Before I throw in my new inlet manifold gasket and hopefully get the old girl running as she should I thought I would iron out a few other issues while I have access in the engine bay...
Firstly my temp gauge has never worked. When ign is turned on it moves up about 3mm and stays there. Without being able to access the brown plug sensor I felt that would be at fault, but now find that seems to be ok, as is the wiring tested at pin4 of C101 and the blue plug on the instrument cluster. The reading I am getting is between 8k and 8.5k ohms. Is this right for a working sensor? If so, I guess it is the gauge at fault after all.
Secondly I get little to no hot air from the heater blower. The valve appears to be functioning, so think maybe I have a blocked matrix or an air lock in the system. Just wondering about plus bing of the matrix hoses. I have the hose from the back of the head going to the upper pipe on the matrix, and the one from the throttle body going to the lower pipe on the matrix. This appears correct on RealOEM, though I have read they should be the other way around. This could be true as the hoses don’t look like they fit well, with the upper one linked a bit where it appears to be stretched up to the matrix. Anyone know a definitive answer on that one? Would be good to know before I pull it apart this weekend.
Thanks again guys
*FIXED* M40: quick temp sensor/ gauge / heater matrix query
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E30318iM40
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Last edited by E30318iM40 on Tue Jun 01, 2021 9:08 am, edited 1 time in total.
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Brianmoooore
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Heater hoses are the wrong way around. If it's been like that for some time, you may have damaged the valve.
I have the figures for the brown sensor written down in a folder which has gone missing, but from memory, your reading seems very high. Short the single wire to the brown sensor to body earth with the ignition on. The temp gauge should go too full hot.
I have the figures for the brown sensor written down in a folder which has gone missing, but from memory, your reading seems very high. Short the single wire to the brown sensor to body earth with the ignition on. The temp gauge should go too full hot.
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E30318iM40
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Aha, I thought they were so that’s some relief. It wasn’t me who fitted the hoses, probably not even the previous owner, so let’s hope the valve isn’t wrecked. It appears to be functioning from the controls but I’ll have a good look this weekend.
As for the temp gauge, it turns out mine is a 2-wire sensor, early engine revision I think, on the brown plug. I have tried earthing pin4 of C101 to gnd to make the gauge shoot up but it just moves 3mm and stops as usual making me think it’s not the sensor. I will get the clocks out again this weekend and bench test the gauge itself. Will also re check the ohm reading from the brown plug.
Thanks again Brian
EDIT: if the sensor does turn out be duff as well, I have a replacement but it is a single wire model. At least I have a new sensor with which to test the wiring / gauge and if it does need replacing I don’t see why I can’t rig something up or why earthing through the block shouldn’t work anyway.
As for the temp gauge, it turns out mine is a 2-wire sensor, early engine revision I think, on the brown plug. I have tried earthing pin4 of C101 to gnd to make the gauge shoot up but it just moves 3mm and stops as usual making me think it’s not the sensor. I will get the clocks out again this weekend and bench test the gauge itself. Will also re check the ohm reading from the brown plug.
Thanks again Brian
EDIT: if the sensor does turn out be duff as well, I have a replacement but it is a single wire model. At least I have a new sensor with which to test the wiring / gauge and if it does need replacing I don’t see why I can’t rig something up or why earthing through the block shouldn’t work anyway.
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Brianmoooore
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No M40 ever had a twin wire brown sensor.
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E30318iM40
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Hmm, interesting. Well this one sure does. Not only a twin wire sensor, but the wire in the loom is twin wire too. So.... what do you suppose has gone on here then?? If it was an M10 or a 42 then it would have a chain (like the other 18 BMs I’ve owned) and I would not be flinching every time o I turn the key lol
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Brianmoooore
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As long as it is changed when it should be, and not contaminated by oil leaks, a cam belt is more reliable than a less than new chain. Sprockets wear, belt pullies don't. Chains stretch, belts don't (they don't get old enough).
There's often unused second wires in parts of the wiring for the temp. sensor on M20 wiring, presumably because it would cost more to change the spec. of the looms than to continue fitting unneeded wires, but not on M40 looms.
What are the colours of the wires to your plug?
There's often unused second wires in parts of the wiring for the temp. sensor on M20 wiring, presumably because it would cost more to change the spec. of the looms than to continue fitting unneeded wires, but not on M40 looms.
What are the colours of the wires to your plug?
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E30318iM40
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Sorry for belated reply, only just had chance to work on the car this morning.
Temp sensor wire colours are Violet / Brown and Brown / White, as in below pic.
[img] https://[/img]
Violet / Brown corresponds to pin4 of C101, I assume Brown / White runs to the nearest Gnd. Pin20 of C101 is a brown earth. Earthing pin4 does not make the temp gauge move more than the usual 3mm.
The pic below shows the brown sensor multimeter reading (set to 20k) now showing 11.2k ohms this morning, higher still. The new brown sensor with the single wire, albeit at room temperature, shows roughly just 700 ohms (meter set to 2k).
[img] https://[/img]
The below pic shows my heater matrix hose plumbing as when I bought the car and the next pic shows what I’ve switched round this morning. The hoses still don’t look happy.
Temp sensor wire colours are Violet / Brown and Brown / White, as in below pic.
[img] https://[/img]
Violet / Brown corresponds to pin4 of C101, I assume Brown / White runs to the nearest Gnd. Pin20 of C101 is a brown earth. Earthing pin4 does not make the temp gauge move more than the usual 3mm.
The pic below shows the brown sensor multimeter reading (set to 20k) now showing 11.2k ohms this morning, higher still. The new brown sensor with the single wire, albeit at room temperature, shows roughly just 700 ohms (meter set to 2k).
[img] https://[/img]
The below pic shows my heater matrix hose plumbing as when I bought the car and the next pic shows what I’ve switched round this morning. The hoses still don’t look happy.
Last edited by E30318iM40 on Sun May 16, 2021 2:49 pm, edited 2 times in total.
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Brianmoooore
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Your pics. aren't showing.
Brown/violet (not violet/brown - important distinction*) is the temp. gauge wire, so it's the right one. I've looked at three M40 looms in the last week, two of which were from early M40 looms, and all are single wire to the sensor. These looms were all subcontracted to more than one supplier, so you get variations, with redundant wires and wires that were never used included in some cases. It makes no difference as far as the sensor is concerned - a single terminal sensor will earth through the block, a double terminal sensor earthed through the wire. It looks like someone may have fitted a random dual terminal sensor to your car, thinking it needed two terminals. AFAIK the dual terminal sensor was obsolete and discontinued years before the M40 was introduced.
The new sensor resistance reading sounds much more like what I remember.
Beware of the brown wire connected to pin 20 of the C101 on the body side. This is the connection that has caused severe damage to the looms of many E30s when engine looms have been changed. It was repurposed to carry 12 volts ignition switched live on cars from about facelift onwards, as part of the ABS circuitry. It's a good idea to cut the brown away from pin 20 permanently.
Yes, the heater hoses do look happier when connected the wrong way around, which is probably why they get connected wrongly so often. Back of head to lower stub.
*Wiring colours aren't random. Brown/violet indicates a wire that something will happen when you earth it (gauge goes to full). Violet/brown indicates a wire associated with an accessory, and that accessory will switch 'on' if you earth the wire.
Brown/violet (not violet/brown - important distinction*) is the temp. gauge wire, so it's the right one. I've looked at three M40 looms in the last week, two of which were from early M40 looms, and all are single wire to the sensor. These looms were all subcontracted to more than one supplier, so you get variations, with redundant wires and wires that were never used included in some cases. It makes no difference as far as the sensor is concerned - a single terminal sensor will earth through the block, a double terminal sensor earthed through the wire. It looks like someone may have fitted a random dual terminal sensor to your car, thinking it needed two terminals. AFAIK the dual terminal sensor was obsolete and discontinued years before the M40 was introduced.
The new sensor resistance reading sounds much more like what I remember.
Beware of the brown wire connected to pin 20 of the C101 on the body side. This is the connection that has caused severe damage to the looms of many E30s when engine looms have been changed. It was repurposed to carry 12 volts ignition switched live on cars from about facelift onwards, as part of the ABS circuitry. It's a good idea to cut the brown away from pin 20 permanently.
Yes, the heater hoses do look happier when connected the wrong way around, which is probably why they get connected wrongly so often. Back of head to lower stub.
*Wiring colours aren't random. Brown/violet indicates a wire that something will happen when you earth it (gauge goes to full). Violet/brown indicates a wire associated with an accessory, and that accessory will switch 'on' if you earth the wire.
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E30318iM40
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Thanks. I have updated the pics to show the matrix hoses. I noticed when removing the hoses no water spilled from either or is present in the hoses / stubs and both made a gulp of air sound when removed. I have not drained any coolant and it sits halfway up the expansion bottle when cold. I have not removed the 2-wire sensor yet, so am keen to see how much water spills from there when I do. The new single wire sensor after 5 minutes in cold water reads 1.1k ohms ish.
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Brianmoooore
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Best done with an assistant.
Connect up the lower hose and fill the coolant bottle to the top. Cut the bottom off a 2l plastic drinks bottle, stick it upside down into the coolant tank, fill it with water, holding it down to minimise leaks. Coolant should start coming from the open top stub and the disconnected hose. If one starts flowing before the other, block it with a finger. When it's flowing from both, push the hose onto the stub and tighten the hose clip.
Easier on M20, because it has an overflow pipe that you can blow into, while holding a hand flat over the top of the bottle.
Connect up the lower hose and fill the coolant bottle to the top. Cut the bottom off a 2l plastic drinks bottle, stick it upside down into the coolant tank, fill it with water, holding it down to minimise leaks. Coolant should start coming from the open top stub and the disconnected hose. If one starts flowing before the other, block it with a finger. When it's flowing from both, push the hose onto the stub and tighten the hose clip.
Easier on M20, because it has an overflow pipe that you can blow into, while holding a hand flat over the top of the bottle.
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E30318iM40
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Temp. Gauge is now working and I have lots of hot air from my heater blower, so that’s two out of two sorted.
With the pipes switched round, I did the above mentioned bleeding technique to fill the heater matrix and it worked brilliantly, but tricky with one person but doable. After draining the excess from the radiator bottle I find the whole coolant system seems to be air free now and I hasn’t needed any more bleeding so far.
I tested the new single pin temp sensor and got between 1k and 1.5k ohms all the way to pin 26 on the instrument cluster, so refitted the binnacle and hey presto.... temp gauge started to read.
The M40 is now idling calmly and running pretty well after fitting the new inlet manifold gasket. Just some fine tuning of the AFM now where I messed with it, but guess you can’t have absolutely everything in one bank holiday!
Thanks again to Brian Moore for your help mate.
With the pipes switched round, I did the above mentioned bleeding technique to fill the heater matrix and it worked brilliantly, but tricky with one person but doable. After draining the excess from the radiator bottle I find the whole coolant system seems to be air free now and I hasn’t needed any more bleeding so far.
I tested the new single pin temp sensor and got between 1k and 1.5k ohms all the way to pin 26 on the instrument cluster, so refitted the binnacle and hey presto.... temp gauge started to read.
The M40 is now idling calmly and running pretty well after fitting the new inlet manifold gasket. Just some fine tuning of the AFM now where I messed with it, but guess you can’t have absolutely everything in one bank holiday!
Thanks again to Brian Moore for your help mate.
