1999 MG California electrical issues

[Wayne Orwig]

That's the type of ring sensor we used to use on VW's.  It's what I was thinking of when I asked about ring sensors.  We called it a thermocouple.  Wrong name?

Yes, I'm sure those are thermocouples, like used in a furnace for the safety. That wouldn't interface to the ECU which wants to see a thermistor.

[Wayne Orwig]

Would it be possible to remove the oil pressure switch and put the temperature sensor there?

I may be wrong, but since that head is not oil cooled, the oil temp and the head temp are probably not the close. Not saying it wouldn't work, just that it would be inaccurate.

[rodekyll]

 . . . which brings me back to a question I asked earlier -- is it head temp or oil temp that the later sensor location was chosen for?

[Wayne Orwig]

. . . which brings me back to a question I asked earlier -- is it head temp or oil temp that the later sensor location was chosen for?

The later one is screwed directly in the aluminum head. No oil around it. But oddly it was a plastic holder.
The earlier one was in the oily cold mayo in the valve cover.

[BigVic54]

No.  The passage for the oil pressure feed is a dead end at the switch.  It detects pressure in the system.  At that point, there is no 'circulation' of oil or of heat except over a very long period of time.  Besides, you NEED the pressure detection to save your motor.

Search for a way to put a sensor on engine metal, preferably head metal.  I don't know if the sensor values are the same but in VW days we used to put a special spark plug washer which had leads to a temperature gauge.  Like this:



Maybe Wayne can comment on the actual values.
Patrick Hayes
Fremont CA

I found several spark plug temperature sensors.  Wouldn't these read hotter than an oil sensor?

[John A]

Just put a resistor and a switch in that circuit. A fully warmed engine is X and if the switch is open the ECU sees that as a cold engine, closed its warm. On my hotrodded one I use it as a choke switch but the switch is not open when not on the resistor, it goes thru the original head temp sensor. What I don't know is if the circuit went open, does the ECU see that as a failed sensor and revert to the " limp home" mode. Maybe look at the chart and use a resistor for cold and one for hot. When I forget to turn mine off the fully warmed switch position, it won't start unless the engine is in fact warm. I get better milage if I leave the switch in the resistor position.
See chart for resistor values, I don't remember. This manual pictures the P8 computer and sensors. You have the 15M so it's slightly different
http://www.dpguzzi.com/efiman.pdf

[Kiwi_Roy]

Just put a resistor and a switch in that circuit. A fully warmed engine is X and if the switch is open the ECU sees that as a cold engine, closed its warm. 

That's a good Idea, 220 Ohms is around 100°C (212F) and 5.6 KOhms about 15°C

Wire the two resistors in series with a switch to short out the 5.6 K when hot

The 15M uses the same thermistors, the chart from VII workshop manual.

Note it also shows the sensor fitted to the head in that silly plastic adapter that crumbles, it calls it an oil temperature but it screws into a blind hole so measures head temperature.

The thermistors are available from Digikey BC2730-ND (Vishay NTCLE203E33025B0), they are 3K at 25°C, I bought a bunch a couple of years back and sent a few off to owners needing them.

[Wayne Orwig]

What I don't know is if the circuit went open, does the ECU see that as a failed sensor and revert to the " limp home" mode.

I just worked on one with an add on switch, where the switch was intermittent. It almost left the owner stranded in the middle of a vacation trip.

If you use a switch, I would use a 'cold' resistor in the circuit full time, and a parallel resistor for 'hot' mode.

And mount it where it won't fail from water and heat. Maybe one of Roy's reed switches to the fast idle lever so it is sort of automatic and waterproof.

[BigVic54]

I think I have a solution.

I found a submersible 5k thermistor that I mounted on the oil dip stick.  The wire is held to the stick with shrink wrap.  I used a Dremel to make an opening in the center of the cap and passed the wire through.  I sealed the cap with JB Weld.

By doing this I've avoided the problem of wind and weather affecting the reading.  The thermistor can't be seen. I can still check the oil level.

Thank you to everyone that offered an opinion.

[Wayne Orwig]

Interesting solution.
I suspect the heat shrink will not like that hot oil over time though

Also, the later models have the sensor in the right head. As I believe yours should be. That sensor is actually intended to be screwed into the sump into oil. I believe the same part is used by Ducati in the oil. For some reason, Guzzi wants it in the head, not in the oil. No idea why.