Heating stops after about 1 hour

[PaulGover]

Every time I drive our 2008 X350 for more than about an hour, the heating seems to stop and the aircon is blowing coldish air. Not too bad, but uncomfortable on the hands. It's been like this for years - possibly since I bought the car in 2011 - but by the time I'm back at the PC I've forgotten to ask the question on the forum!

Anybody come across this or have any ideas? As far as I can tell, it's not the usual failure modes, as it delivers warm air for the first hour or so.

[BrianG]

Paul,
I don't think this is a problem as such, just the normal operation. On short trips, when the car and the air inside is cold the system piles on the heat; as the air and the body of the car warm up less heat is needed so the outlet air temperature from the vents reduces and becomes 'tepid' to the hand. You'll may find the fan slows down too, depending on the length of the trip. It's the same with the air conditioning system: if you require a temperature of say 20 deg to be maintained, the outlet air is always much colder than this until the car cools down to the required level. Then the fan slows down and the outlet air becomes noticeably warmer than before.

[iRS]

Paul
I suspect Brian is spot on, but if not, could it be the aux electric heater pump is failing after a certain time? Apparently the brushes go on them. I discovered my heating is not working the first time it got cold a few weeks ago. At the moment, my car is partially stripped under the bonnet in order to replace the pump. In my case it would appear this is indeed the problem.
Good luck
Roger

Its under the expansion tank in the gap shown in this photo.

[ptjs1]

Paul,

I can't remember from my own x350, but many cars only run a full "climate control" of the temp when the aircon is selected. Try turning the aircon off and see if heat output is then maintained. Also, is the problem only on the right-hand side of the car? If so, it may be suffering from the usual x350 heater matrix problem.

Cheers

Paul

[BrianG]

could it be the aux electric heater pump is failing after a certain time? Apparently the brushes go on them.

Roger,
I don't think bushes would fail just because of xx minutes running. I have yet to experience this on my X350 (fingers crossed!) but brushes certainly do go eventually. On my previous X308 I had to take the pump motor apart and fit makeshift brushes three times in 160K miles, as I baulked at the ridiculous price of a new pump. I found, on the X308 pump at least, that when the brushes were worn down the motor would not start, but if you gave it a rap with a screwdriver handle it would run and keep running until you next stopped the car. Of course you could only do this so many times before new brushes were required.

[PaulGover]

Thanks for the various bits on information.

FWIW, I almost always run with the aircon in full operation, but I select the "air to feet and face" flow, which takes it out of full "Auto" mode. Maybe worth seeing what happens if I engage Auto after the hour. (IMHO Auto mode (a) is too keen to enter recirculating mode when moderately hot; (b) blows too much cold air in my face and stays on too long when the car interior is hot; and (c) enables the oil-burning stove when it's subzero, and I don't like burning diesel for heat, so I just turn the heated seats on.)

I doubt it's the heater pump, at least not in a simple way, as the system definitely delivers warm air for defrost and heating for the first hour...

As for hitting it with a screwdriver handle, you can only do that so many times before needing a new screwdriver

[PaulGover]

OK, somewhat latter, I've diagnosed the problem, and yes, it's that there's no (or at least little) heat on the driver's side. The reason I hadn't noticed was my wife doesn't like wind in her face, so she aims her vents at me (why not just close them? dunno), so I'm warmed by her side. But about an hour later, the car is fully warmed through, so her side stops producing much hot air, and so my side gets cold.

IIUC the loss of heat results from a partially-blocked heater matrix. It's another one of those "sealed for life" stupidities like the "filled-for-life" gearbox. In this case, the workshop manual says to renew the coolant every 150,000 (miles or km, I forget which). In the good old days it was every 30,000 miles, and so the system would get a decent flush regularly.

From what I've read, it's unlikely that a radiator flush additive will work, but I'll try the Jaguar/Ford recommended one - rather easier than all the dismantling to replace the matrix. IIUC that has the advantage that you don't need to fully drain the cooling system - just enough to get the additive in. Then run a bit, then drain and refill as per the workshop manual (a right pain on the 2.7 diesel - it appears special handling is needed to dispel air locks).