Engine Temperature Sensor

[docc]

The Sport developed unstable idle issues yesterday. It reminded me of how it acted before the Low Mass Sensor Modification.

 

Today, I discovered the connector had come unplugged. And also that the sensor holder was loose where it screws into the head. Tightened the holder back down, re-attached the connector and back to goodness!

 

While working up the modification, I had made the catches for the connector less prominent (more angled than squared off) to help getting the connector on and off. I'm thinking I took off too much material and when the holder loosened in the head, the vibration wiggled the connector off.

 

Hey, I know:  "I messed with it!" But after three years, and coping with some very high ambient temperatures, the sensor does still work better.

 

If it's connected.

[JBBenson]

I wanted to change mine and the plastic shredded while unscrewing. The copper piece left over was countersunk, rendering a 16mm socket useless, other than for rounding off the edges of the nut. I took half the bike apart to get to it.

 

After soaking overnight in PB Blaster, I ended up using this to get it out, after trying everything else.

 

Just a warning for those who think it is a 30 minute job. Uh.... no.

 

[Kiwi_Roy]

So after reading some of these posts and having the bike apart anyway for a shock rebuild I decided to take my temp sensor out to see what it looked like from the other end. The first thing I did was break the bake-o-lite holder. So now I'm kind of committed to doing something with it. So I took it apart ala Docc's project. Picture of parts below. But I have some questions.

1. Is the white paste of any significance IE do I need it?

2. Can I use the original bottom piece that screws into the head or do I need to modify it somehow?

3. What gap do I need between the top and bottom piece and how much tolorence do I have?

I have a lathe and some acetal rod which I think is similar to Docc's delrin.

The paste is called Heat Sink Compound, it's used on electronic components to conduct the heat away, if it's not touching something it wont do anything.

I think the idea is to run the thermistor a little cooler so it adds a little fuel, I wonder what the temperature difference ends up at?

 

The active part of the sensor is a thermistor worth about $1, I still have a few if you need one.

[GuzziMoto]

 

I think the idea is to run the thermistor a little cooler so it adds a little fuel, . . .

 

That was HatchetWackers original idea.

But using an air gap between the temp sensor and the engine (the source of the heat) will result in less heat being transferred to the temp sensor. So it will measure a lower temp.

And the idea that the small mass of the original sensor was slower to change temp than the much higher mass of the engine is also a bit suspect. But then Docc knows my thoughts on all this already.

I am not saying what they did can't make the engine run better, I am just saying it is not because it more accurately measure engine temp.

[Dan M]

Just a couple of thoughts on this touchy subject. The replacement sensor from GM if used is the same calibration as the MG unit. That was the primary reason it was chosen. If one uses the MG unit and strips away the brass, the accuracy does not change. So there is no cheating or fooling the computer as suggested. The whole reason the bare sensor or the GM air temp sensor work better is because they react very quickly. If you look in the original thread you will see they were compared side by side. The brass unit would get hot and stay hot minutes longer than the air temp sensor. Adding conductive paste made matters worse. Running in hot stop and go traffic it would not cool down and cause the ECU to miscalculate the fuel ratio.

The modified sensor does not make it run richer across the board. It merely adapts to engine temp faster. My fuel economy has actually improved. And, as Docc and others have said, hot weather, low throttle fueling is greatly improved.

[GuzziMoto]

Just a couple of thoughts on this touchy subject. The replacement sensor from GM if used is the same calibration as the MG unit. That was the primary reason it was chosen. If one uses the MG unit and strips away the brass, the accuracy does not change. So there is no cheating or fooling the computer as suggested. The whole reason the bare sensor or the GM air temp sensor work better is because they react very quickly. If you look in the original thread you will see they were compared side by side. The brass unit would get hot and stay hot minutes longer than the air temp sensor. Adding conductive paste made matters worse. Running in hot stop and go traffic it would not cool down and cause the ECU to miscalculate the fuel ratio.

The modified sensor does not make it run richer across the board. It merely adapts to engine temp faster. My fuel economy has actually improved. And, as Docc and others have said, hot weather, low throttle fueling is greatly improved.

I am sorry, but if you measure the temp of an engine (that is creating heat) with a direct contact sensor it will read the exact temp of whatever you are measuring. If you try to measure the temp of that engine but with a temp sensor that is measuring the temp of the air right next to the engine it will read a lower temp then the actual temp of the engine. It is not something that is optional. The air right next to the engine will be cooler than the engine when the engine is hotter than the ambient temp. The modified sensor might make the bike fuel better but it could not possibly measure the temp of the engine more accurately. The air gap between it and the engine acts as an insulator.

Sorry. It is a case of getting the desired result but not for the reason you think.

[luhbo]

This air insulated GM unit will never measure, or more precisely, indicate the head temperature better or quicker than the brass one does by one simple reason (as said above already): it's insulated from what it should measure. It's as easy as that.
This 10 gr brass unit, properly coupled to the 5 kg aluminium head with the help of some heat conductive stuff, is perfectly up to the task. An air gap is not what you want to have in this system.

 

Hubert

[GuzziMoto]

Air cooled engine temp varies greatly. Aluminum heads change temp pretty rapidly with airflow. A brass sensor that was designed to be submerged in coolant but was instead installed in a holder screwed into the head does not. The brass sensor as designed was never in direct contact with the head.

That is the whole point.

If you really think that that big chunk of aluminum called a Moto Guzzi engine can cool down faster than that tiny chunk of brass that is the sensor.....

Even if you forget the rest of the engine and just focus on the cylinder head vs. the brass temp sensor. The brass temp sensor is much less mass and will cool down faster than the head. And if the tiny brass sensor is physically attached to the aluminum head it will only ever heat up as hot as the head. It is not possible for it to get hotter than the head. It has no heat source other than the head, how could it get hotter than its heat source.

There were some serious assumptions being made in the original thread. The most obvious one is that if you improve the accuracy of the temp reading it would cause the motor to run better. I am not sure why that was being assumed, it seemed awfully naive. But, as there are more than a few widgets out there that can be used to generate a lower temp reading than what is in fact correct and that those widgets are then used to alter the way modern FI motorcycles run by tricking the ECU into adding a little more fuel with the intention of improving the fueling, it seems obvious that by insulating the engine temp sensor slightly from the cylinder head with a slight air gap it stands to reason that you would get a similar result. You would get a slightly lower engine temp reading, especially when the engine temp is at its hottest (the higher the engine temp the greater the effect the air gap would have, I believe), and the result of that is the ECU adds a little more fuel (or in some cases prevents the ECU from removing fuel as it may do if it senses the engine is too hot).

Again, to anyone who wants to take that route for fueling adjustment with their V11, fine. Have at it. But please don't try to tell me or anyone else that your air gap engine temp sensor is "more accurate" than the original engine temp sensor. It is simply reading slightly lower, and possibly the hotter the engine gets the greater the offset to the reading.

[Dan M]

One has to wonder why Moto Guzzi chose to insulate the brass sensor from the head with a plastic holder. Why didn't they screw the sensor directly into the head?

For whatever reason they did it as they did and mapped it accordingly. 

 

I would agree when starting from scratch and creating a map, a direct connection to measure cylinder head temp would be best. It certainly is in a liquid cooled engine. I still don't think I'd choose a brass sensor designed to be measure liquid temp on an air cooled engine. I've seen bad readings with these sensors screwed directly into automotive cylinder heads that were low on coolant. If the brass is not submerged it is very slow to react.

 

This mod is a very easy way to get improved fueling across the board without making major changes to the OE map. There have been many reports on this forum by those who chose to go with the direct connection of a brass sensor holder or the addition of paste with poor results.  I can not recall anyone who has used the air temp sensor approach and has not been pleased with the results. 

[GuzziMoto]

I have not heard anyone question the fact that it will do what it does. The debate seems to be that some people, the originator of the idea included, don't seem to understand how and why it achieves the adjustment to the fueling that it seems to bring.

[Kiwi_Roy]

What I do for a living is design measuring systems

 

I'm staying right out of this

[Kiwi_Roy]

Ok, if you want to measure temperature accurately you need to get the sensor in close contact, like right inside.

With it extended by a piece of plastic it will be quite a bit cooler than the engine because the heat is radiated by the extension and also air cooled, i'm sure you have heard of wind chill.

The air gap will probably not effect the reading but it will slow the response because air has a terrible heat transfer coefficient.

Reading a bit cooler might not be a bad thing, it should I think result in a slightly richer mixture.

 

http://www.physicsclassroom.com/class/thermalP/Lesson-1/Rates-of-Heat-Transfer