11 replies to this topic

[charliedurrant]

Hi,

Quick question, has anyone used their megajolt with a temperature sensor?

I wound like to use the standard sensor but it's 12v and the megajolt expects 5v. I found this on the autosportlabs forum but the thread ended without a conclusion.

http://www.autosport...84039051d2a672d

It anyone has managed to use the standard sensor and retain the temperature gauge I'd love to know how?

Charlie

[HARBER07]

A bit of info about the car would be helpful!. You can use the standard brass sensor on the older cars, BUT you can only use it for the dash gauge OR Megajolt. Not both. If you want to use both you are going to need another sensor.

[Wil_h]

I think you are a little confused. Temperature sensors are not really rated by voltage. All they do is offer a varying resistance as the temperature changes. So as long as what ever is connected to the sensor is calibrated to know what resistance relates to what temperature you could suplly it with whatever voltage you wanted (within reason!).

Having said that, the standard mini temp sensor is a single wire item, and it's easier to use a sensor with two wires, so that the earth is run back to the MS.

The conclusion of the thread you linked to should be, you can't do it with 1 sensor, you need 2. Because you are referencing a voltage to essentially measure a resistance, if you stick two voltages on the sensor, you'll screw both measurements. remember 5v and 12v are reference voltages, not driving voltages.

I've done two installs on minis and used two different solutions. as follows:

1) used the existing temperature sensor in its existing position retained for the gauge. I then fitted an additional sensor like this http://www.efi-parts...p?productID=125 to one of these.

You need the correct hose id and thread (1/8 ntp). I put mine in the top hose, but as I have front rad, this is longer than if you have a side rad.

2) On my other installation I have no heater, so I fitted an SPI sensor in the head where the temp sensor normally fits (you'll need to seal it up, I used high-temp epoxy). Then I fitted the temp sensor for the gauge in an addapter flange that I made for the heater take off on the head.

[charliedurrant]

A bit of info about the car would be helpful!.

Just for reference, do you mean what type of sensor do I currently have?

Charlie

[charliedurrant]

I think you are a little confused.

Without a doubt!

Temperature sensors are not really rated by voltage. All they do is offer a varying resistance as the temperature changes. So as long as what ever is connected to the sensor is calibrated to know what resistance relates to what temperature you could suplly it with whatever voltage you wanted (within reason!).

Having said that, the standard mini temp sensor is a single wire item, and it's easier to use a sensor with two wires, so that the earth is run back to the MS.

The conclusion of the thread you linked to should be, you can't do it with 1 sensor, you need 2. Because you are referencing a voltage to essentially measure a resistance, if you stick two voltages on the sensor, you'll screw both measurements. remember 5v and 12v are reference voltages, not driving voltages.

So what you are saying is according to V=IR

V stays constant and I or R vary and the current mini gauge measures a change in I via R changing

I've done two installs on minis and used two different solutions. as follows:

1) used the existing temperature sensor in its existing position retained for the gauge. I then fitted an additional sensor like this http://www.efi-parts...p?productID=125 to one of these.

You need the correct hose id and thread (1/8 ntp). I put mine in the top hose, but as I have front rad, this is longer than if you have a side rad.

2) On my other installation I have no heater, so I fitted an SPI sensor in the head where the temp sensor normally fits (you'll need to seal it up, I used high-temp epoxy). Then I fitted the temp sensor for the gauge in an addapter flange that I made for the heater take off on the head.

I'm case 1), but yes I have side mounted radiator which makes fitting the sensor there a problem. You are talking about the top rad hose? Isn't that after the themostat so only receives water after the thermostat is open. I expect my assumption aboutf water flow is wrong.

Charlie

p.s. For reference for others the inline pipe adapter Wil_h is referring to is supplied by http://www.racespecperformance.com

Edited by charliedurrant, 25 November 2011 - 12:19 PM.

[Wil_h]

In theory you would want the sensor before the thermostat, but in reality it's not going to make much differance. If you are using the sensor to alter fuelling you'll just end up with a slightly different warmup scale. There is always some leakage through the stat, so it will get warm before the stat opens.

Yes V=IR. The ECU basiaclly measures the voltage drop across the sensor, which is equvalent to the resistance.

[charliedurrant]

In theory you would want the sensor before the thermostat, but in reality it's not going to make much differance. If you are using the sensor to alter fuelling you'll just end up with a slightly different warmup scale. There is always some leakage through the stat, so it will get warm before the stat opens.

Yes V=IR. The ECU basiaclly measures the voltage drop across the sensor, which is equvalent to the resistance.

Interesting all this and thanks for the detail - very much appreciated. Half the battle is finding the parts!

Primarily my thoughts were to use the temperature sensor to alter the timing when the engine is cold. But I suppose it could be used to vary it for every temperature. I was going to advance the timing by 1 degree when cold (what cold is I don't yet know!). Do dizzys take temperature into account via expansion?

I've never really looked into how the water flows in a A series. My assumption is that the pump pushes water pulling it from the bottom of the rad through the block / head and out the top through the thermostat. So hence, the thermostat will be under pump pressure and will leak as you said. My thoughts are convection would occur more readily at the bottom hose, thus since I am interested in cold starting, it would be better to tap in from the bottom, especially since there is a tight turn on the top hose there is no chance of fitting an adapter there?

Charlie

[warning634]

Hi

Can someone explain what you would gain from connecting a water temp sensor up to your megajolt? Would it just give the megajolt further information on how the engine is running etc. also what is the standard thread size for the mini temp sensor that fits in the head under the thermostat.

Thanks

Kevin

[Ethel]

There is a 5/8 unf sensor that will screw into the head with a 2 pin connector. As an alternative, you could use some of the MJ user outputs to operate one or more temperature warning lights, or even drive the gauge via a resistor array. For better resolution you could even use a PIC style board to read the MJ's serial data output, but fitting a 2nd sensor may well be less work! How about one of the thermostat sandwich plates that are tapped for a sensor?


Sensor thread is 5/8unf. Reading the temperature allows you further adjust the advance for engine warm up so you need to use the choke less.

[warning634]

Thanks Ethel

I will be fitting along with the megajolt system a ETB digidash, so I'm just trying to figure out exactly what I need in relation to gauges etc and what additional sensors I should connect up to the megajolt.

Where can I purchase the 2 pin sensor from? I have also seen that dsn classics do 5/8 sensor plate to fit on the heater water outlet on the cylinder head, might be worth it.

http://www.dsnclassi.../info_1129.html

Thanks

Kevin

[warning634]

Sorry

I mean "in relation to wiring etc" not gauges!

[charliedurrant]

There is a 5/8 unf sensor that will screw into the head with a 2 pin connector. As an alternative, you could use some of the MJ user outputs to operate one or more temperature warning lights, or even drive the gauge via a resistor array. For better resolution you could even use a PIC style board to read the MJ's serial data output, but fitting a 2nd sensor may well be less work! How about one of the thermostat sandwich plates that are tapped for a sensor?


Sensor thread is 5/8unf. Reading the temperature allows you further adjust the advance for engine warm up so you need to use the choke less.

Thanks for the comments. Thermostat sandwich plate ! Yes and that will mean I can dispense with keeping my heater open / drilling my thermostat as I don't have a bypass hose!

Thank you!

Charlie