Renault Grand Scenic 1.9 diesel

[kbdiy]

My daughter's car and a problem with the heater. Basically it randomly produces warm, occasionally hot, but mostly cool air. It started to do this back in November last year. Nothing had been done prior to this to cause it to happen.

As part of the investigation, replaced the thermostat housing complete and refilled with antifreeze for the winter. Fully bled the system according to the Renault workshop manual procedure but still it only produces warm air at best, despite being driven and fully up to temperature.

During the bleeding process, venting the heater circuit will allow hot water to flow round the matrix and produce hot air. But minutes later it will be cool again and the return pipe feels cold, so no hot water circulating. And so it goes on.

Anyone got any ideas? Water pump has been suggested but am not convinced as the cooling system itself seems to be working correctly and temperature gauge registers normal temp. The car does have air con but Renault manual doesn't reference this in the basic drain/fill/bleed process.

Stumped.

 

[Mursal]

The plastic impeller might well have come off the water pump shaft. May not cause any problems to the cooling of the engine if a convection current can be crated in the radiator.
Other than that its air locked again, or the controls are not going fully hot?

 

[Burnerman]

How many bleeding points did you find, kb?
John

 

[kbdiy]

Burnerman - Working from memory as it was a couple of weeks ago that I last worked on it, I found 3 bleed points: thermostat housing, top of the inlet manifold and heater return hose.

Mursal - interesting thought about the impeller. You're right - it is airlocked again and re-bleeding can restore the heat, for a short time, then back to square one, airlocked again. Can't understand why it would keep airlocking, and we are talking numerous times here. Controls do go to fully hot as immediately after bleeding it is red hot, but then back to cool after a short time.

Grrrrrr

 

[Burnerman]

Yep, thats the three important ones....there may be one at the top right side of the rad, too.
On early Renaults, it was important to hang the expansion bottle high to help with the bleeding, but I don't know if thats needed with the Scenic.
Did you flush the heater matrix, or have any suspicions with it being blocked?
John

 

[kbdiy]

No mention in the manual about any bleed on the rad and the return to the expansion bottle is high on the side of the rad so I suspect it is ok.

The matrix seems ok. When I bled it I kept the valve open for some considerable time to ensure there was a good flow through and it turned from slightly rusty water to clear so assumed it to be ok, plus I can get good flow from the bleed at any time so am reasonably sure it's ok, but of course, it could be kidding me.

At the moment it seems to be producing heat (nothing done to it since previous postings) so am crossing fingers it has sorted itself out, but am not entirely confident!