Heater Core Flushing - OWNED!

[izzyandsue]

Well the flush seems to have worked, was 29* this morning and it heated up much better than it has in the last two years. Not sure if it's 100% or more like 85% now but it's plenty until I can screw up the courage to change the heater core and most likely the head and head gasket too. Been hearing water rushing sounds from the heater core area still unfortunately and I think it might be combustion gasses not an air pocket. Oh well it is still much better for now. Maybe I can tear it down in summer for that rebuild.

Glad it worked, or at least you got an improvement. The water rushing sounds are normal, in my experience, you have some air to get rid off and may take some time and burping process. The plastic burping funnel, around $20, makes this an easier process. Run the engine for a good 1/2 hour, with the heater set to hot, and the burping funnel with some coolant in it. May take time, but bubbles will come out, it does take a good 30 min as I remember.

 

[Speedytech7]

Thanks again for the thread, was super helpful to know which one was the inlet and which the outlet.

 

[Buttons]

Thanks again for the thread, was super helpful to know which one was the inlet and which the outlet.

Thanks for the pictures. This is great detail. ANd im still trying to get together and find a non snowy place to do mine!

 

[pdot]

This thread is still very helpful in late 2025... I followed this guide last evening. Heater put out 65 degrees in 50 degree weather. The fluid that came out only had a bit of discoloration and a tiny bit of black sediment, but now the heater vents get to 130 degrees after about 15 minutes of warming up.

Some additional notes I experienced:
- The heater core contains surprisingly little fluid, like a cup or two at most. Definitely don't need the big jug of CLR.
- Despite the above, I had 2 full buckets of liquid after this and a lot on my garage floor. Should be a fun sloshy trip to the hazmat recycling.
- The original cotter pin clamps are indeed terrible, but I also dislike worm clamps. I happened to have a couple OEM spring clamps which fit perfectly on the hoses on the U pipe. Part number is 90467-21010. Get 4 of those to replace all for a nice upgrade.

 

[izzyandsue]

This thread is still very helpful in late 2025... I followed this guide last evening. Heater put out 65 degrees in 50 degree weather. The fluid that came out only had a bit of discoloration and a tiny bit of black sediment, but now the heater vents get to 130 degrees after about 15 minutes of warming up.

Some additional notes I experienced:
- The heater core contains surprisingly little fluid, like a cup or two at most. Definitely don't need the big jug of CLR.
- Despite the above, I had 2 full buckets of liquid after this and a lot on my garage floor. Should be a fun sloshy trip to the hazmat recycling.
- The original cotter pin clamps are indeed terrible, but I also dislike worm clamps. I happened to have a couple OEM spring clamps which fit perfectly on the hoses on the U pipe. Part number is 90467-21010. Get 4 of those to replace all for a nice upgrade.

Thank you, I cant believe it has been almost 10 years since I did this. Glad its still helping.

 

[fj40ingkc]

Thanks for the images and hose clamp part numbers, worked out well.


I used blue devil flush to help get rid of the stop leak PO used to try to stop the head-gasket issues they had, (now fixed). I used a cheap 40$ Amazon pump and ran pressure a couple directions, tried ultrasonic vibrating didn’t seem to do much. But the reverse wash removed a lot of it, likely 1/4-1/3 cup of flaky stop gasket debris. Ran pump for about 45 minutes in total with changing flow direction 3 times. Flushed with distilled water, and then re-connected

Results: heat increased to 105 degrees at vent, still not a lot but better than 60 degrees. Heater tube at firewall in reads 174 and out reads ~155 so there is heat transfer, just not much to heat the full interior (1996 lx450)

Running on low velocity fan is better temp, anything above medium drops temps into mid 80’s.

Maybe something else not allowing much heat through, but I checked the hot/cold blend door actuator and sounds like it does its job, with “thunk” sound when fully sealing.

I’ve replaced upgrading to blue fan clutch when I was replacing head and head gasket, replaced the radiator /thermostat and all hoses as well at that time.
I’ll update this if I ever figure out the issue, for now relying on heated seats front/rear

This thread is still very helpful in late 2025... I followed this guide last evening. Heater put out 65 degrees in 50 degree weather. The fluid that came out only had a bit of discoloration and a tiny bit of black sediment, but now the heater vents get to 130 degrees after about 15 minutes of warming up.

Some additional notes I experienced:
- The heater core contains surprisingly little fluid, like a cup or two at most. Definitely don't need the big jug of CLR.
- Despite the above, I had 2 full buckets of liquid after this and a lot on my garage floor. Should be a fun sloshy trip to the hazmat recycling.
- The original cotter pin clamps are indeed terrible, but I also dislike worm clamps. I happened to have a couple OEM spring clamps which fit perfectly on the hoses on the U pipe. Part number is 90467-21010. Get 4 of those to replace all for a nice upgrade.

some of the flaky stop leak removed: used coffee filter to help strain hose to 5 gallon bucket.

 

[izzyandsue]

So it has been just over 10 years since I posted this instruction out of frustration with the front heater as I was relying mostly on my rear one. So time for update. This winter we have had a pretty cold spell in North Carolina, and just wanted to say that my heater can still cook a ham in the truck. Even mornings when it was single digits outside, within 5 minutes of driving it gets up there quickly and toasty in the cabin.

Don't forget to backflush first to get the crud out, then reverse it to get the rest out, and do that back and forth a few times. That way the crap can settle and be removed with reverse flow. Also, prefilling the heater core does help with any air that can get trapped in there.

 

[Speedytech7]

I just recently did mine again with a tub of hot water and CLR and a little 12v pump to circulate it. Got a ton of stuff out but unfortuntely I think my headgasket is putting combustion gasses in the heater lines and making the main cabin core fill up with gas and causing ciorculation to mostly go through the rear heat core (which works gang busters still). Heat is hot if I keep the water pump speed up like hwy driving but unfortunately I think it is just time to do the HG finally.