LOAD of stuff came out

 

Might anyone have advice from experience what might work best to clean a heater core?



I think, or guessing I have a coating of iron oxide presumably from the irons of the old engine on the inside of the heater core is my assumption from the few clues I have.



Read to try Vinegar and have been pumping that through the core cycling it for a few hours with a coffee filter over the outlet and get an obvious small Red particle residue in the filter, not an excessive amount, but enough to see the material is in there as a clue what might be suspect cause of poor heater core performance.



Has anyone tried an actual heater core cleaning product like Prestone AS105 Radiator Flush and Cleaner or better alternative?



I have read a couple people advocating for CLR the cleaning product.Has anyone tried this despite the warnings I read against aluminum contact even if it were flushed very well to remove any residual harm?



Is there a product or method anyone has found to work well cleaning a heater core?





To give some background, I don’t believe the heater core is clogged. It flows a 3/4” line as fast as I can push it. I dont see any significant particles coming out of the core if flushed. Coolant is in fantastic condition.



My heater has always been cool. Which I suspect is really not helped by a Thick dual pass aluminum radiator, and dual stock oil coolers and typical cruising speeds.



Testing the fluid moving through the core with a thermal probe seems to show a expected water temperature.



I have tested the flow through the core visually with clear tube, the system seems to visually work and flow great as a point of interest.



I have isolated the heater core and pumped boiling water through the core, and I still get mildly warm air. In the car this is severely reduced if I speed up allowing even more cool air over the radiator and oil coolers it seems. Best heat I can get is idling the car Parked, and its still insufficient.



I have even blocked the heat exchangers just to see if I could elevate the coolant temperatures enough to make a difference even in the dead of summer!. Nothing I have done seems to allow the heater core do the job I would like it to do, which is unfortunate in an area with common low and cool temperatures.

A very long time ago I did test the actuation of the damper doors, so I believe they are still in a completely normally operational state

Anyone get deep into making their poorly operating heater core and heating system perform at an optimal level have any advice?

 

My 1st guess on heater issues considering what you have already done would be a too low temperature or malfunctioning thermostat. Is it an OE thermostat, or some aftermarket one? The OE thermostat is made to properly circulate coolant while cold and seal off the bypass when hot.

 

Assuming that your coolant temp gets above 150 F or so when the car is warmed up, it sounds like the heater core is OK and that the problem may be with the heater's air mix actuator or the damper door(s) that it controls. It is not allowing enough air to flow through the heater core and into the cabin. The heater temp **** controls the actuator, which in turn moves the damper door to blend heated/cooled air with fresh outside air or recirculated cabin air to achieve the desired temperature. It may look like the temp **** is turned all the way to HOT, but if that actuator or its door aren't working correctly, the air sent into the cabin will never get as hot as it should.

 

^All good points.

Make sure you have the heat set to blow on the lower vents, the FD's heater isn't designed to put heat out of the face vents.

If the air mix motor is stuck/broken that will cause the heater core to not receive good air flow.

Also, in general, FD heaters kind of suck. The FC had a thermonuclear furnace of a heater, every FC I had would run you out of the car with the heat even with the engine not fully up to temp. I've never been in an FD with heat that was impressive, which is crazy considering how much heat the FD's engine puts out.

Dale

 

From reading that was a part I suspected as well.

Have several new OEM mazda thermostats, and I believe one that is supposed to help hold the engine temperature at a higher level that I have tested.

This is a problem I have tinkered with for a long time, and just revisiting it once again to see if anything new and helpful can be found.

Have tested the thermostats in temperature controlled water with a probe and they have always seemed to open and close in a reasonable way.

Just for completeness, as I would really love outside help and know this community is very capable, I do have a "special" extension spacer over the thermostat I built on my filler neck that allows more turbo cold side clearance. But as far as I can tell this should have no effect internally to impede normal operation by impinging on normal actuation of the thermostat. The spacer is ~1/2" thick and IIRC it acts as if it were the filler neck to clamp the thermostat, and the filler neck sandwiches the assembly together. Various other mods as well, but none I can think that would be obviously pertinent to hopefully help discover a solution or at least other details to look into.