inconsistent heat

[80stech]

Well that is interesting, this now sounds a little bit like the other thread with the 3.0L engine. Does the V8 have a manual water pump and not an electric like the 3.0L? It does sure sound like in this case that the aux pump would be suspect. Any history of cooling system work? DIS would give choices for diagnostics and bulletins based on symptoms even if there are no codes maybe ISTA will too??

Heater valves and secondary water pump should be in the ISTA as well.

OK I see you listed some history in the first post, anything else maybe? Was this the same when the aux pump wasn't working ??

Head gasket can give those heater symptoms but you would think there would be more going on and I think both those engines are pretty bullet proof as far as that goes ??

[LightlyToasted]

Originally Posted by 80stech

Does the V8 have a manual water pump and not an electric like the 3.0L? It does sure sound like in this case that the aux pump would be suspect.

Yes, the 4.8 has a belt-driven pump.

Originally Posted by 80stech

Any history of cooling system work?

LOL. The cooling system on the N62 is basically water soluble. I've replaced everything over the past few years.

Originally Posted by 80stech

Heater valves and secondary water pump should be in the ISTA as well.

Not that I have found so far. Not sure where else to look.

Originally Posted by 80stech

OK I see you listed some history in the first post, anything else maybe? Was this the same when the aux pump wasn't working ??

Kind of the same symptoms, but, IIRC, there was no heat and not off and on heat.

Originally Posted by 80stech

Head gasket can give those heater symptoms but you would think there would be more going on and I think both those engines are pretty bullet proof as far as that goes ??

Cooling system has been pressure tested, and I use a vacuum to fill and bleed the system so the coolant is fresh and I don't suspect any air pockets in the heater core.

One thing has got me thinking. When the system started to misbehave the heater core temperatures dropped really fast and really far (80C to 5C in 5s? How is that possible?). Also, sometimes one side would drop and the other would climb, etc. Only when the heater core temperatures rose above 40C would the system start to work properly. Now I'm wondering if I have a bad ground connection somewhere.