22 replies to this topic

[DClarke1954]

Slow down a bit, you are making too many assumptions. Do not assume that the sender is actually properly grounded. You seem to have a multi-meter? So you can measure resistance? If so, please disconnect the cable from the sender and measure the resistance from the sender's connector to the car ground. That's the only way to confirm, instead of assume, that the sender is having proper ground connection.

 

 

Yup, I get you.   When measuring across the one currently installed in the car ( a GTR101 sender) it shows 1,520 Ohms between connector pin and a Gnd on the car, and the same directly across the sender (case-to-electrode).

This suggests that the earth return path is GOOD.

The sender (though apparently the correct one for this cluster) does not seem to work.  Gauge doesn't move but will if I earth the sender wire.  However, I am going to cheat and just put the ignition on and pull the sender and heat it up while i earth the case/sheath.  If it then works it suggests that there is no thermostat and the oversized radiator is keeping the coolant below the operating range of the sender.
Update:

OK, I pulled the GTR101 sender out of the block and put a bung in it.
Earthed the case of the sender and stuck the sender in a cup of recently boiled water.  The gauge came up off the stop (at last) and almost to the "normal" marking.  That is where I would expect it to be hovering around.  Pulled it out the water and shoved the tip of the sender into a turbo-lighter flame for a few seconds.  Gauge moved higher to be just below the "H".

 

My Conclusion:

There probably isn't a thermostat in the engine and the oversized radiator keeps it so cool that the water never gets hot enough to register on the gauge.

I don't think that is good for the engine, so I will fit a thermostat ASAP.

 

Thanks all. 

Edited by DClarke1954, 14 March 2025 - 01:26 PM.

[stuart bowes]

It's fairly easy to see if there's a 'stat fitted, there's only three bolts holding the casing on 

 

I realise it's a bit of a pain draining down some of the coolant and then topping up again but it's not a long hard job or anything 

 

to be fair, they're not expensive and they are sort of a consumable so might as well take the chance to just put a new one in anyway (selecting the right temp range)

Edited by stuart bowes, 14 March 2025 - 12:33 PM.

[NLinPEN]

You measured 1520 Ohms, at what temperature was that? One of the earlier responses in this thread referred to test results posted in this thread:  https://www.theminif...p-sender-specs/

The graph there shows that 1500 Ohms would be appropriate if the sender was at around 10 ~ 15 degrees Celsius.

I would suggest that it is beneficial to make a second measurement. Drive the car for a while to ensure that the coolant and sender are properly warmed up. Then measure the same resistance again. You should get a result below approximately 200 Ohms. However, if you then still get a value of 1500 Ohms you know that the ground connection is not good enough.

Edited by NLinPEN, 14 March 2025 - 12:36 PM.

[DClarke1954]

You measured 1520 Ohms, at what temperature was that? One of the earlier responses in this thread referred to test results posted in this thread:  https://www.theminif...p-sender-specs/

The graph there shows that 1500 Ohms would be appropriate if the sender was at around 10 ~ 15 degrees Celsius.

I would suggest that it is beneficial to make a second measurement. Drive the car for a while to ensure that the coolant and sender are properly warmed up. Then measure the same resistance again. You should get a result below approximately 200 Ohms. However, if you then still get a value of 1500 Ohms you know that the ground connection is not good enough.

1520 is off the car and on the bench at room temperature.  Nothing to do with the car's earthing at all.  Its the same in the car from connector stud on the sensor to any ground in the engine bay.  Earth's are fine.

Thanks. 

[mbolt998]

Even with no thermostat the water would easily get hot enough to register on the gauge after running for a bit. So maybe bad grounding or something? Very strange. Anyway you should definitely put a thermostat in. It's very easy and much better for the engine if it can warm up quickly (and in colder weather it may also be intermittently opening and closing as you drive).

[DClarke1954]

The saga continues.....

 

As I had suspected there was no thermostat fitted and so the engine could never reach a proper operating temperature.

Putting the thermostat in place was no problem at all of course.

I thought that as I was going to be diving into the plumbing I might as well fit an on/off valve onto the block for the heater instead of the straight take-off pipe that was on there.

That's when the trouble started.  Someone had fitted the un-switched straight take-off with incorrect and mismatched bolts and so the new/correct heat on/off valve cannot be fastened properly.

I could get lucky and find some remaining undamaged thread down there in the block if I had longer bolts/studs.

Can anyone enlighten me as to what the thread is meant to be please because I cannot find a reference to it.

 

Many thanks in advance.

 

Dan.

[stuart bowes]

minispares seems to think 1/4" unf

 

https://www.minispar...heater-tap-stud

[Steam]

They should be studs and nuts not bolts