Hot/Cold Heater Issue

[GreenFish]

Good morning,

I have a heater issues with my '00 Z3 1.9 and wondered if you guys could help.

• The heater temperature takes 20-30mins+ to go from cool/cold air to hot when the temperature control is on max (hot) setting
• The engine temperature gauge moves to the middle position but still no heat
• The heat seems to come through when I accelerate at high revs or drive at 70mph on a motorway but under normal idling conditions does not heat up
• All blowers, etc working okay, just the heat

Any thoughts? Obviously not good to have this happening at this time of year Windscreen take forever to demist.

Many thanks!

 

[colb]

First thought on your symptoms is that the thermostat has failed in the open position hence the long time its taking to reach correct temp.
that would be my first stab at solving the issue by putting in a new thermostat.
as the cooling system needs to be drained to fit the thermostat take the opportunity to flush and back flush the heater matrix by using a hose on the heater intake and outlet pipes on the engine bay bulkhead. Flush till you get a good clean flow in each direction set heater to fully hot position so the heater circuit is opened for bleeding.
When refilling get the front of the car as high as you can or parked uphill so that the filler is the highest point on the system. With the heater set to fully hot refill and run the engine with the bleed screw opened and the filler cap on. As it heats up and thermostat opens feel inlet and outlet for heat circulation in and out. Watch the bleed screw for air bubbles, when they stop do the screw up and test the heater in the car for good heat. If it still feels cold try further bleeding using the bleed screw and start deoressing the radiator hoses to add some force to the liquid to force any trapped air out.
I have had success using a cheap coolant vaccum filler kit from ebay which seems to get rid of air in the system quite well but you need a compressor to use with it.

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[t-tony]

I agree with Colin, sounds like the Thermostat is stuck open.

Tony.

 

[GreenFish]

Thanks for the quick replies.

I had "assumed" that if the thermostat was stuck open then the temp gauge would be showing non-normal readings.

 

[t-tony]

All the thermostat does is close off the circulation of the engine coolant until it reaches operating temperature. When it opens it allows circulation of the coolant. Even with no thermostat in the system the engine will eventually reach its peak operating temperature, it just takes a lot longer. The temperature gauge simply shows the current temperature of the coolant at any given time.

Tony.

 

[GreenFish]

Excellent. Thank you!

 

[GreenFish]

Right...I left this over winter and now with winter 2023 now approaching I need get this fixed. Had all summer to do this but.....

Done a bit more investigation around the solenoid heater control unit/valve. Heating was on max heat, engine and normal (middle) temp on gauge (no a/c). Air blowing cool. Checked pipes going into solenoid valve:

1. Pipe that feeds into solenoid valve - lukewarm at best
2. Pipe that comes out of solenoid valve into bulkhead - not warm
3. Pipe that comes out of bulkhead - hot

I've have not done any electrical testing on the valve connector itself.

Any ideas about what I could look at/check next?

Many thanks!

 

[Rudyrov]

There are 2 hoses coming from the engine to the heater core, one stops at the control valve and controls the flow of water to the core.
There are 2 things that affect heat, a bad control valve or air in the lines. I have had both.
After replacing the control valve I had to run the engine for quite a while to get the air out, that was last year. This year I have not tested the system yet so have no clue if it will work for me.
There are bleeding procedures in the various manuals and website articles, I would suggest starting there.

 

[jonco]

During similar problems a few years ago I temporarily by-passed the heater control valve to eliminate it from problem. You can simply i) disconnect control valve inlet hose ii) short outlet hose to bulkhead iii) connect inlet hose direct to bulkhead connection. Run engine if heater then gets hot matrix is not the problem.

 

[Rudyrov]

During similar problems a few years ago I temporarily by-passed the heater control valve to eliminate it from problem. You can simply i) disconnect control valve inlet hose ii) short outlet hose to bulkhead iii) connect inlet hose direct to bulkhead connection. Run engine if heater then gets hot matrix is not the problem.

I've done that during the summer (I live in Arizona) to increase the cold air output from the AC and to bypass a defective heater control valve.
However, this led to more air in the system that needed to be bled out when I replaced the valve. Honestly, this is another poor system to troubleshoot that our cars have. It's difficult to know if the valve works or not at times.

 

[jonco]

...However, this led to more air in the system that needed to be bled out when I replaced the valve. Honestly, this is another poor system to troubleshoot that our cars have. It's difficult to know if the valve works or not at times.

I didn't have any air problems but mine was on the M44 - with no a/c. I did it with full system and clamped hoses during quick connection/disconnection.

 

[GreenFish]

Thanks for the replies. Forgeot to mention mine is the 1.9 M44 engine.

One think that has me baffled though is why the "outlet" pipe from the bulkhead (matrix) is hot but the "inlet" pipe from solenoid to bulkhead (matrix) is cool

 

[jonco]

Thanks for the replies. Forgeot to mention mine is the 1.9 M44 engine.

One think that has me baffled though is why the "outlet" pipe from the bulkhead (matrix) is hot but the "inlet" pipe from solenoid to bulkhead (matrix) is cool

Heat transfer from engine through coolant it's only a short length - no flow through heater matrix hence cool.