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Could a water pump cause low flow to my heater?

I have flushed the entire coolant system. I replaced the oil cooler (it is in line with the heater core).
I seem to have enough flow thru the heater core. The heat is good if I run the RPM up to 3K.
Could the impelars on the pump rust out or get clogged? I have heard of this before but didn’t believe it.

Generally the impellers erode away to where they no longer move sufficient fluid.
But that generally manifests itself as an engine running too hot.

How did you determine that you have sufficient flow through the heater core?
Is the engine reaching full operating temperature? Normally, or barely?
Do you live above the 45th parallel?

Are you certain the cooling system is full? I have been able to add 2-3 quarts after a road test with these cars. As I recall the 3.5 L engine has the oil cooler problem, is that the engine you have?

What I’d check if I had that problem

  • Low coolant
  • Air in coolant
  • HVAC door(s) problem
  • Heater core needs flushing or replacement
  • Faulty thermostat
  • Faulty water pump

Have you removed the outlet of the heater core with the engine running and measure the flow rate through it? Have you measured the temperature of the coolant? Yes, the pump’s impellers can gradually erode away, even to nothing. As posted above, that usually shows up as engine overheating first. But it could show up as an hvac heating problem too I suppose.

I put a scanner on and the engine temp got to temp at a good rate. It also stayed at 190° +/- 5° .
Mechanic who flushed it said he had good flow to the heater. I have flushed water thru it myself after he did and flow seems OK.

Was the water pump driving the flushing action? Or were you using a garden hose?

yes I have the 3.5. I have filled the expansion tank. and bled out the air.

Again the heat is good if I rev it up to 3K

garden hose.

Ah, well you could still have a faulty water pump then, or some obstruction prior to the heater core. Can you come up with a method to test the water pump flow? On my Corolla I can remove the top hose on the radiator, direct the flow into a bucket, and watch how much water comes out as the engine heats up. It really pours out , quite a large volume flow.

To replace the heater core will cost $1,000. Too old to do it myself - my body just can’t bend that much to replace the heater core.

Now I can replace the water pump myself. Just have doubts about the water pump being the problem.

hmmm … well probably next step is to measure the flow rate of coolant flowing through the heater core at warm idle, and its temperature.

Water pump impellers are generally made of stainless steel or plastic, I don’t recall which this one is made of but impeller failure is unlikely.

Did you loosen the bleed valve on the water outlet while adding coolant? Keep adding coolant until the level is 1/2" from the top of the reservoir.

Yea, I find it hard to believe the impellers would wear/rust out.
I’ll keep the reservoir full and see if that helps.

Thank you and merry Christmas.

https://www.gatestechzone.com/en/problem-diagnosis/cooling-system/water-pump-failure-signs

One thing I haven’t looked at yet is the drive belt.

I get good heat at 3000 rpm - if I have some slippage from the belt that is why at low rpm I don’t have heat.