Has anyone switched the hoses on the heater core pipes, on the inner fender, to back flush the heater core? Has to have been asked before. The XJ8's have only two outlets, not the three hose set up on S Types, or older XJ8's. Do not see how it should hurt the core and the coolant through the motor should follow the same path.

 

Why not just remove the hoses and attach a garden hose to back flush any crap OUT of the system rather than recirculating it into the rad?

 

Because the max pressure that the cooling system is designed for is nowhere near the 40 PSI a garden hose puts out for starters.

 

Pressure in excess, was one of my concerns from the first thought of reversing the flow of the coolant, with the cars own power doing the flush. The auxiliary pump would stand a better chance of doing no damage with coolant as the flushing agent, than a water hose with city waters grit, as well as the 40-60 PSI of water pressure, as already mentioned.

 

Sorry 1) have you not heard of moderation? 2) unless you cap the outlet you would be hard pushed to raise that sort of pressure when the outlet is open.
By all means use the Aux pump to try to move any crud out of the system.
I have just back flushed my 52 year old ‘S’ heater core using the garden hose, I didn’t have to clamp the inlet hose on.

 

Just because you can, doesn't mean you should. WCGW with a garden hose in the engine bay? Trying to limit inlet pressure with the outlet hose off and no way of regulating the pressure through the restricted lines isn't time well spent IMO. Probably don't have much in the way of electronics in that 52 year old car. Wingman, I'd recommend you follow the procedure in the service manual.

 

I have several long sections of clear poly tubing in 5/8" and 3/4" ID from the hardware store. After disconnecting the heater hoses, I use the one that fits on the inlet and one on the outlet to purge the heater matrix with a light application of compressed air into a large bucket. I then fill the tubes with a strong mix of cooling system flushing solution.

You can hang the hoses up high and watch the level through the clear hoses.

Leave the flush mixture over night and purge the heater matrix again with a soft/controlled application of compressed air into a large bucket.

Drive the car out of the shop and gently introduce a slow flow of water from a garden hose to flush the remaining chemicals from the heater core. You do NOT need to use the full force/pressure from the hose. There should be a knob somewhere to regulate the flow!!!!!!!! Continue running water until you are satisfied that the core is clear.

The good thing about the clear poly hose is that if the core is severely clogged, the hose will 'blow-off' the connector and limit the chance of damaging anything and you will know that you have a major problem!!!!

I used to do this at the Jaguar Dealer instead of contaminating the entire cooling system with flushing compound solution as per TSB 303-11am as long as the cooling system is NOT contaminated. (different car but same principle)

I don't need the entire cooling system flushed if ONLY the heater matrix is slightly clogged.

If different coolants have been mixed, then the entire system should be flushed/decontaminated.

Use your own judgement to determine if the core is clogged. (you might even use your own lungs by blowing into the hose to determine if the core is clogged)

bob

 

Worked at a chemical plant for 37 years, have a small container of sodium hydroxide in powder form. Was the solution caustic or acidic? Read that solution was a caustic mixture somewhere it seems. Was also debating after a limited blast of air, hooking the old auxiliary pump up to the pipes in reverse. Out of, then back into a five gallon bucket, with coolant drained from radiator, and motor, that was changed a year ago. As well as just reversing the hoses on the core while running the motor. But running the motor, recycling all that crud back into the system kills that idea.Back to the other ideas, have also remembered the old advertised stuff that was used to dissolve water solids in plugged shower heads that is not toxic if memory serves. Forget the name but any big box store should have it, if not that, which commercial product is the best choice?

 

You're thinking of CLR perhaps?

 

Sorry you got me with WCGW not an acronym I’m familiar, if you cannot think to fix a drain hose to the outlet then yes it would be a silly thing to do. I had the heater core out of the car as it was quite simple to do. Anyway Motorcarman has identified the best way to go, your choice.

 

C L R That's the stuff, will it work?

 

No idea. I've read threads where people have tried it but none where anyone's had success. That said, most of the threads had fully blocked cores in the end. If your going to follow Bob's method, you might want to consider using this as a method to let it sit overnight:
The old GM solution, now banned I think?
9 dry oz of Oxalic Acid (DAP Wood Bleach)
2 dry oz of Sodium Carbonate (Arm & Hammer Super Washing Soda)

Or you might try this:

Notice at the bottom of the page, there's a link to wood bleach:-)

If it were my car, I would try Bob's process of letting it sit. I'd try the Amazon product first and then if that doesn't work, the dry compound solution.

Robman, your process works and I assume most people do the same without incident.

 

One last thought if it wasn't already on your mind. For ease of access I'd disconnect the heater hoses toward the front of the block vs. the firewall.

 

The makers of CLR suggest not using it for this purpose.

Check out FAQ for CLR https://clrbrands.com/Products/CLR-Household/CLR-Calcium-Lime-Rust-Remover. There is a response to use for automotive radiators and a response for brass, copper, or aluminum.