Automotive Gauges

Thread Starter

Danraabe

Joined Jan 3, 2021
11
I installed three gauges in my Mini Cooper. Oil pressure, Boost/Vacuum, and water temperature. I used diagrams supplied by the manufacturer and added only a tachometer rpm switch and a magnetic pickup device that reads the pulses from the trigger wire on the one of the coils.

All the gauges and other electronics work. The light up, go to ZERO at start up and return to Zero when I shut the engine off. The problem gauge is the water temperature. It’s sender is located in the coolant line with the hottest water traveling to the top of the radiator after the thermostat.

The gauge does not read until the engine is hot. When the engine is at running temperature the gauge does not read consistently and in fact only reports accurately when the car s at idle in the garage after driving. Most of the time if if does read the temperature it is far below what my test gauge tells me the actual temperature is. I’ve tried at least four different senders, two gauges, two different connectors to the gauge itself, a test connection between the sender and the gauge...

All the electronics share a common ground as do the senders.

Any thoughts.

DR
 

Dodgydave

Joined Jun 22, 2012
9,954
What does the temperature sensor give out , a voltage or resistance to ground, and what does the guage reqire for full scale reading?
 

SamR

Joined Mar 19, 2019
3,411
There should be a system cooling water temp sensor installed already going to an idiot light. Simply replace it with the gauge sensor. Unless you're a belt and suspenders kind of guy... Engine temp sensors typically have an integral thermowell that inserts into the coolant flow so a tee is not feasible as would be for pressure. That gives them better readings at the point the engine makers thinks is the best place for the sensor. YMMV
 

Thread Starter

Danraabe

Joined Jan 3, 2021
11
Good question. The gauge responds to a change of resistance. I’m not sure what that means to the signal - the hotter it gets, the lower the resistance and the more voltage goes to ground...? I know the oil pressure responds to a change of resistance as well. Resistance decreases as the pressure goes up.
 

Thread Starter

Danraabe

Joined Jan 3, 2021
11
There should be a system cooling water temp sensor installed already going to an idiot light. Simply replace it with the gauge sensor. Unless you're a belt and suspenders kind of guy... Engine temp sensors typically have an integral thermowell that inserts into the coolant flow so a tee is not feasible as would be for pressure. That gives them better readings at the point the engine makers thinks is the best place for the sensor. YMMV
Thanks mate. NOt exactly sure what you just said but I think the threads are different on the senders. Also the temp signal on the thermostat goes through the computer so if not present it will create a fault and trigger the check engine light. The gauge sender goes directly to the gauge and is located in the top radiator hose. It screws into an aluminum connector I placed at the connection of two hoses.
 

LowQCab

Joined Nov 6, 2012
558
There is nothing wrong with your new Gauge, or its Sensor.

Other than the Cylinder-Head or Engine-Block Coolant-Passages,
the only reliable readings will be from your Coolant-Bypass-Hose(s).

This function allows the continuous circulation of Coolant throughout the Engine
regardless of the Thermostat being open or closed.
It keeps the Coolant at a constant, even, Temperature throughout the Engine.

You may not have a separate, dedicated, Coolant-Bypass-Hose.
The Coolant-Bypass-Hose Function may be integrated into the Heater-Hoses,
where a Bypass-Style-Heater-Valve
either recirculates Coolant directly back to the Water-Pump,
or sends it to the Heater-Core inside the Car first,
and then sends it back to the Pump.

You need to know which direction the Coolant flows in if you use the Heater Hoses,
you need the Hose that is coming from the Cylinder-Head,
not the Hose returning to the Water-Pump.
The Hose returning to the Water-Pump
will be colder in the Winter-Months when the Car's Heater is on.

Installing a solid Brass-Tee-Fitting in this Line,
with the appropriate adapters,
will give you a perfect location for your new Temp-Sensor.

If you are not familiar with the Hose Routing on your Engine you may have to
take it to a shop that works on Minis and tell them what you are attempting.
Buy them Lunch and your likely to get a friendlier attitude.
 

drc_567

Joined Dec 29, 2008
1,110
1621974801244.png

Is there sufficient working space to install the gauge sensor in the hot water radiator hose at the point where it exits the engine block? This may permit a more accurate reading of the actual engine temperature, especially during the warm-up period, when the thermostat is fully closed and the engine coolant is not yet circulating.
 
It’s sender is located in the coolant line with the hottest water traveling to the top of the radiator after the thermostat.
that;s probably the way it would expect to act. problem is between guage and "chair", a make on problem is between computer and chair.

There is the thermostat, it's closed, no water. The bottom of the radiator is a good spot. You don;t want it affected by air either,
You kind have water or engine block temperature. The sensor may be close to the water jacket on the block side.
 

crutschow

Joined Mar 14, 2008
27,229
View attachment 239607

Is there sufficient working space to install the gauge sensor in the hot water radiator hose at the point where it exits the engine block? This may permit a more accurate reading of the actual engine temperature, especially during the warm-up period, when the thermostat is fully closed and the engine coolant is not yet circulating.
That diagram appears to be in error.
The thermostat is located at the hottest water, which is at the hose going to the top of the radiator.

I agree with LQC.
The erratic temperature readings are because you have the sensor after the thermostat, so it only sees hot water after the thermostat opens.
 

narkeleptk

Joined Mar 11, 2019
524
Good question. The gauge responds to a change of resistance. I’m not sure what that means to the signal -
Usually its a 5V sense coming from the ecu that goes through the sensor (basically a variable resistor) and back to an ecu sensor ground or grounded near by. As the resistance rises this 5V sense gets lower, when the resistance lowers the voltage goes back up. The ecu uses this voltage reading (0-5V) to determine what value to display. I reckon an aftermarket gauge will work the same way but maybe off 12V supply.
 

Thread Starter

Danraabe

Joined Jan 3, 2021
11
That diagram appears to be in error.
The thermostat is located at the hottest water, which is at the hose going to the top of the radiator.

I agree with LQC.
The erratic temperature readings are because you have the sensor after the thermostat, so it only sees hot water after the thermostat opens.
Thanks for the reply. But when the engine is hot is when this all matters. If I turn on the heater it gets warm within a couple of minutes but the water to the radiator is still cool. I've been thinking of bleeding and refilling the whole system to be sure there is no way an air bubble is interfering. I have a vacuum bleeder.
 

LowQCab

Joined Nov 6, 2012
558
""But when the engine is hot is when this all matters""
With experience you will find that being able to "watch" the Thermostat "open"
is very important to analyzing exactly what may be going on with your Cooling System.
Only monitoring the Coolant-Temperature,
after the Thermostat starts to open, and
is then afterwards repeatedly cycling, open & shut,
is of very limited usefulness.

Check for missing Plastic-Panels that control
Air-Flow into, and out of, of the Engine Compartment.
These are quite often critical pieces.

An intermittent Electric-Cooling-Fan can drive you crazy.
The Fans are controlled by the ECU, and the Engine's Temp-Sensor,
and usually includes 1 or 2 Relays.

It is unlikely that you have Air-Bubbles in the Cooling-System on a modern Car,
although there may be exceptions to this general-rule,
a little time in the appropriate Mini Forums will quickly reveal whether or not
your Model has any problems with retaining "Air-Pockets",
and the recommended procedure for removing them.

Keeping your "Coolant-Recovery-Reservoir" filled to the "Full-when-Hot" Line
will generally purge all the Bubbles out within ~4 or ~5 Heat/Cool Cycles.

If you are having Cooling problems,
the first thing to determine is whether or not the "wrong" type of Coolant
has been mixed with the "Factory-Recommended-Coolant".

This is no trivial matter.
There are distinctly different Chemistries used in various different Coolant types,
and some of them, when mixed together, may create a nasty sludge which
can clog your Radiator COMPLETELY,
and it can never be completely removed except by disassembly and Steam-Cleaning,
or by parts replacement, or both.

Replace the Radiator-Pressure-Cap,
and the Engine's Coolant-Thermostat,
just to eliminate them from the problem equation.
They both should be replaced every ~2-years in any case.

If you position Your new Gauge-Temp-Sensor anywhere other than
the 2 places that I outlined previously,
you will be creating additional confusion where there should be none.
 
Thanks for the reply. But when the engine is hot is when this all matters. If I turn on the heater it gets warm within a couple of minutes but the water to the radiator is still cool. I've been thinking of bleeding and refilling the whole system to be sure there is no way an air bubble is interfering. I have a vacuum bleeder.
It is perfectly normal to have heat before the engine is up to temp. The coolant always circulates through the heater core. As others have mentioned the sensor is on the wrong side of the thermostat. It won't ever work right if coolant is not flowing over it. The fact that it works st idle means the thermostat only opens at idle... Actually a good thing for now. The air flowing through the engine bay is enough to keep it cool for now. In warmer weather you should notice it working morre often
 

LowQCab

Joined Nov 6, 2012
558
In many Cars, the Coolant does not circulate through the Heater-Core unless
heat is called for by the AC/Heat Controls in the Dash.
At this point we have no idea whether or not a Bypass-Valve-System
is used in this particular Make and Model of Car.
 

t_glover

Joined Mar 16, 2021
18
Most automotive thermostats have a small bleed hole to allow air to bypass this also allows a very small amount of coolant to circulate so the outlet hose to the radiator may not get near as hot as the engine until the thermostat opens. There has to be a bypass system in place for circulation when the thermostat is closed. Most vehicles use the heater circuit as a bypass and a vent door in the heater to control the temperature. If the vehicle uses a coolant shutoff valve to control heat from the heater then there will be a bypass line from the thermostat back to the coolant pump.

The hose that goes from the engine to the top of the rad is not always the connected to the thermostat. It can be the inlet to the water pump which will be lower in temperature. You may have the sensor installed in the wrong hose.

The temp sensor needs to be in the recirculating coolant in the engine or bypass system to report what the correct coolant temperature in the engine is.

The graphic in post 8 is incorrect as it shows coolant coming out of the radiator and entering the cooling system through the thermostat. Coolant always enters the coolant pump and exits at the thermostat.
 
In many Cars, the Coolant does not circulate through the Heater-Core unless
heat is called for by the AC/Heat Controls in the Dash.
At this point we have no idea whether or not a Bypass-Valve-System
is used in this particular Make and Model of Car.
That part of the equation is pretty much a useless point. The fact that there is heat while the radiator is cool and how that is possible is what I was eluding to. How the actual system works doesn't really matter.

Edit... now that I am home and not trying to read my phone I see you pretty much covered what I said in your previous posts.
 
Last edited:
The graphic in post 8 is incorrect as it shows coolant coming out of the radiator and entering the cooling system through the thermostat. Coolant always enters the coolant pump and exits at the thermostat.
That is incorrect. Some engines now have the thermostat on the inlet side of the water pump as it can control temperatures better that way. Chevy V8's have been that way for a number of years (saw it when I changed my dad's water pump for him). Detroit Diesel engine thermostats are on the inlet side of the water pump. I'm sure there are more, but that is what I have experienced so far.

Edit... Detroit Diesel = the DD series currently in production... not the older ones
 
Last edited:

t_glover

Joined Mar 16, 2021
18
geekoftheweek you are right. I did some internet searching and there are a few examples of the thermostat located on the inlet on the engine.

I went out and checked the thermostat location on my 2018 GMC pickup with a 5.3 V8 and my wife's Honda Civic both have the thermostat on the outlet.

The rad hoses are not a good location for a temp gauge.
 
Top