[Ropeguru]

So I finally got everything with the engine cooling and brakes worked out, I think.

So the last couple of things I have on my mind are the oil pressure and rear heater.

So I am not getting any heat in the rear. When changing the heat selector I am hearing the flapper move and the air flow through the outlets change also. So I think the flapper for heating and cooling is still intact. Feeling the lines towards the back of the vehicle on the passenger side, one is hot and the other is cold. So I don't believe that the core in the rear is clogged but think that the auxiliary pump is probably bad.

Can anyone confirm?

Second is more of a curiosity. I see a huge swing in oil pressure on the gauge between idle and driving down the intersate or just around town. At times, the low side is a little lower than that show in the pic but never below first mark above low.

All other vehicles I have ever owned never show this much of a change if any. Is this normal for the 4.7 Durango motors or do I have some other issue. Vehicle has 218,000+ miles on it.

See pics for gauge readings.

 

[JDK]

It sounds like heater core clogged to me. If in line is hot and out line is not. Mechanic buddy taught me a trick. Told me to take lines loose and let it drain then take CLR cleaner and push into heater core. Let sit no longer than 7-10 minutes. Rinse out thoroughly and refill with

coolant and mix. Hook hoses back up. Then bleed all air from system as normal. If heater core was about done for it will leak so youve lost nothing but time replacing. It was likely gonna leak soon anyway.

03 durango 4x4 4.7l 545RFE

 

[Don Fox]

Rope:
Your assessment of the Aux coolant pump may be the issue. Usually they begin to leak when the go bad. Re the oil gauge, that is the way my 01 4.7 would behave, so I believe you are in good shape there.

Don

 

[JDK]

I did this. It took some time but you will be surorised the calcium buildup that comes out when rinsed.
Ive never had to the auxiliary pump yet so I dont know if that would stop heater from getting warm. I would think it may take longer to get warm but would eventually blow warm on low speed at least. If u use the CLR BE SURE NOT TI LEAVE IT TOO LONG!. Aluminum will eat away quickly .
GOOD LUCK. JDK

03 durango 4x4 4.7l 545RFE

 

[Chase300]

I can confirm oil pressure looks good...exactly how my '01 4.7L oil pressure gauge reads at idle and during driving.

 

[Volphin]

The aux coolant pump only activates at 17 mph and under. Its purpose is to make the rear heat coolant flow more efficient at low speeds, nothing else. Oh wait, they also like to crack and purge coolant. NOT a benefit. LOL