I have a 2004 xj6 3.0L Vin SAJAC71M14VG33903 with poor heater.
Assuming that the problem is either auxiliary pump or heater matrix I sought main dealer part prices but was informed that the pump is no longer available.
I purchased Auxiliary Coolant Flow Pump - 4.2L NA V8 - AJV8/4.2L SC V8 - AJV8/3.5L from jeep-chrysler.co.uk
The local garage was asked to fit the new pump but could not find the old pump.
Is it possible that an auxiliary pump was not fitted?
And if not, is an upgrade possible or necessary or will changing the heater matrix solve the problem.
Unless otherwise advised my next step is to revisit the main agents (with the Vin) to hopefully determine whether a pump was fitted or not.

 

Hi Brayshaw,
It seems the 3.0 does have the auxiliary coolant pump. Here is the illustration from the manual that may help.

Pete M

3.0 L Engine cooling

 

Not easy to see if you have the Bosch pump.

Put your arm down between the engine and the rad
and feel for the pump.
https://www.efisolutions.com.au/bosc...RoCoHYQAvD_BwE
Usually when the matrix is blocked or partially blocked the driver's side is cold
and the pass. side is warm.
Avoid main dealers if possible
There can be a number of faults causing the problem:
Water pump with plastic impeller failed
Plastic manifold broken inside and part blocking flow
Failed t'stat

 

Like the 4,2 seems to be left side down below coolant reservoir . Follow the hoses. Fixed with just one screw and one slide pin on to the radiator

 

Thanks - will check when I get home.

 

Thanks - a good list to work through
I may have to get back to you on 'plastic manifold'

 

What is the purpose of the "auxiliary coolant flow pump"?

 

I suspect that during development and test it was found that insufficient hot water flowed through the heater matrix - so an auxilliary pump was added to increase flow.
I understand that this pump runs continually and after 100k+ miles the brushes wear down.

 

It doesn't seem to develop much pressure

 

The pumps, either the main water pump or the auxiliary, are not there to generate pressure, but to generate flow. The pressure comes from the temperature as the coolant heats up. There is a fixed volume allowed for the coolant, and as it heats up, it wants to expand, and with no place to expand to (other than the space available in the expansion tank,) it builds pressure.

The above was my understanding of the auxiliary pump's purpose, simply to increase flow through the heater core. I didn't think it ran constantly, but I really don't know what conditions cause it to run.

 

Makes sense to me know, why the pump works the way it does,thanks.
Believe the fan runs, whenever the a/c is running.

 

if you have poor heat at cruise it needs a heater core. easy job

 

Have read it's a bit of a chore.
Should not be as drawn out of a job as the radiator was.
Or replacing an a/c compressor
What is the best approach, from inside the car?
Or from under the hood?

 

If you get heat at cruise but not at idle then it may be the aux pump. It runs all the time but is there to increase flow when the main pump is not pumping a lot at idle. Unfortunately if more heat on one side than on the other, at cruise, will be 90% the heater core blockage.

 

To leak.
Oh, sorry. Coolant flow through heater.