Heater blowing only cold air!

[RTTBMW]

Hi,

Met up with 'Contours' this evening and it was the first time I have driven the car in cold weather hence the subject title. When I went to get warm air I got nothing but cold air. The temp guage is working on the dash. What I have noticed on the 325 was it warms up within 2 miles! Any suggestions what to do and look out for

regards

Richard

[Brianmoooore]

I take it that the temperature gauge is doing what it should? A common cause of no heat is an airlock at the back of the cylinder head, coupled with the temp. gauge going high. This can quickly result in a cracked cylinder head on a M20B25.
If the above isn't the cause, check that the heater hoses are the correct way around on the bulkhead. The hose from the back of the cylinder head must be fitted to the lower pipe on the bulkhead, which is the opposite way around to how they fit most naturally.
If the hoses are the correct way around, do they get hot when the engine is running?

[RTTBMW]

I take it that the temperature gauge is doing what it should? A common cause of no heat is an airlock at the back of the cylinder head, coupled with the temp. gauge going high. This can quickly result in a cracked cylinder head on a M20B25.
If the above isn't the cause, check that the heater hoses are the correct way around on the bulkhead. The hose from the back of the cylinder head must be fitted to the lower pipe on the bulkhead, which is the opposite way around to how they fit most naturally.
If the hoses are the correct way around, do they get hot when the engine is running?

Hi Brian,

I'll check this out in the morning as the weather is good all day! I did replace the coolant recently, so an air lock maybe the issue!

regards

Richard

[RTTBMW]

Hi Brian,

Here are a few pictures I took yesterday! If the pipes are okay, what is the best way to remove possble airlock!







I assume this is the area you are referring to!


regards

Richard

[Brianmoooore]

That's the hoses going onto the bulkhead stub pipes, but I can't say for certain that they are the right way around from the pics. You have the car in front of you, so you need to feel along the pipes to see where they come from.
Airlock is removed by loosening the clip to the top hose, pulling the hose just of off the stub, letting coolant (and air) flow from both sides, then pushing the hoses back on. On an M20, it helps if you remove the pressure cap on the coolant bottle, pulling the overflow hose back in from the wing, placing the end of the tube in your mouth, placing a hand flat over the neck of the bottle, and blowing gently into the tube to pressurise the system slightly.

[RTTBMW]

Do you remove two stub pipes or one. loosen cap and blow into overflow pipe to remove air.

[RTTBMW]

Do you remove two stub pipes or one. loosen cap and blow into overflow pipe to remove air.

Okay the pipe at the highest point on the engine is in the upper stubb. The lower stub connects just below the rocker cover at the very back of the engine. I pulled the upper pipe offf and it was full of coolant. The lower pipe was too. Do I chance swapping them round.

[RTTBMW]

The upper stubb pipe leads to the front of engine. Connecting I assume to the water pump. Ran the engine till up to temp but no hot air and the pipes at the Stubbs was cold.

[terryjippo]

Mate has the water pump been replaced recently?

[RTTBMW]

Mate has the water pump been replaced recently?

That’s the next thing am wondering about. If it needs replaced I will do timing belt etc as an overall.

[Brianmoooore]

The hot water for the heater flows from the back of the cylinder head, to the lower stub pipe, through the heater matrix, then back to the water pump.
From what you say above, the pipes are the correct way around. Don't swap them over, since this can damage the heater valve.
If the pipes are cold, no coolant is flowing through them and the matrix, so this appears to be why the heater doesn't work, rather than some problem with the blending flaps.
Water pump is a possibility (loose or broken up rotor), but I'd expect to see evidence of overheating on the temp. gauge as well.
You say you've replaced the coolant recently. If this wasn't done properly, with careful bleeding of the system, it may well be an airlock just big enough to kill the heater, but hopefully not big enough to damage the head. Was the car level when you changed the coolant? If it was facing downhill, then you will almost certainly get an airlock.
You just remove the top hose at the bulkhead, remove the pressure cap from the coolant bottle completely, place the palm of your hand flat across the filler neck, and then blow into the overflow pipe

[RTTBMW]

Yes the car has a one inch drop at the front. I’ll do this next weekend again. I’ll raise the car on the car lift and try again. However the car was on the car lift when I filled it last time and we rev her out for at least 15 minutes squeezing the pipes watching the coolant dropping in the reservoir. Today I did top it up a little.

[Brianmoooore]

I strongly advise against driving the car in the meantime. The M20B25 cylinder head doesn't tend to give second chances when overheated or subjected to thermal shock.

[RTTBMW]

I won’t. Giving rain all week so no chance of that. Thanks.

[RTTBMW]

Okay the car is ready for Monday to lift at the front and then flush the system out. So I remove lower pipe of the stub and the radiator. Might actually do this tomorrow if it’s that simple. Buckets to the ready then.

[Brianmoooore]

You just remove the TOP hose at the bulkhead, remove the pressure cap from the coolant bottle completely, place the palm of your hand flat across the filler neck, and then blow into the overflow pipe

[RTTBMW]

Hi Brian,

I did as you say and a lot of air did come out and coolant, but no change in the heater. So after a while I did a complete flush of the system and refilled with front end of the car in the air. Car certainly took a lot of coolant and I slowly heated the engine up. I flushed the heater matrix and a lot of coffee coloured coolant came out until it ran nearly clear. Filled two buckets full of water flushing the system. I removed the lower radiator pipe and lower stubb pipe. Replaced all the pipes back once no more coolant/water came out whether tilted or flat on the ground. Lifting the car again I refilled the system and had to top up a few times as the car heated up. Watch the temperature gauge she slowly heated up to the mid point then backed off. She did this a few times and the heater was on but no heat coming from the dash. So I drove the car for 3 miles and no coolant drop so she is at maximum level. I’m not sure now what to do next. Any suggestions. Is the matrix broken.

Regards

Richard

[BenHar]

I removed the lower radiator pipe and lower stubb pipe.

You just remove the TOP hose at the bulkhead, remove the pressure cap from the coolant bottle completely, place the palm of your hand flat across the filler neck, and then blow into the overflow pipe

[RTTBMW]

I did all that before a complete flush out and refill. Still stuck! But car itself runs the best.

[Brianmoooore]

Flushing must only be done at the bottom stub pipe. Bleeding must be done from the top stub pipe. I.e. the coolant must always flow from the bottom stub, through the matrix, and out of the top stub. There's an electric valve that shuts off the coolant totally when the temp. knob is at fully cold, and it will restrict the flow if coolant is going the wrong way, or be damaged if liquid is forced the wrong way.
Are the heater hoses still cold? There are possible faults with the heater assembly that can stop the heater producing hot air even if coolant is flowing through the matrix.
The default position of the electric valve is open. It closes only when 12 volts is applied to it, which should be only when the temp. knob is at or very near the fully cold position. Could be worth investigating this next, to make sure no one has wired the 12 volts permanently 'on' in a previous attempt to solve the problem.
Front centre console needs to come out for access.

[RTTBMW]

Heater hose still cold. I actually put the hose on the bottom stubb with the top Stubbs open. Only thing I thought was flow was slow out of the top Stubbs. Coffee colour until clear. I’ll get Paul my friend who is a auto electrician to give me a hand maybe tomorrow as he working nearby. I’ll show him your comments. If centre console comes out the welding on the floor will be done too. Does the glass have to come out for the headliner to be removed as I want to inspect the roof for rust.

Best regards

Richard.

[RTTBMW]

Hi,

I replaced the coolant and the car runs fine and no temperature issues so far. Engine heats up fairly quickly but to the mid point then backs off and on again. Issue I have is:

1. No heat from engine to interior still!

2. I'm getitng a plastic burning smell in the car. It is not strong but it is there! What can this be, that causes this smell.

regards & stay safe!

Richard

[Dlb26]

Sounds like there is still air in the system, try bleeding again until warm air comes through to the cabin. I don't want to scare you but you can risk head damage if there is a pocket of air lurking in there.
Have you raised the front end so that the bleed screw is higher?

[RTTBMW]

I raised the front end of the car 2ft off the ground when I did this! Flushed the matrix beforehand too!

[Brianmoooore]

First of all, I will echo what Dib26 says above. DO NOT run the engine for more than a minute or two if there's any chance of an airlock. These heads to not take kindly to thermal shock.
It's important to differentiate between a non working heater with no heat output, and a none working heater with no air output. The burning plastic smell you report is what I would normally associate with a seized fan motor and an overheating fan speed resistor pack. Are you sure the fan is running?
Which way did you flush the heater matrix?. It must be done with a garden hose connected to the lower pipe on the bulkhead. Connecting a hose with any pressure behind it to the top bulkhead pipe is quite likely to permanently damage the electric heater valve.

[Kalimsnor]

2. I'm getitng a plastic burning smell in the car. It is not strong but it is there! What can this be, that causes this smell.

I recognize this from when my heater motor was seized up and would barely blow at all. It was very easy to (temporarily) fix it with some WD40.

[RTTBMW]

First of all, I will echo what Dib26 says above. DO NOT run the engine for more than a minute or two if there's any chance of an airlock. These heads to not take kindly to thermal shock.
It's important to differentiate between a non working heater with no heat output, and a none working heater with no air output. The burning plastic smell you report is what I would normally associate with a seized fan motor and an overheating fan speed resistor pack. Are you sure the fan is running?
Which way did you flush the heater matrix?. It must be done with a garden hose connected to the lower pipe on the bulkhead. Connecting a hose with any pressure behind it to the top bulkhead pipe is quite likely to permanently damage the electric heater valve.

Hi Brian,

I carried out a coolant change in January as instructed to do! Emptied the car of coolant. Removed pipes (Including lower radiator pipe) and put hose on lower stub to flush the matrix out! I lifted the car up as well by 2ft at the front and flushed the car out. Orange coloured coolant came out until nearly clear! I added fresh coolant and ran the car until no more coolant could be added to ensure all air was taken out! The car has been driven 8 miles since this and the engine runs at normal temperature and backs off occasionally as normal.


This is where I am at now with this!

No warm air coming from the heater even thought the fan is at full speed! The plastic smell I am getting can be smelt in the car but also in the engine bay a little! It is not strong smell it is there!

Any suggestions and is it hard to remove matrix and fan?

Regards

Richard

[RTTBMW]

Sounds like there is still air in the system, try bleeding again until warm air comes through to the cabin. I don't want to scare you but you can risk head damage if there is a pocket of air lurking in there.
Have you raised the front end so that the bleed screw is higher?

Where is this bleed screw? Is that on the radiator?

regards

Richard

[Cloggy Saint]

The bleed screw is on top of the thermostat housing.

[RTTBMW]

The bleed screw is on top of the thermostat housing.

Thanks! I see it now. Paul is coming round tomorrow to fix a wiring issue! He said we will do a complete flush of the system. The fan speed is stronger when cold position than when I put it too full heat it has some resistance! Not much though!


regards

Richard

[Dlb26]

If the bleed screw hasn't moved in a while soak it in WD40 now so it's well soaked in by the time you want to use it.
Ask me how I know

[Cloggy Saint]

How do you know?

[Brianmoooore]

Even when you get the bleed screw to undo there's a fair chance that the hole it fills is blocked with gunge anyway. If nothing comes out, probe the hole with a strand of steel wire. Single strand from a wire brush is ideal. Not normally essential to use the bleed screw on a M20, though.
Fan motor is easy to remove. It's behind the centre panel at the back of the engine bay, and held in place with a large steel clip.

[Dlb26]

How do you know?

[RTTBMW]

Okay thanks!