19 replies to this topic

[systemcp]

Hi guys need your collective thoughts and inputs. I'll give you the full story behind it all to help understand the issue.

Recent mini build back on the road Sprite 1994 1275. Everything is good passed its MOT no advisories. However driving home brimmed the tank and it was only reading half. It had a new sender so I followed the guide on here to add the voltage regulator on the back of the pcb.

Success! The guage reads the fuel right. However I now notice while driving the engine temp guage is running in the red!

So earlier I let the engine idle with the rad cap off heater valve open to see if it bubbled up. It got up to temp and back in the red no bubbles except when I turned it off it did a little bit. Squeezed all the hoses and they seem fine. Both pipes to the matrix were hot. I also took the temp of the coolant in the top of the rad immediately after switching off and it was reading 72C. The rad electric fan didn't come on that comes on at 92 off at 88 and my thermostat is 88 degree too.

Could I have a dodgy sender? Is my engine overheating? Have I done something wrong with the voltage regulator? Am I missing something?

Look forward to your suggestions and help

Edited by systemcp, 21 February 2017 - 07:40 PM.

[KernowCooper]

If you took a reading of 72c thats below the normal temperature of the thermostat so not over heating by those readings, you mention not seeing bubbles when running which is a good sign, I'd change the temp sender and re-test

[panky]

Maybe you disturbed the wiring when you fitted the new regulator and the temp gauge is shorting out.

[systemcp]

I let the engine cool for 30mins turned the ignition on and the guage was reading a tad over half way so the guage seems to be working. I would of thought if it was shorting out it would still read in the red after letting it cool which it's not.

[panky]

Yes it would read full scale if it was shorting out. Is the gauge fed through the new regulator? and is it definitely connected to the output.

Edited by panky, 21 February 2017 - 08:24 PM.

[systemcp]

It's fed to the new regulator as the fuel guage regulator controls both guages as I understand it, I beleive the connections are the correct way round as per the guide on here.

Edited by systemcp, 21 February 2017 - 08:42 PM.

[panky]

Ah yes just re-read your first post about the PCB so unlikely to get the connections mixed up - sorry. It just seems a co-incidence that it's gone weird since you did the repair. I guess the next step is to replace the sender as has been suggested to eliminate that.

[systemcp]

Cheers guys I'll give it a go and get a new sender. I'm glad I'm not going mad. I really thought it was an airlock at first but frustrating when that's not the case. As always with a mini you fix one problem and it leads you straight into another!

[Cooperman]

Get a capilliary-type temperature gauge as sold by Mini Spares. They give a reading in Degrees C and are accurate. The electric ones are very rarely accurate.

[systemcp]

I have ordered a new sender. I understand about the capillary gauges but I am trying to keep the dash as clean as possible. I am going to try one more test tonight ill boil up some water drop the sender in at a temp I can record on the thermometer (im aiming for about 80c) and then look at the guage and see what it reads. I can rule it out or confirm. When I let the engine cool for 30 mins yesterday it was warm and I could easily touch but the guage read it was at running temp (halfway) that makes me think its the sender. Also when it was red hot on the guage I could touch the thermostat housing for about 2-3 seconds so right now I'm on the sender. 

 

I will update with news as I progress thanks so far everyone! 7 years of getting it back on the road and just these few little niggles to get over.

[systemcp]

So I did a quick test another way as I want to cover all options. I boiled a kettle popped some water in a mug and put the sender in. The temp read 65 photo shows 63 but it was dropping due to a cold garage. The guage is reading quite high but not in the red. However as my stat opens up at 88 I can see how at even that temp the guage could be in the red. So is my sender faulty or has my voltage regulator fix caused the guage to read wrong?

Edited by systemcp, 22 February 2017 - 06:21 PM.

[Spider]

I have not been able to buy a Sender that's been in calibration for a long while, all the ones I've tried over the past 6 - 7 years have read hot when they weren't.

[tiger99]

Check at boiling point, which only varies slightly with air pressure if you are somewhere near sea level. That will rule out any problems with your thermometer.

It is not very hard to make an extremely accurate electronic gauge, but sadly most manufacturers don't. It is easier with a digital readout. An analogue meter movement is not cheap. But in your case the problem may just be the sensor. If you have a multimeter, measure it's electrical resistance at ambient temperature and several others. The correct curve can likely be found on the Web to check against. Cheap sensors may be all over the place...

Oh and similarly you can check the gauge out by putting several values of resistor in place of the sensor. 1% resistors are commonplace and cheap but because of the way the sensor is nonlinear, errors are highest at the top end of the range.

Another possibility is that, as was often the case in older cars, the sensor is above the thermostat and reads low because the thermostat is not opening. A daft place to put it, but that is where someone put it in about 1950 when the A series engine was designed.

One of my areas of expertise in my last job was temperature measurement and it depresses me to see how badly the automotive industry does it, even now. How about quarter of a degree max error, over at least a 25 year life, with no calibration in the factory, or ever? Probably a bit too accurate (understatement!), but could be mass produced for well under £100.

[systemcp]

thanks Tiger. Its a 1275 A+ so the sensor is int he block under the thermostat rather than above. I did read on a MGB forum about the GR101 and GR104 senders which are the same on the mini and the fact that manufacturers are producing poor senders that read higher than they should be. They recommend finding old scrap cars and nabbing their senders which are more reliable than the new. I guess one option is adding a resisitor in line so it reads a little more accurately.

Edited by systemcp, 23 February 2017 - 02:44 PM.

[Sprocket]

Is that spanner grounded to the engine? The body of the sender acts as the ground.

 

 

So I did a quick test another way as I want to cover all options. I boiled a kettle popped some water in a mug and put the sender in. The temp read 65 photo shows 63 but it was dropping due to a cold garage. The guage is reading quite high but not in the red. However as my stat opens up at 88 I can see how at even that temp the guage could be in the red. So is my sender faulty or has my voltage regulator fix caused the guage to read wrong?