13 replies to this topic

[maka]

Hello guys,

 

On the mini that I bought, the water temp gauge was not working, it was an aftermarket one so I decided to replace it with a Smiths one, I also replaced the sensor. In the process I also checked the thermostat and it seems to work fine, it opens after submerging it in 90º water.

 

 

But now when I start the engine (cold start) my gauge goes to H and stays there. I'm not sure what's the issue. I would expect it to be between C and N since the engine is still cold.

 

Do you guys have any clue on what could be the issue ? Could it be the sensor cable that need replacing ?

 

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[Tornado99]

did you connect the smiths guage to the voltage stabilizer? Unlike aftermarket guages, the classic smiths use a 10v power source. You didnt state what year mini you have. If you have a center binnacle speedo then there should be a electromechanical voltage stabilizer on the. Back with 12volts coming in and 10volts coming out to the guage. Note both temp and fuel level use the 10volt output.

[maka]

Hello,

 

Yes I did connect it to the 10v coming from the voltage stabilizer (I have a center speedo). 

[Tornado99]

Then you need to confirm it is giving 10v output. They do fail.
Also you said you swapped temp sensor. Try the old one perhaps? There are two types for these cars. A black top for later and a red top for ealier minis. They give different resistance ranges.

[maka]

I used a multimeter to confirm he 10v, it seems alright. I've plugged the 10v to one of the plug in the back of the gauge. I have the black top sensor and also tried with the old one and i have the same reading. 

Could be the connector or the cable ? 

[Tornado99]

Reading full scale on the guage indicates open circuit on the wire from sensor. Check connections are clean at sender and at guage. Check resistence from batt positive to guage end of sender wire which grounds through the sender temp dependant resistor to the block.

[maka]

Thanks Tornado for the help, could you please explain me how I can do that ? And what should be my readings ?

 

Check resistence from batt positive to guage end of sender wire which grounds through the sender temp dependant resistor to the block.

[sonscar]

Surely full scale is short to earth on the sender wire?does it return if you disconnect the sensor?Steve..

[Spider]

I've found the current Mini specific Temp Senders will make these gauges in particular read hot. Also, yours having a 90⁰ Thermostat, you need a particular Sender to match that so at 90⁰, the Gauge is in the N zone.

I've obtained samples of all the 5/8" UNF Senders that I could find, for all kinds of cars, including MG and Triumphs and I haven't found one yet that's right. Lately I've been making adaptors for the genuine Smiths Sender (as these are 1/8" NPT) and they read correct - for an 82 degree thermostat.

 

About all I can suggest in your case is a gauge matcher.

[Tornado99]

Surely full scale is short to earth on the sender wire?does it return if you disconnect the sensor?Steve..

I am assuming the sender resistance increases with higher temps, giving higher guage reading. If correct, then open circuit should give full scale guage reading. If sender decreases resistance as temp goes up, then a short to ground would give full scale.

[Tornado99]

I've found the current Mini specific Temp Senders will make these gauges in particular read hot. Also, yours having a 90⁰ Thermostat, you need a particular Sender to match that so at 90⁰, the Gauge is in the N zone.

I've obtained samples of all the 5/8" UNF Senders that I could find, for all kinds of cars, including MG and Triumphs and I haven't found one yet that's right. Lately I've been making adaptors for the genuine Smiths Sender (as these are 1/8" NPT) and they read correct - for an 82 degree thermostat.

About all I can suggest in your case is a gauge matcher.

A thermostat has no affect on engine operating temp. That is determines by cooling system efficiency and engine heat generation. The thermostat just determines how quickly engine reaches normal operating temp.
My car had a bypass tube installed in place of a tstat. Guage was reading low all time so I went to investigate and found the tube, no thermostat. Removed tube and put in an 82 C tstat and temps basically stayed same but got their quicker after start up. Always good practise to test a new tsat opening temp before installing. Ive seen new ones fail.

[Spider]

A thermostat has no affect on engine operating temp.

 

 

That's only true if the engine's natural running temp exceeds that of the Thermostat cracking temperature, in which case, with these cars, there's a serious issue that needs to be resolved.

eg, I know most of my own Minis and Mokes, without a Thermostat will only get to around 50 - 55⁰ on a day of 25⁰ - 28⁰ C ambient air temps.

 

The function of the Thermostat is to get the engine up to a desired temperature and then regulate it at (or close to) that Temperature.

[Tornado99]

Thanks Tornado for the help, could you please explain me how I can do that ? And what should be my readings ?

Check resistence from batt positive to guage end of sender wire which grounds through the sender temp dependant resistor to the block.

Remove sensor wire from guage. Connect negative lead from a multimeter to that end of sender wire. Take the positive lead of multimeter and connect to a 12v positive terminal someplace. With multimeter on resistence mode, it should read some amount of resistence on the scale, not zero and not infinite. The reading should change between a cold and hot engine. That tells you the wire connection to sender is ok.
Next I would suspect the guage itself. If connections are correct, suspect the guage is faulty somehow. Have another to test with?

[Tornado99]

 

A thermostat has no affect on engine operating temp.

 

 

That's only true if the engine's natural running temp exceeds that of the Thermostat cracking temperature, in which case, with these cars, there's a serious issue that needs to be resolved.

eg, I know most of my own Minis and Mokes, without a Thermostat will only get to around 50 - 55⁰ on a day of 25⁰ - 28⁰ C ambient air temps.

 

The function of the Thermostat is to get the engine up to a desired temperature and then regulate it at (or close to) that Temperature.

 

 

Normal operating temps for most cars is 95-105 Cel (which is above the typical tstat opening temp of 80-87 C). This is where the engine achieves its best efficiency and thus lowest emissions and lowest fuel consumption. Once tstat is fully open, its the rad & fan performing most removal of engine heat. If the rad/fan cannot keep up with engine heat output, then you overheat/boil over. Typically boil over will happen around 120 Cel (assuming you've got a working pressure cap on the rad and a 50/50 mix of coolant). If the rad/fan can handle all the heat from the engine, it will keep cooling down until either engine start making more heat burden (ie reving up a big hill etc) or temps reach a point that causes tstat to begin closing again. Since  mini's with the mechanically driven fan always operating on the rad, this is likely to occur in most circumstances at reasonable ambient temps. With an electric fan that comes on/off at set temps, the tstat is less likely to be open/closing regularly to hold temps above their opening point. 

 

An engine without  a tstat or a stuck open one, may take a very long time to reach normal temps, depending on how it is driven and ambient temps etc.