No hot air / heating in M50 swap 1985 318i

[redm50]

Hi guys, apologies if there is already a topic on this but I can't find one in the search that fixes my problem!

I have converted a 1985 318i to M50B25 NV power and the heating in the cabin doesn't work.

It's been 10 years since I did the conversion and the heating did originally work. For about 8 of those years the car hasn't been driven and about 5 of those the coolant has been pure tap water.




So far i've tried:

Drained coolant, refilled with the front end jacked up and bled the radiator as much as possible.

Removed heater control valve, bench tested with a spare battery. The unit makes a clicking noise when 12V is applied to the two pins and when I put my mouth to the end of the pipe and blow through the pipe in the direction marked by the arrow on the long plastic tube the valve is open (when no 12V is applied) and then closes when I put 12V through it, is this the way it should work??

Whilst the control valve was out I forced water through it to clear out the brown dirt that was in there, wasn't too much and it seems to flow through ok.

Also removed the heater matrix and flushed through loads of water until it ran clear. Also shook the hell out of it to get as much rusty water and crap out of it as possible.

Removed the plug/switch on top of the heater control valve when the engine is hot, no difference, still no heat in the cabin.

Tested the plug voltage reading using a multimeter by turning the heater switch on the dash control from cold (shows 12.3V) to hot (shows 0V). - it's my understanding that as you turn the dash control knob from cold to hot that it should put out a reading of 12V on cold and gradually go down to 0V but mine stays at 12 until you turn the knob about 45 degrees from the coldest setting where the voltage drops straight to 0V.

Tried swapping round the two coolant hoses that go through the firewall into the control valve and matrix, makes no difference and still no heat so I don't think i've got them the wrong way round. Swapped them back round so currently the hose that runs alongside the block and splits into a T is connected to the top of the two holes that go to the heater control valve. Either way round it doesn't make a difference to the heat in the cabin but I thought i'd try it to make sure.


Here are some pics that might be useful...

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BMW M50 coolant path.jpg

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Any help at all on this would be much appreciated as i'm running out of ideas. I'm not sure what I can test next, everything seems to be working but no heat in the cabin and it's freezing outside.

[DanThe]

Hows the water pump? 5 years with just tap water in will have caused a load of corrosion, you really ought to remove it and check it out. Can you see coolant circulating with the cap off the expansion tank?
The hoses sound like they are the right way round, can you feel heat on the pipes inside the car?

[redm50]

I will take it out tomorrow and see unless I find a easier way to test it without removing on this forum/google/youtube

I can't see anything in there, the water looks still but there is pressure in the hose when I put the cap back on, could it just be steam?

Can feel heat on the top one but I can't tell for sure if the bottom one is hot, maybe it's just warm or maybe it's just in my head but it's plastic so I know the heat wouldn't transfer through that so well as the metal top pipe

[DanThe]

With the cap removed and some revs applied you should be able to see a small spray of coolant into the expansion tank, the level should also drop as the waterpump circulates it, there is a possibility that your pump has rusted and sheared the impellor off due to having just tap water in the engine

[redm50]

I was really hoping the water pump would be the cause but it looks to be fine, no missing blades and it turns freely. I'll still replace with a new one to be safe as this one must be nearly 30 years old and the replacement is only £50. Here's a pic incase you can see something i'm missing.

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The pump was very difficult to remove. I used the 6mm bolt method but snapped one of them and had to then use fire and a flat screwdriver to prise out the other side.

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What else can I try? It feels like i've now gone through everything in the coolant system and nothing appears to be broken but there is no heating still!

Also, check out how much crap was in the thermostat housing, guess that must be deposits from the tap water built up over time. Is it possible these deposits may be blocking one of the coolant paths? And if so how would I test that?

IMG-0240.jpg

Once i've cleaned the housing out, do I need an actual thermostat gasket or am I alright to use this stuff?

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[DanThe]

Definitely buy the correct gasket, yes you could well have a blockage, id get a pressure washer in the pump/thermostat holes before putting it back together, the blockage could be in the elbow off the back of the head that feeds the heater, take the hose off and poke some wire through
Id also be flushing the radiator through while it is off

[Mike25]

Have you checked the Engine thermostat?
If it has seized open, sending water around the radiator before it gets even warm, you will struggle to get hot water into the cabin heater on a freezing cold day.

[redm50]

I don't have a pressure washer but i'll take the inlet off and hopefully will be able to reach into the hole there and have a bit of a poke around. Bought some Winns radiator flush so will give that a go once it's all reconnected.

Interesting about the thermostat as there isn't one. I do vaguely remember ages ago taking it out as I think it got stuck closed. If it's as simple a fix as that then that'll be nice, will grab one of those tomorrow and let you know, I had no idea that taking it out could affect the heating.

[redm50]

How can no thermostat stop the heating from working out of interest? I thought once the coolant heats up it will circulate everywhere it's supposed to anyway?

[DanThe]

With no thermostat the pump is moving coolant with hardly any resistance, so it wont get pushed into the heater or spray into the expansion tank, or remove all the air locks as well as a correctly put together system

[redm50]

Oh jees! Ok better put that back in then. Just boiled it in a pan of water (found it in the boot) and it's still opening so will give that a go. Going to be so happy if that was the only problem. Not sure why I took it out if it's working as it appears to be

[DanThe]

You probably took it out because it was running too hot, you want an 80 degree version

[redm50]

The one I have now has 88 degrees marked on it but the reason you suggest for removing it does ring a bell. I'll put it back together and see what happens

[redm50]

Thanks guys, after some time away from this project it turns out it was the thermostat, I now have fully working heating.

Next step a remote mount turbo, pink injectors, a remap and a welded diff! Will post soon