Engine monitor instruments

[Monsta]

I have been considering this digital instrument Digital Engine, Gearbox & EGT temp 52mm gauge visual/audible overheating alarm | eBay.

It monitors EGT, engine and gearbox temperatures. The EGT sensor is a conventional probe inserted in the exhaust gas stream, but the engine and gearbox sensors are the external bolt-on type that measure the temperature of the external surface of the casing rather than the temperature of the actual coolant or automatic transmission fluid.

Measuring the temperature of the external casing is unlikely to be as accurate, but I'd like to know whether it still gives a reasonably accurate measure ?

 

[Old.Tony]

It won't respond as quickly to internal changes, and will be affected by external influences (like driving through water). But it will give you one indication that the coolant temp sensor won't: engine temperature when there's no coolant left in the radiator. And maybe that's got some value, so you might find its usefulness anyway!

 

[OldManBeard]

Before buying that unit I'd suggest you contact them and ask how the sensors are installed. Are they simply attached to the outside of the case or do you need to drill and tap holes to screw them into? The latter is not something I'd want to do in situ, as it is extremely likely to leave metal particles inside the case.

 

[Monsta]

The temperature sensors are bolted to the outside of the case using an existing stud.
I'd like to know whether anyone has used bolt-on sensors like this and how they found their performance.

 

[Horatius]

The temperature sensors are bolted to the outside of the case using an existing stud.
I'd like to know whether anyone has used bolt-on sensors like this and how they found their performance.

Yes, I use this type of thermocouple bolted to the head for my "engine watchdog" unit. They're excellent. I kept the normal gauge with coolant sensor in the top hose for a while as well, to compare them. They were generally within 1 degree or so of each other, though the bolt on unit was much faster reacting to temperature changes as you would expect.

As old Tony mentioned, the great value of these bolt on ones is that if you suffer a sudden loss of coolant they will alert you to temperature change straight away. Whereas a coolant sensor won't as it needs to be immersed in coolant to give a correct reading. In fact it's common for coolant sensors to show the engine temperature initially dropping with a loss of coolant and by the time it indicates overheating it's too late.

I think they would generally be good for auto transmissions, haven't used one for that but have heard of people using and being happy with them for keeping check of transmission temps.

 

[Monsta]

Tony and Horatius, many thanks for your replies.

Yes, I use this type of thermocouple bolted to the head for my "engine watchdog" unit. They're excellent. I kept the normal gauge with coolant sensor in the top hose for a while as well, to compare them. They were generally within 1 degree or so of each other, though the bolt on unit was much faster reacting to temperature changes as you would expect.

Horatius, that is exactly the confirmation I was looking for - a close correlation between the temperature as measured by the bolt-on and the 'normal' sensor.

As old Tony mentioned, the great value of these bolt on ones is that if you suffer a sudden loss of coolant they will alert you to temperature change straight away. Whereas a coolant sensor won't as it needs to be immersed in coolant to give a correct reading. In fact it's common for coolant sensors to show the engine temperature initially dropping with a loss of coolant and by the time it indicates overheating it's too late.

I get the direct water temp reading from OBD2, but the bolt-on sensor presents an added bonus.

I have a 2011 auto D40, so I presume that the bolt-on sensor on the transmission casing would have a similarly close correlation to the automatic transmission fluid temperature. I can not get transmission temperature from my OBD2, so this and EGT are the main readings I am wanting in a gauge.

This particular gauge I am considering has all three, with the ability to set custom alarms, both visual and audible. In normal range the icons are green. Once a reading goes beyond normal the icon changes to orange. When it hits the pre-set maximum it changes to red and sounds an alarm.