After stepping back and taking a deep breath, please humor me for a moment as I opine on the heater core issue. I think many of us have participated in to some extent the exchanges over the past few months, and I do have a theory I’d like to toss out here for your consideration.

Symptom: No heat (or weak heat) on the driver’s side.

Suspected culprit: Heater core clogged.

Contributing culprit: Auxiliary pump failure.

Theory: Aux pump failure goes unnoticed, slowing coolant flow through the heater core, causing core to collect particulates and eventually clog.

Basis for theory:

• Based on the back-and-forth, it seems that some have experienced success with core replacement/flush and/or aux pump repair/replacement. While heat may not be completely restored to original, sufficient heat become available to be appreciated and call the repair a success.
• The word ‘auxiliary’ would indicate that the pump is supplemental in nature. Some coolant flows even if the pump is not functioning, making it appear that the new/flushed core repair has been completely successful. Ultimately, what has been solved may be more of a symptom the degraded into a problem – clogged heater core – than the root of the problem.
• The heater core is the ideal design and location to serve as a sediment trap, and without sufficiently fast coolant flow may become clogged much more frequently than if the rest of the cooling system were in perfect working order.

Recommendation: Periodically very proper operation of the auxiliary coolant pump as its failure may not be readily apparent. Drain, flush and refill the cooling system at a regular interval – every 5 years or so – regardless of the claimed permanent nature of the orange fluid.

Feel free to offer your thoughts in response.

 

I do agree with most of your assessment. I'm dealing with the same problem. However, I thought the auxiliary pump was for when the car was at idle. If that is the case, regular driving would be sufficient to keep the core flowing. ? I'm learning these engines quickly to remedy a few issues on the "What to look out for" thread.

What baffles me is that only the drivers side will become less warm than the passenger side. Isn't the same heater core used to heat both sides?

 

I have also struggled with the heating issue, although as I've posted, mine was the opposite - the passenger side was cooler than the driver side. I took out the core and flushed it. I didn't get any big particles/gunk out of it, although I did get thin, almost tissue paper like, black stuff that flowed out. Running hot and then cold water through it, and putting my fingers on the individual vanes, I felt pretty confident it wasn't clogged. After an inspection from a Jag tech, the auxiliary pump was diagnosed as non-functioning. I replaced with a new pump, and found that, although the heat wasn't burning hot, it was significantly better than before. I also found that the air coming out of the floor vents was noticeably warmer than out of the dash vents, so I'm thinking that the next step will be the blend doors.

 

When you say Drivers side, do you mean left-hand side?

 

Yes, it does appear the coolant flows even when the auxiliary pump is dead, but there is appreciably more flow when operating properly. I think this is why many of us have called the problem fixed after flush/replacement of the core. My contention is that the failed pump, probably the result of expired brushes, is the real culprit.

 

Yes, there is only one core. But due to reduced flow, sediment begins to accumulate at the point of lowest pressure, and that is on the driver's side of the core. If the pump were operating properly, the sediment would remain stirred up and probably find another place to settle (e.g. base of radiator).

 

As Yank, that would be a 'yes.'

 

QC,


Your situation was among those that really got me thinking. You probably still have a partially clogged core, band for some reason, on the opposite side.


But I'd think you would agree that the auxiliary pump is at the center of the heating issue.


Bob

 

To refresh our memories, here's a photo of the core, partially pulled from its comfy home and one all the way out.

 

that puny little thing?

on the subject of sediment, my suggestion in the original thread was that reversing inlet and outlet hoses would keep the sediment from settling as having the inlet at the bottom would keep things stirred up.

 

From what I see analyzing the coolant flow diagram, is that the auxiliary pump pushes coolant to the water pump which then pushes the coolant around and thus to the heater core line. Thus, at idle the auxiliary coolant pump ensures enough coolant flow to the water pump so the coolant can be pushed around.

 

how difficult is it to get the core out to back-flush it; or is there an accessible connection that you could put a garden hose on? Maybe down by the aux. pump?


I've been wondering if there is room to fit a sediment trap or filter.

 

Why did they use a auxiliary pump? Why didn't they just use a high-flow/high-volume water pump?

 

LCM's posted diagram above might help understand the usefulness of an auxiliary pump. Just a lot of plumbing and some passages need more encouragement than others.


There are actually three pumps on the system by my count - main, intercooler and heater core. I suspect the intercooler circuit might experience - or may actually be and is going unnoticed - blockage if that pump were as prone to failure as is the heater core auxiliary pump.

 

Yes to both. But installing a trap might frustrate coolant flow more, especially if the aux pump isn't functioning.


As for flushing with a garden hose. Tried that, repeatedly, to no avail. Once its clogged, the remaining open passages easily handle whatever pressure you push through.

 

Having cut open a few plugged ones they packed towards the end. I would just replace it if youve taken it out. Why go through more work again later. But for those with more time than money why not soak for a day or 2 in vinegar. Does wonders on home plumbing why not the cars

 

Now for the Supercharged engines, the coolant plumbing becomes even more complicated - see below coolant flow diagram.

I do want to point out however that in both the standard 4.2L engine and the Supercharged engine, there is no "heater core" pump - meaning a pump that is dedicated to pushing coolant directly to the heater core.

The standard 4.2L engine has two pumps, which is an Auxiliary coolant flow pump that flows coolant towards the main coolant pump.

The Supercharged engine has three pumps which is an Auxiliary coolant flow pump that flows coolant towards the main coolant pump and an additional Supercharged coolant pump to cool down the two charge air cooler banks.

 

I know it is semantics but in a closed circuit if a pump pushes water it has to be replaced by something so isn't the auxiliary pump actually pulling water through the matrix?

 

Yes, the auxiliary pump is encouraging the flow of coolant. Where it is placed you could say that it is pulling as well as pushing coolant. Most people believe the auxiliary pump is only on during idling to aid in coolant flow. I can feel the pumps very slight vibration when the ignition is in the on position and I can feel it when the car is started and running at idle, but I can not tell if it is on when the engine RPM are increased as the engines vibrations take away from feeling the very slight vibration of the auxiliary pump. I have seen the auxiliary pumps fan fins and the are very small.

 

I haven't checked the electrics, but I suspect that both electric pumps are full-time on with the ignition switch. There would be little reason to build in a switch other than to add another point of possible failure and possibly extend brush life.


I do know that I had one of the hoses disconnected a while back and stitched the ignition on, and the intercooler pump sprayed coolant all over the place. I suspect if my aux pump were working properly, I might have seen even more coolant fly.


And yes, the proper title of the one pump is the 'auxiliary coolant pump.' I referred to is as it relates to the coolant circuit it supports. One electric pump ensures flow through the intercoolers and it's radiator, and the other ensures flow through the cabin comfort circuit. Hope this clarifies my use of terms.


And while I'm thinking about it, I seem to remember my interior warming up quicker what I bought my car 4 winters ago. The slower-to-warm may have been an overlooked symptom of a failing aux pump.


Bob