heaters not working, only bowling cold

M

mr impact

New Member
Hi guys, need some assistance on finding out why the Heaters in my P6 only blow cold. It was originally a 3500 V8 but its now been fitted with a 3.9 V8 from a Range Rover. The guy who built it said he didnt touch the heaters as he built it in the summer and didnt need them. But both pipes that go into the matrix get warm, and yet the heaters blow cold in the cabin whatever position the temp setting is on.

I have drained, flushed and refilled both the heater matrix and engine radiator, taking care not to create any air locks which Im pretty sure I dont have, but its still exactly the same. Could it be the thermostat on the engine? Although surely if the stat wasnt opening, the matrix pipes would stay cold?

What position should the mechanical arms on the side of the matrix be in for hot position? Anyone have a pic? Its as though the flap isnt letting the warm air into the car somehow. The engine seems to run fine, gets up to temp fine and stays there (the previous owner said he never had any overheating issues in the summer too). The blower works ok, just no matter what we seem to do, can only get it to blow cold air!

Any help would be great.
Nick.
 
If the thermostat wasn't opening then the engine would be running too hot, not too cold, which could be the problem in your case. You need to make sure that the engine is reaching its normal running temperature, check all the flaps in the heater to make sure they're working as they should, and if both the inlet and outlet hoses to the matrix are getting hot then the matrix needs to be removed and rodded through by a radiator specialist. One last thought, are the heater hoses fitted correctly? Top on the engine goes to the bottom on the heater.
 
The lever (right hand lever on left side of centre console) should be in the fully down position to angle the flap to direct the air through the matrix exclusively. Check the lever is proper attached to the shaft on the bulk head (behind the radio - ~8mm nut and bolt). If it is, check the lever arrangement on the side of the box in the engine bay. These lever control the various flaps inside. It's possible a link has fallen off a shaft if a little clip washer has fallen off. Reattach and see what happens.

Failing that, blocked vents or split/missing seals beneath/behind the heater box.

Michael
 
Cool, cheers will have a look over the weekend. Just had a quick glance under the bonnet and Ive got the pipe from the front of the engine (from the waterpump) going to the top of the matrix, and the water pipe from the back of the engine going to the bottom of the matrix. Is that right?
 
mr impact said:
Just had a quick glance under the bonnet and Ive got the pipe from the front of the engine (from the waterpump) going to the top of the matrix, and the water pipe from the back of the engine going to the bottom of the matrix. Is that right?
Click to expand...

That sounds to be correct.
 
You need to be aware that the flap levers positions can be a little misleading in that whilst the levers may appear to be working as expected the shafts that connect to the flaps can become loose on the actuating lever ie the flap stays either open or closed but the lever appears to move.

Graeme
 
Been having a play round with the leavers and things, managed to get warm air to come into the cabin but only by your feet. If you open the face vents at the same time, they blow cold. And I cant seem to get anything onto the screen. That was my most important position really to help with de-misting the screen. The temp leaver works fine, can control hot/cold to the feet, but the other position leaver only seems to turn off the feet and the face ones can be opened in any position but always cold, no matter what the temp leaver is doing.

So are there directional flaps behind the dashboard on these cars? Is it a dash out job? Or is it all in the engine bay? I am planning on having the dash re-wired as a few things dont work and have been bodged during its life so could try sorting the heater out at the same time, but really need some decent weather as I dont have a workshop! The blowers are either on or off, the cig lighter dosnt work, neither does the interior light and the stereo needs fitting properly so it does need some wiring work!
 
mr impact said:
If you open the face vents at the same time, they blow cold. the face ones can be opened in any position but always cold, no matter what the temp leaver is doing.
Click to expand...


They're supposed to be cold all the time, they're the fresh air vents. You only get heat to the footwell and the screen.

All the flaps are within the heater box.
 
Arr right, that explains that then. Looks like the blowers are coming on and going off of their own accord too so the wiring needs looking at for sure. At least I will have warmish feet now then! I am right in thinking there are only 3 speeds to the blowers, off, half and full? I realise the heating isnt going to be as efficient as modern cars, but hopefully on a longer drive, we should get some warm air into the cabin at least.
 
mr impact said:
I am right in thinking there are only 3 speeds to the blowers, off, half and full? I realise the heating isnt going to be as efficient as modern cars, but hopefully on a longer drive, we should get some warm air into the cabin at least.
Click to expand...

Sort of. Position 1 opens the flap a bit so you get through flow, and then posititions 2 & 3 are low and high speed on the motor.

With a new matrix fitted in a good condition and correctly set up heater box they can melt your feet. Unfortunately most of them don't.
 
All of the air going through the heater is controlled by foam faced flaps. This foam deteriorates over time and allows the air to go wherever it likes. The base of the heater box can also rot out allowing the air to escape into the engine compartment.

What is supposed to happen is this:

The right hand lever has four positions, top is off, and there is no fan and the top flap on the heater box is closed. The splines on the end of the control arm (inside the engine compartment) can fail and the air flap will not open.

Get someone to move the lever from top to position 2 and see if the top flap opens ok. It should open fully. This position has no fan assist, it just relies on the positive air pressure at the base of the screen. The screen demister should work as well as feet heat/cold and face vents, but only when moving.

Position 3 leaves the top flap where it is in its fully open position, but starts up the fan on slow speed.

Position 4, fully down, runs the fan at full speed, everything else is the same.

The earth, inside the centre console can become loose and disrupt the fan. If the fan plays up, check the connections on the lever first.

The heat control lever controls two flaps and basically directs the cold air to pass through the heater matrix. If the foam has deteriorated, this won't be very efficient and you can end up with cold air coming through, or indeed warm air coming through when set to cold. Also the splines can go on these controls, so the flaps do not open and close correctly.

Up and down air flow is controlled by a single flap at the bottom. It is either open and allows the air to pass out of the heater downwards and onto your feet, or it's closed which means the air is forced upwards and out of the screen vents.

Have a look here - viewtopic.php?f=21&t=6548&hilit=heater&start=420#p103731 down the bottom of the page to see the flaps, and here viewtopic.php?f=7&t=12593&start=0&hilit=heater#p103739

My heater is quite good now i've rebuilt it, not as good as a modern car, but quite good all the same.

Richard
 
Arr brilliant, thats just the info I was looking for! Cheers. Yeah the running gear and bodywork has been done pretty well, its just the finishing touches that needs some attention!
 
If you have the heater box out (probably best) to check flaps, replace foam.....etc, have the matrix properly rodded out as a matter of course, you won't regret it. Some people settle for a backflush with a hose. Personally, I think that's a waste of time & a missed opportunity.
 
I am curious. What does rodding out the matrix involve? I have rebuilt my heter box and i cleaned the matrix using washing machine descaler plus I straightened any blades that were bent on the matrix. I havent tested the heater capasity yet so cannot say how well it works.
Regards, Barten
 
AFAIK, it involves removal of the end tanks & physically removing any crud with a metal rod then re-soldering the tanks in place. If the matrix is too bunged up then it's replaced, as with a normal (old style) rad.
 
Rather than adding a new thread on a very similar subject I'd thought I'd tag in the end of this one (if thats ok)

All the controls on my heater work, i.e:

Fan works ok at both speeds.
Fan off, ventailiation open works - you can feel the difference when moving or not.
Switching off the air works - no air when moving.

The heater control appears to work - it has an impact on the temp being blown out.

My problem is that I only really get warm air coming out when I am cruising along! As soon as I stop in traffic and the car is idling I rapidly lose heat and end up with cold air being blown out.

My thoughts were:

1. - Thermostat stuck open - however temp gauge appears to disprove this and sits just a couple of degrees to the left of fully vertical. Perhaps a needle width to the left of vertical.
2.- Heater radiator furred up. Possible, except the car has had a bottle of dishwasher cleaner through it and I have previously flushed the heater matrix with a hose.
3.- Water pump not churning enough water through at low rpms? No belt squeal, so am thinking its not loose. Feels ok too. Could a tired pump manifest like this?
4. - Low on coolant?- This is a possibility but I do check it regularly and keep it topped off.

Did anyone notice a difference in heater performance after doing the header tank mod? Mine is almost ready to go in, just needs a few coats of black paint and some time outside without it raining! :shock:

Can the panel give me any other options to explore? As it is kind of working I will probably resist taking the heater box off for a refurb until things warm up (and dry out) a bit around here!


Cheers all

Jamie
 
Hi Jamie,

I tend to think that the most probable cause is a partial blockage of the heater matrix. With the engine idling, coolant velocity through the system slows and with an impedance to flow through the matrix, it may well stop completely within. This would mean that hot coolant is not coming through with sufficient speed, hence the hot flow of air turns to cold.

Ron.
 
Hoping it's as Ron says. We had the symptoms you describe on my dad's old BMW E36. Failed to pay it due mind until one day the radiator, which was clogged, went pop. Somehow warm coolant passed through the heater while moving, not while stationary, so it didn't seem that urgent until it did.
 
Eeek! I have a good spare that I bagged some time ago on eBay, might have to think about putting that in. Thanks for the replies everyone - appreciated!
 
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