non-starter hints? SORTED

[hankino]

thanks Brian,
Higher resistance sends message of lower temp?
so, total resistance (ie unplugged) is stone cold, 2k2 is 'room temp', 2.7 and 3.3 are somewhere between room temp and stone cold?

looked at the sports chip. For £20 I'd want a far bigger button. Gameshow size, in metallic red, mounted on the dash. BANG it down.

[Brianmoooore]

That's about it. Full hot is somewhere around 300 ohms.
Stone cold, at this time of year is around 4000 ohms.
The ebay 'sport' button switches a small resistor in series with the sensor, rather than in parallel, to make the ECU think the engine is colder than it is. The opposite of what you are doing.

[Heyho]

Where abouts are you located Hankino? If you're anywhere near me (SE), I'd make you up a loom and fit it for you.

I forgot about finding out about genuine loom, but will try to remember tomorrow!

[hankino]

That's a very generous offer Heyho, thanks - much appreciated and I'll take you up on that if I'm struggling (I'm in East Kent, though unless you're within pushing distance I'll have to get the thing started first!)

I'll be trying the resistor route tomorrow. Been to Maplin and bought 2 each of the following 2k2, 3k3, (both 3W) and 4k7 (10W).
I'll put the meter on the bue-temp itself too (don't know why I haven't done that yet, even new it could be knackered )

OT
I bought the 4K7 in a moment of confusion - I assumed going in that 2k2 meant 2200 ohms, but the young lad in Maplin insisted it was only 220 ohms in his parts book. Just checked it with my meter, 2200 of course...it's not the shop it was

[Heyho]

Well, you can't be too far away from me, I'm just outside Canterbury.

[Speedtouch]

Small world guys, I'm just outside Canterbury too

[Brianmoooore]

And I lived up at Rough Common for a while, a long, long time ago!

[hankino]

Me too!
I'm going to throw a peace sign at every E30 I see on the road in the area. If it's you, you know what to do ..
Course, as it stands, you'll have to be driving up my road but fingers-crossed.

[hankino]

oop, got in ahead of me there, Brian
Rough Common always makes me smile.
but then so does Thong

[Speedtouch]

My brother's girlfriend lives at Rough Common, though she's surprisingly refined! I crashed a Vauxhall Cavalier there once, on a notorious corner and almost put it into someone's house

[hankino]

lol, bloody notorious corners.

[hankino]

UPDATE
tested the blue temp itself this morning - not a freezing day, but properly stone cold. Resistance was 5500!
Too high surely - Haynes says 4000-4900 - I'll see if I can get the thing started tomorrow, using one of the Maplin resistors, warm it up and test resistance at operating temp.
Light at the end of the tunnel!!

[Speedtouch]

Good luck. Which Maplin store did you use: the one in Margate or Maidstone?

[Heyho]

So, is this a local thread for local people?

Try the temp sensor, and see how you get on. If you do need any further assistance, or you want to try the mod, let me know.

I'm pretty busy at the moment (E30 engine all in bits - not actually on the road yet, and house in bits too!), but I could make up a loom up here, as it only takes a few minutes to fit.

Good luck!

[hankino]

Margate Maplin on Planet Thanet.
They do relays for autos and wire - which sort would I need for the mod, Heyho?

[Heyho]

Margate Maplin on Planet Thanet.
They do relays for autos and wire - which sort would I need for the mod, Heyho?

Just a normal automotive 4-pin relay. Something like:

http://cgi.ebay.co.uk/12V-Automotive-Re ... dZViewItem

would be just fine.

[hankino]

nice one - so 4-pin, 40A, normally open contacts - just wire it up like your diagram, splicing it into the wire that leads to the blue-temp, and running a wire down to the starter motor, and to earth.

What sort of grade wire do I need - I'll gather all the bits together. Do I need something to house the resistor?

[Brianmoooore]

Relay doesn't need to be anything heavy duty like that, although the OE BMW loom does use a standard 30A relay.
4mA rated contacts would still me many more times heavier duty than is required!
House the resistor in a piece of heatshrink sleeving.

[hankino]

right, heat-shrink sleeving on the list. Back to Maplin tomorrow - any old wire will do?

[Heyho]

Yep - pretty much any wire will be fine - there's practically no current flowing in the circuit.

You could either leave the resistor temporarily connected, until you get the value right, or make it so that it is interchangeable using crimp connectors. Don't forget that there are 2 wires going to the blue sensor, as you need to connect "across" it, to achieve the desired parallel circuit.

[hankino]

UPDATE
Success! Cold this morning the Bluetemp read 5000ohms, bunged in the 3k3 instead, and it fired up after a relatively very short period of cranking.
Let it run for a bit until just out of blue zone. Measured resistance again - 1500 or so. Plugged blue temp back in, started fine.
Let it run for a while until 'normal' (just on first temp mark, never gets much higher) - resistance now 370 or so. Will give it a good run, and check again. If it doesn't get down to 300 might it be time for another new sensor?
Whatever - I can actually use the car now. RESULT
Thanks for all your help everyone - I'm off to Maplin for my loom bits

[Brianmoooore]

Note that, if, for instance, you decide that 3.3k is the optimum starting resistance, this is NOT the value of resistor you finally use, since it will be in parallel with the blue sensor.
The formula for parallel resistors is 1/R = 1/R1 + 1/R2.
Since the temp sensor reads 5k, then the parallel resistor to get 3.3k will be: 1/R2 = 1/3 - 1/5 = 0.3 - 0.2 = 0.1, which gives R2 = 10k.

[Heyho]

You beat me to it Brian!

[Brianmoooore]

Learning that (plus a lot more) was the reason I was living in Rough Common!

[Speedtouch]

Did you attend UKC then?

[Brianmoooore]

A long, long time ago!

[Speedtouch]

Cool, me too, reading Electronics Engineering in 1990-93. Which course were you on?

[Brianmoooore]

Electronics, but exactly 20 years before you!!. I think Bob Eager's still there though. (computing)

[hankino]

Thanks - can't pretend I understand (10k and 5k make 15k.... ), but clearly another trip to Maplin required. I think 10k is their biggest resistor.

I was concerned that when the car is hot or warm, and the Bluetemp resistance drops to 300-400, this then becomes a hot-start problem - but I just did the maths.

[Brianmoooore]

k = thousand.
I think you'll find that Maplins have resistors up to at least 4.7M (4,700,000) ohms!
When the blue temp sensor reaches full temp (around 300 ohms), the 10k parallel resistance will have no significant effect at all, especially as we're considering one that is only connected in circuit by a relay when starting!

[hankino]

Yes, I was very suprised when I put 300ohms into the equation, and found how little difference the addition of 10k would make then - it's anti-intuitive, unless you actually understand the electronics (which I clearly don't!)

Now for the loom...
To avoid trailing wires all over the top of the engine, can I splice into the blue-temp somewhere other than by the sensor itself, and get a wire to the starter without actually running one to where it is located? Is there a remote point where I can break into the current loom - preferably near the relay box on the passenger wing of the engine compartment (I think there's a handy spare slot)?

[Speedtouch]

T'was a hell of a degree course, with so much 'pie in the sky' theory that I've never needed in any job or situation since (thank goodness); I amassed 5 box files full of lecture notes during it - information overload or what!

Wouldn't it be worth trying a new temp sensor first?

[hankino]

you've got a point there, Speedy - although it is new.
It doesn't seem right that it should read 5500ohms at stone cold, does it, even allowing for the weather.

Just a thought, if the coolant/water mixture was wrong - way too much coolant, say - would that allow it to attain/retain a much lower temp?

[Speedtouch]

Doubtful, it is just a thermistor that changes resistance in accordance with temperature, unless you're running some sort of 'special' coolant mix!

Are you sure it's the correct sensor for the car?

[Brianmoooore]

5500 isn't that far out from what I'd expect when the temperature gets down to around freezing.
Don't know quite what you mean about the water/coolant mix, but the answer is no! Excess antifreeze reduces the efficiency of the cooling system slightly, but not so much that you'd notice.
The coolant sensor wires and starter wires all run through the engine loom where it passes the relays on the bulkhead.