TEMPERATURE GAUGE SHOWING LOWER THAN TRUE, CAN YOU REPLACE?

[Jem]

My engine is running at normal temperatures but the temp gauge rarely ventures above cool.  It did go to around normal once.....

What is the most likely cause? Sender or gauge?  If it's the gauge, can you replace just that part of the larger dial before I dig it out of the dash or is it that whole unit that needs replacing?

Thanks

[enigmas]

It's good to know that you resolved the BW35 pressure control cable issue & throttle linkage problem Jem.

Moving on:
Before assigning fault to either the temperature sender unit  or receiver/gauge you need to check the viability of the current engine coolant temperature thermostat. Also take into consideration current ambient temperatures in your region.

Coolant thermostat check.
Remove the thermostat and read it's temperature rating. This info will be stamped somewhere on the body of the unit.
The thermostat when removed should be in a closed or no-flow status.
If the thermostat's valve is open when removed from it's housing, it is faulty.
If the valve is closed check to see it's function by immersing it in a pot of boiling water. The valve should open fully and progressively quite quickly. If not it's faulty.

Check the temperature rating of the thermostat if viable. The temperature rating my be too low.

* I run both my V8 engines (1 Rover SD1 3.5 V8 & 1 P76 4.4 litre V8) at 180°F or 82°C in OZ, all year round. Ambient Summer temperatures can reach 40°C with Winter currently around 6°C - 12°C.

* Running an engine too cold promotes a mayonnaise concoction with engine oil. It is also less thermally efficient with fuel usage.

If the thermostat checks out, then a gauge or sender may be at fault.


Digital Laser Thermometer
I recently purchased one of these ($25 AUD from Ebay) handheld Digital Laser Thermometers to check the various temperatures of some systems and various components on my project engines. Accurate to + or - one degree. It certainly simplifies a lot checks whether its an engine, AirCon or tonight's roast dinner.

[Ken Nelson]

there is also a 10 volt stabilizer for the temperature gauge that might need to be replaced.

[Jem]

Thanks Vincent.  I will be posting an update on the kickdown issue.  Nearly there.  A small adjustment still to make.

Regarding the temp.  I mentioned it to the mechanic who had it for a day or two and he said it was running at a normal temperature with his laser gun so I am assuming it isn't the thermostat although I have ordered a new 82 deg one anyway just to be belt and braces about it.

So I am pretty sure I am left with the sender or the gauge.  Have ordered another sender as that's the easier end to fix lol

[Jem]

Jul 1, 2023 16:05:13 GMT Ken Nelson said:

there is also a 10 volt stabilizer for the temperature gauge that might need to be replaced.

Thanks Ken.  Where is this stabilizer?

[Phil Nottingham]

Jul 3, 2023 7:21:37 GMT Jem said:

Jul 1, 2023 16:05:13 GMT Ken Nelson said:

there is also a 10 volt stabilizer for the temperature gauge that might need to be replaced.

Thanks Ken.  Where is this stabilizer?

Faulty stabilisers will cause both temp and fuel to overread and if left will damage the gauge. It is fastened to the back of the Speedo or Triple gauge and is a small rectangular metal box

[Jem]

Jul 3, 2023 8:48:55 GMT Phil Nottingham said:

Jul 3, 2023 7:21:37 GMT Jem said:

Thanks Ken.  Where is this stabilizer?

Faulty stabilisers will cause both temp and fuel to overread and if left will damage the gauge. It is fastened to the back of the Speedo or Triple gauge and is a small rectangular metal box

Thanks Phil.  The fuel gauge works perfectly although it does seem to go down quite quickly ;^)

[Phil Nottingham]

It is not the stabiliser then - may gauge or more likely sender unless thermostat has been removed to cover up overheating

[Jem]

Jul 3, 2023 14:10:45 GMT Phil Nottingham said:

It is not the stabiliser then - may gauge or more likely sender unless thermostat has been removed to cover up overheating

sender delivered yesterday!  We shall see......

[Jem]

Jul 5, 2023 7:05:34 GMT Jem said:

Jul 3, 2023 14:10:45 GMT Phil Nottingham said:

It is not the stabiliser then - may gauge or more likely sender unless thermostat has been removed to cover up overheating

sender delivered yesterday!  We shall see......

and the winner was.........

THE SENDER!!

What a ball ache that is to change too! lol  Can't get a spanner more than an eighth of a turn and not enough room for a socket and handle.

All done and reading normal.


Thanks for your help

[Jens Munk]

Congrats! Good to know.

Mine is moving but is pointing at the C blue / N green border at normal operating temperature. A new sender will go in my next parts order....

[lagain]

But, does the needle move towards the red when she starts to get hot. If it does not there could be a problem.
My needle sits just in the green when she is running as normal. The Kenlowe fan comes on when the needle is just over half way towards the red, which is not very often. These gauges are not always very accurate.

[3litrekiwi]

I've got one of these cheap infra red thermometers too, very handy but be aware that they are not adjustable for emissivity so read a bit differently depending on the surface. Matt black surfaces will be accurate but polished or shiny metals not so much. Usually set to 0.95, which means a reading will be good on a black painted radiator. Polished aluminium on the other hand has an emissivity of around 0.05 so the same car with a flash alloy radiator ŵould read quite a different temperature. 

[Jem]

Thanks Vincent.  I replaced the sender and it runs consistently at the higher end of normal but stays there steadfastly.

Have ordered one of those laser temp thingies.  Where do you point it to get a good reading?  The block or the water hoses?

I don't know why it is showing higher than normal.  Maybe it's the sender or the gauge again??  Will see what the laser says!

[Jem]

Hi Lagain.

It goes slowly up to the higher end of normal and pretty much stays there.  So until I get this laser thermometer then I can't tell whether it is actually running hot or giving a false reading.

Where to you point yours?  Not being rude lol

[enigmas]

Ideally Rover V8s run nice around 180F mark from my experiences. Engines are supposed to run hot to be thermally efficient. Too cold and the engine oil will turn into a mayonnaise concoction. Modern EFI engines run in the range 205F -217F.

As for the digital laser thermometer aim it at the thermostat housing. Do it whilst the car is warming up. The temperature should peak just prior to the thermostat opening fully.

Ideally you want the engine to stabilise at a specific working temperature and stay there...not cycle up and down through a large range of temperature. Running without a thermostat can cause this type of situation.

If you look carefully at the top radiator hose in the picture below, just near the thermostat housing you'll see a mechanical temperature gauge. This is what I use to monitor the engine temperature in my coupe. When the engine is up to temperature the gauge reads a consistent 180°F.
I can compare this mechanical gauge to the Factory Rover gauge in the car and know where the needle should be sitting.

[lagain]

Jul 11, 2023 8:55:57 GMT Jem said:

Hi Lagain.

It goes slowly up to the higher end of normal and pretty much stays there.  So until I get this laser thermometer then I can't tell whether it is actually running hot or giving a false reading.

Where to you point yours?  Not being rude lol

Mine normally sits at about 7pm, or just in the green, but I have no silt in the cooling system to slow the flow of the coolant.
As the gauge may not be very accurate see what the temperature tester says.
If it is running hot have a look at the radiator, it may need removing, which is very easy and then give it a good flushing.
Antifreeze should be a 40 per cent of Bluecol or similar. Only use concentrate, which should be put in first and then top up with soft, or distilled water. There will always be some water left in the system so ready mixed is too weak.

[Jem]

Jul 11, 2023 16:26:56 GMT lagain said:

Jul 11, 2023 8:55:57 GMT Jem said:

Hi Lagain.

It goes slowly up to the higher end of normal and pretty much stays there.  So until I get this laser thermometer then I can't tell whether it is actually running hot or giving a false reading.

Where to you point yours?  Not being rude lol

Mine normally sits at about 7pm, or just in the green, but I have no silt in the cooling system to slow the flow of the coolant.
As the gauge may not be very accurate see what the temperature tester says.
If it is running hot have a look at the radiator, it may need removing, which is very easy and then give it a good flushing.
Antifreeze should be a 40 per cent of Bluecol or similar. Only use concentrate, which should be put in first and then top up with soft, or distilled water. There will always be some water left in the system so ready mixed is too weak.

Thanks again.  It's a new radiator.  The guy that sold it to me just put it in so I'm confident that is ok.  Waiting for the delivery of this laser thermometer so we shall see!  

[Jens Munk]

Fixed with a new sender. Used to be at the blue/green border. Now right where it should be.

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