Temp gauge/sender wiring.

[nickdick]

Just bought a temp gauge for my Volvo MD7A. Can I just connect the sender wire from the new gauge to the existing sender AND keep the connection to the overheat light and buzzer on the control panel intact ? Wishful thinking I suppose.

 

[capeholm]

Nick, if the buzzer and overheat light are on an extra wire, you should be able to keep it connected. If you can scan in a copy of the electric circuit from the ships or ships`engine manual, I could tell you for sure.
Horst

 

[Haven't-a-Clue]

Just bought a temp gauge for my Volvo MD7A. Can I just connect the sender wire from the new gauge to the existing sender AND keep the connection to the overheat light and buzzer on the control panel intact ? Wishful thinking I suppose.

Just gone down this route but with a Beta BZ482. The overheat alarm sender on this has 2 terminals, so it was a simple case of connecting the sender wire 'twixt one and t'other. Bingo, now I knows that I can run all day at 2800 safely. If you've only got one terminal on the engine temp sender, it would be worth trying a 'piggy-back' type conecter, ie a single female with 2 male tabs. You can get 'em from Halfords. While suggesting this, I am, of course, assuming that the sender is of the resistance type etc.

 

[lenseman]

Just bought a temp gauge for my Volvo MD7A. Can I just connect the sender wire from the new gauge to the existing sender AND keep the connection to the overheat light and buzzer on the control panel intact ? Wishful thinking I suppose.

Most engine temperature guages work on the princliple on a small change in voltage through the device. This is obtained from the temprature 'sender', fitted to the engine, changing its resistance with a change in temperature.

The 'sender' unit is comprised of a NTC device, Negitave Temperature Coefficient Device (very rarely PTC Device, Positive Temperature Coefficient).

As the NTC device becomes warm and then hot, its internal resistance lowers towards zero ohms.

Now, this is the important part, these NTC devices usually have a plastic insulator and it is the colour of this insulator which gives a clue as to which type of NTC device you have fitted. Colours used are BLACK, RED, WHITE, BLUE and GREEN. They are all different.

Some 'sender' units have a code (number) stamped into one of the flanges on the brass hex flats where the spanner unscrews the device. If you are brutal and use pliers to remove the 'sender' unit, there is a possibility you might destroy the information (evidence) about which type of NTC device that is fitted!

Once fitted, if your new temperature guage reads incorrectly, you might be able to change the 'sender' unit to one which matches the volatge range required by the new temperature unit. Check with Volvo Marine.

I see no reason why you cannot retain the original wirring and alarm circuit which is extant.

If the temperature 'sender' wire that clips onto the 'sender' unit is grounded (touched onto the body of the engine), the temperature guage indication will slowly rise and read full scale (over heating) and return towards cold once the earth is removed from the 'sender' unit.

 

[VicS]

Just bought a temp gauge for my Volvo MD7A. Can I just connect the sender wire from the new gauge to the existing sender AND keep the connection to the overheat light and buzzer on the control panel intact ? Wishful thinking I suppose.

I would think the answer is almost ceratinly no. The temprature gauge will work on the principles outlined above, while the sensor for the existing warning light and alarm is almost certainly a temperature sensitive switch.

The wiring diagram in the owners manual, which can be downloaded from volvopenta.com shows only a warning light.

The wiring diagram in the workshop manual, which can be downloaded from bluemoment.com similarly shows only a warning light. Although the diagram for the later versions of the MD6A shows a gauge but no warning light


The parts breakdown at marinepartseurope.com shows two alternative sensors. Presumably one is the sensor for the gauge and the other for the warning light.

Unless there is provision on the engine to fit both sensors I think you may well have to choose between either a warning light ( and alarm) or just a temperature gauge.
If you can fit both sensors then that is the way forward.
Leave the existing warning light and alarm as it is, connected to their sensor via the main wiring harness. Connect the new temperature gauge via additional wiring to its sensor.

 

[starfire]

some of those with 2 terminals combine both the switch and sensor into one unit.

I maybe that there is a part to fit the volvos, or something from a car parts supplier ?