[GSB]

Originally Posted by leif20

You know I was just thinking that. Driver's side heat is ok but passenger is tepid. I am sure there are still blockages in the core. I would expect no temperature deltas if the core was operating correctly. I did NOT fully pressurize but I did use maybe 1/3rd the pressure of the garden hose. I was anxious and worried to blow out the heater core and render my car undrivable. Garden hose pressure is 40-80psi? I am worried this will burst the heater, given typical coolant system pressures are 15psi ish.

I might speed up the process and repeat. Given i've already done it once, I don't think I need to run vinegar again for 2 hours. Maybe CLR for an hour. How much should I open the hose? I do have a regulator at the barb so i can carefully control the flow there.

Yes, a valid concern. Household water pressure is 40-80psi. That's why you never want to expose a blocked core to instant pressure from a hose.

However, it is important to note that the water pressure inside an open hose, flowing fully with no restriction at the end, will be almost 0. Only if you block the end of the hose, will the pressure inside increase rapidly to the max.

That's why it's recommended to first dissolve the gunk that binds any sediment, then use a nozzle with flow control to gradually increase flow until the core is clear of sediment and able to handle the full flow from the hose.

To prevent accidental over-pressurization, I pulled the pump tubing out of the bottom connection of the core, leaving a tube only in the top of the core. Then I made a fist around the loose end of that tube and the nozzle of the garden hose. Any sudden over-pressure situation will burst out of your fingers rather than the core. A handful of sediment popped out of the core and a second later, the core was flowing a fully open nozzle with hardly any pressure felt in my fist.

Like this... Leave a gap between tube and nozzle, then squeeze hand shut to seal...