Just tested mine following the wiki guide. From cold I was getting 1764 ohms, took it round the block a few times and when warm I got 250 ohms from the ecu plug, and at the sensor it was 250 but didn't settle and kept jumping up to 500 ish every few seconds
Is the jumping significant or do I take it the sensor and wiring is ok as the difference in resisitence is considerable to when cold?
Blue temp sensor test
Moderator: martauto
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Meatballs82
- E30 Zone Camper
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Brianmoooore
- E30 Zone Team Member
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If the 'jumping' was definitely the sensor and not poor connections to the meter, then it is definitely dud.
The cold reading you give seems very low, but conceivable if the car still had some residual heat from the last time it was used.
These sensors need to track the relationship between temperature and resistance quite accurately for an engine to work as it should, and many a dud sensor will pass the simple test described on here, although the usual failure mode is such that the simple test will detect it.
Even some new sensors of dubious origin don't track accurately enough for an engine to run properly.
I once bought a tidy, but faulty E30 2 door, that I used as one of my dailys for about three years for £400.
It had a slight misfire and hesitation when up to temperature, and hadn't been cured despite a couple of attempts by a local garage. By the time I had driven it home (stopping on the way to tighten the bolts of one wheel which was getting close to departing from the rest of the car!), I had decided that a genuine blue temp. sensor was going in. One second hand sensor later, and it was running as it should.
The cold reading you give seems very low, but conceivable if the car still had some residual heat from the last time it was used.
These sensors need to track the relationship between temperature and resistance quite accurately for an engine to work as it should, and many a dud sensor will pass the simple test described on here, although the usual failure mode is such that the simple test will detect it.
Even some new sensors of dubious origin don't track accurately enough for an engine to run properly.
I once bought a tidy, but faulty E30 2 door, that I used as one of my dailys for about three years for £400.
It had a slight misfire and hesitation when up to temperature, and hadn't been cured despite a couple of attempts by a local garage. By the time I had driven it home (stopping on the way to tighten the bolts of one wheel which was getting close to departing from the rest of the car!), I had decided that a genuine blue temp. sensor was going in. One second hand sensor later, and it was running as it should.
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Meatballs82
- E30 Zone Camper
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- Joined: Tue Jan 11, 2011 11:00 pm
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I took a few readings and made sure the contact was as good as could be. I started it from cold for a few seconds to back it out of the garage, maybe didn't leave it long enough before testing then. I'll get an OE sensor in as I know its currently sporting an aftermarket varient, fitted by me after a few months of owning the car! 
Cheers
Cheers
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Meatballs82
- E30 Zone Camper
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- Joined: Tue Jan 11, 2011 11:00 pm
- Location: Northamptonshite
Just grabbed an FAE sensor (same as one fitted to mine) off the shelf at work and tested it. A steady 1900 Ohms when cold, chucked it into a mug of hot water for a few mins (hardly an exact science I know) and it was reading 500ish but again wouldn't settle. I then tested it again with a multimeter off the shelf as well as the meter I used lastnight for continuity and got the same readings.
OEM sensor on order!
OEM sensor on order!