Heater not as hot..

[B_Tank88]

Past few weeks the heater hasn't been as hot as it should be, and I've recently started diagnosing it.

- Turning the temperature knob varies temperature from COLD to COOL/WARM
- Getting the revs high will warm the air up a bit, then cools down shortly after
- Coolant temp needle goes to temperature and always stays there as it should
- Coolant level is good and consistent

Things tried:

- Had a look behind HVAC console. Cable linkage and adjustment all looks good.
- Bled radiator and heater core. Radiator had air in it, heater core had no air. I'm think everything is bled properly now, but no difference to heater air. Coolant level dropped after this and topped it up back to correct level
- Disconnected inlet and outlet pipes of heater core - both had water in it. Water seems to be passing through it (turned engine on and observed bleed side of heater core piping)

I'm running out of ideas. Last thing I was going to try was to flush our the heater core by sticking a jet wash into it.

Any other ideas?

[Craigjm]

Check that the thermostat is working as it should.

[Gaz mr-s]

I'd take the frunk out & check the bottom right corner of the radiator for a leak.  Also the front coolant pipes. The clips corrode. They're strong as f*** but can leak.  If the radiator gets hot I doubt it'd be the thermostat.

Don't trust the car temperature gauge, - if it moves above level there's a REAL problem.   Warmed-up & level is approx 83C. It doesn't move at 90C at least.

[Carolyn]

Low coolant level.  It needs more bleeding.

[B_Tank88]

Ok..

Having a couple of days to think about it, the way I bled the system was nowhere near like the lengthy process as described on the post in here. I feel I may have an airlock in the heater core.

So sometime this week I'll put aside some time to jack the corner up and use the rubber pipes to do a lengthy bleed.

[Gaz mr-s]

You may be right since the heating became defective.
I have read posts in different places about raising one end or the other, but personally haven't had any problems bleeding the system....never needed to touch the heater pipes. 

[normanh]

Simply check the pipes feeding and returning from the heater matrix, these should be really hot. If not its a airlock issue, the bleed point is right by the pipes. if the pipes are dam hot then i suspect that the controls in the cab are faulty, a baffle is in the wrong position blocking the hot airflow. Heaters in a 2 are very efficient, in almost 20 years never had a problem with mine - sold in August. Everyone in the thread have posted good potential cures.

Norman

[B_Tank88]

Ok, I put aside some time to look at this over the weekend.

1. Flushed out the heater core with garden hose, clipped the pipes to and from the core to minimise coolant loss. Reasonable amount of coolant came out the other side of the core when flushing and ended up with clear water.
2. Spent about an hour doing a bleed, with multiple drives and releasing air through bleed hoses. I'm convinced the system is properly flushed.
3. Once car is fully up to temp:
- Radiator is hot. Pipe on right side of radiator very hot (I assume entry to radiator) and pipe on left side is warm, with pressure (when squeezing).
- Pipes to and from the heater core are hot (very). Pressure on both hoses. No bubbles or foam left either in reservoir or heater and radiator bleeding rubber hoses.

The heater is still not as hot as it used to be.

Observations:
- Side vents are warmer than middle ones.
- Vents get a bit hotter after a previod of 'spirited driving'.
- If you leave HVAC fans on low/off, and give it a few mins, then do max fan speed - you get fairly hot air for about a minute, and then cools. - What does this mean??
- When changing between cold and hot on the temp adjuster knob, there is a difference from COLD to slightly warm. - Does this mean adjustment is working OK - it could it be it's not going to fully HOT maybe due to some blockage/abstruction..?

I have checked behind the HVAC unit and couldn't see anything odd, and saw the cable attached to the temp adjustment knob connected and moving some flap.
The air distribution adjustment knob seems to be working OK as far as I can tell.

[Ardent]

I was going to suggest if you could tap the matrix with a small hammer or something just to check no internal flaps had stuck in position.

[Joesson]

@B_Tank88

Reverse flushing the heater core may have further assisted removal of any sediment but clear water in and out at same pressure should indicate a clear way..
Your reference to "heater and radiator bleeding rubber hoses."  The coolant bleeding tubes on my 2 are clear plastic, is that what you used? 
I suggest there is an airlock in the heater.

[B_Tank88]

@B_Tank88

I see no reference to your use of the heater bleeding tubes.

I used the tubes every time I bled, both tubes attached to bonnet.

[Joesson]

I used the tubes every time I bled, both tubes attached to bonnet.

Are you running the engine on a water/ anti freeze solution?
Are you being frugal with the bleeding of the heater to avoid loss of the antifreeze content?
If so try collecting the fluid from the bleed tube and let it settle to bubble free before reuse if required.
Air entrapment in any hydraulic system can sometimes be troublesome to remove and one or two bubbles at the bleed point does not mean an air free circuit.
Perseverance sometimes works.

[Ardent]

This is not one of those crazy ivac air locks is it?

Ivac? The thing at the throttle body.

[B_Tank88]

Are you running the engine on a water/ anti freeze solution?
Are you being frugal with the bleeding of the heater to avoid loss of the antifreeze content?
If so try collecting the fluid from the bleed tube and let it settle to bubble free before reuse if required.
Air entrapment in any hydraulic system can sometimes be troublesome to remove and one or two bubbles at the bleed point does not mean an air free circuit.
Perseverance sometimes works.

I'm being quite frugal to avoid too much coolant loss, yes.

I can easily use a container to catch bled coolant to circulate it more, I may try that at some point.

It's just that the stuff I am bleeding now, I'm not seeing bubbles anymore that's the thing, but no harm in collecting some liquid and rerouting it I guess.

I am using red premixed coolant solution.

[B_Tank88]

This is not one of those crazy ivac air locks is it?

Ivac? The thing at the throttle body.

No idea what this is, I'll Google it.

[Gaz mr-s]

Idle Air Control Valve, bolted onto throttle body. Coolant is pumped through it to stop fuel-freezing.
IT can be affected by air in the system, usually noted by erratic tickover, but I've not read of IT causing an air lock.

[Ardent]

That ^^^

I recall from JV thread he had a mare of a time clearing. Just me adding 2 and 2 and getting 22.

[B_Tank88]

A bit more info.

Heater still sucks.

However, today, on the way home, I put the HVAC to recirc ON.

After a couple of mins the air avtually got to hot temperature from the vents.

When I changed back to recirc off, the air will very slowly cool again.

A clue???

[SurreyMR2]

@B_Tank88

Reverse flushing the heater core may have further assisted removal of any sediment but clear water in and out at same pressure should indicate a clear way..
Your reference to "heater and radiator bleeding rubber hoses."  The coolant bleeding tubes on my 2 are clear plastic, is that what you used? 
I suggest there is an airlock in the heater.

I would also suggest reverse flushing the heater matrix. Daughters Golf had this issue and it was a blocked heater matrix.