engine oil temp sensor

[Skeeve]

There are a few things here that are clear. The bikes were spec'd with a plastic holder. The plastic holder insulates the sensor from the head. Altering that head to sensor connection will change what the computer sees. Making a better physical connection between the sensor and the head will give a higher temp reading to the computer. A higher temp reading will lean the mixture.

[Emphasis added]

 

Up to a point; obviously, the map should take into account that above a certain temp reading, it should be increasing fuel [for cooling.] If it doesn't, the map needs work [which brings us back to Ratchet's contention, that messing w/ the probe will require a map update to prevent said mucking about from screwing up the already screwy stock map... ]

 

It seems clear to me that we need:

 

1] Faster feedback - this is achieved by eliminating the airspace w/ anti-seize, thermal paste, whatever [as long as it can survive the heat and do the job.]

 

2] Thermal isolation of the sensor body from the rest of the cylinder head - this is what is offered by the factory plastic receptacle.

 

3] Ruggedness of whatever part satisfies 1&2 above - this is where the stock plastic receptacle fails.

 

The only polymer option that I'm familiar with that would have the necessary hardness to take tools for insertion while being able to withstand long exposure to high heats is phenolic [bakelite.] Maybe something reinforced with a polyamide [Kevlar, Nomex?] would take the strain w/o failing when attempting to remove the sensor [on whatever maintenance schedule is deemed necessary.]

 

Obviously, making a bespoke run of such an esoteric material would be extraordinarily expensive, which is why Guzzi ended up w/ the plastic part they did. I don't even know if my proposed solution above would work any better than the stock part; I'm no materials science engineer! Making a finned aluminum part to hold & shield the sensor, with a Teflon sleeve to insulate the body of the sensor from the cylinder head might work, but Teflon melts at 327C (620F), so that might not work either [i don't know how hot the head gets in hard use. I'd think not hot enough at the point the sensor screws in to hit that temp extreme, but I'd want to test it w/ a laser thermometer first just to keep from getting any rude surprises... How [i]does[/i] one get melted teflon goo off their motor? ]

 

Anyway, those are my thoughts on this topic. Feel free to shoot them full of holes, so we can come up w/ an optimum solution.

[Guest ratchethack]

It seems clear to me that we need:

 

1] Faster feedback - this is achieved by eliminating the airspace w/ anti-seize, thermal paste, whatever [as long as it can survive the heat and do the job.]

 

2] Thermal isolation of the sensor body from the rest of the cylinder head - this is what is offered by the factory plastic receptacle.

I've been inclined in this direction lately myself, Skeeve.

 

UPDATE: My latest excursion with the plastic holder (after abortive multiple variable zero to ~6 mm air gap passes with the brass holder, and plastic holder with thermo paste) was with the plastic holder and a ~.075" air gap, no thermo-goop, and a 1.5" OD fender washer acting as a heat sink between the sensor and the holder. The fender washer heats up enough that I can't begin to touch it after the motor is up to operating temp, which tells me there's enough heat flow into the BODY of the sensor so that the fender washer is acting as a significant heat sink, more rapidly dumping heat off the sensor body than without. The relatively rapid removal of heat seems to have had a positive effect -- ergo, faster feedback.

 

Multiple longer-range, full operating temp rides lately confirm the above as the BEST YET combination with my "off the shelf" PC III map.

 

Now that I'm on the "faster feedback via rapid heat removal from sensor body" track, your 1-2 punch combo above is wot I've been noodling lately, Skeeve.

 

Next "test mule" -- plastic holder with 1.5" heat sink disk and ~.075" gap, filled with thermo-compound.

 

Will advise (Part VI).

[Dan M]

Are you sure the addition of a washer is not slowing things? It is more metal to heat and cool. It would be interesting to know how much faster or slower the voltage on the signal wire changes with or without your heat sink. Seems hard to make direct comparisons. You can back probe with a voltmeter and get a feel for how fast (and how much) the numbers change.

 

Still, the biggest missing piece of the puzzle is how much pulsewidth compensation is made at what temperatures.

[Dan M]

Up to a point; obviously, the map should take into account that above a certain temp reading, it should be increasing fuel [for cooling.] If it doesn't, the map needs work [which brings us back to Ratchet's contention, that messing w/ the probe will require a map update to prevent said mucking about from screwing up the already screwy stock map... ]

 

True, albeit a rather high temp. I've noticed most of my trouble above 80F and in slow traffic with low throttle openings. The additional cooling of wind or lower ambient temps or the added air / fuel of an open throttle covers a lot of evils. Like I said in my last post, It would be nice to know when and how much compensation is made.

[Guest ratchethack]

Are you sure the addition of a washer is not slowing things? It is more metal to heat and cool. It would be interesting to know how much faster or slower the voltage on the signal wire changes with or without your heat sink.

I'm not sure of anything but wot I've directly observed about the way it runs after the relatively "convenient" things I've tried, Dan. Of that, I have no doubts wotsoever. This is trial 'n error of the most unscientific nature, based on convenience, limited resources, interest level (not all that high, relatively speaking, since it runs so magnificently without me mucking with it a-tall) and time available, weather permitting.

 

On Saturday, we had heavy rain, snow, hail, significant flooding (within a few miles of me), and multiple water spouts off the coast. . .

Seems hard to make direct comparisons. You can back probe with a voltmeter and get a feel for how fast (and how much) the numbers change.

Aye. But the prospect of monitoring my DMM with hook probes on the sensor on the fly over considerable distances over hill and dale -- the ONLY chance of duplicating all the many modes of full temp operation that this needs to be tested under -- seem prohibitive to Yours Truly, not to mention subject to high error probabilities. . .

Still, the biggest missing piece of the puzzle is how much pulsewidth compensation is made at what temperatures.

This is just me, but I'd sooner leave this kind of analysis behavior to those (there's at least one I know of hereabouts) who've been known to log more hours on his TueneBoy and posting about it here by a factor of ~10x1 than he does riding his Guzzi. . . but leave me not slag those with obsessive tendencies, lest I slag meself in the process, eh?

 

Thanks for the input. Good food f'er thought.

[Greg Field]

There are a few things here that are clear. The bikes were spec'd with a plastic holder. The plastic holder insulates the sensor from the head. Altering that head to sensor connection will change what the computer sees. Making a better physical connection between the sensor and the head will give a higher temp reading to the computer. A higher temp reading will lean the mixture.

 

 

Well, I haven't talked to Wittner yet but will. In the meantime, let me argue the case that you all have it backasswards. Here goes:

 

Break open your stock sensor. What is the small metal bit made of? It looks like copper to me. What does copper do really well? It transfers heat really, really well. It's also expensive. It would never be speced unless the spec-er wnated maximum heat transfer, for cost reasons. Then, after spec-ing expensive copper, what do they make the rest of the holder out of? Plastic. What does plastic do pretty well? Many things, but among them is that it is a poor conductor of heat. So, they encase a great conductor of heat, which is screwed directly into the heat source and then encase the conductor in an insulator. Why would someone do that? Let's see if your mental faculties are firing tonight . . .

[gstallons]

I give up................why?

[Guzzi2Go]

Well, I haven't talked to Wittner yet but will. In the meantime, let me argue the case that you all have it backasswards. Here goes:

 

Break open your stock sensor. What is the small metal bit made of? It looks like copper to me. What does copper do really well? It transfers heat really, really well. It's also expensive. It would never be speced unless the spec-er wnated maximum heat transfer, for cost reasons. Then, after spec-ing expensive copper, what do they make the rest of the holder out of? Plastic. What does plastic do pretty well? Many things, but among them is that it is a poor conductor of heat. So, they encase a great conductor of heat, which is screwed directly into the heat source and then encase the conductor in an insulator. Why would someone do that? Let's see if your mental faculties are firing tonight . . .

I'd just like to add...

 

The spec-er drilled a hole in cylinder, filled it with air, took the coppery part, burried its tip 20mm bellow surface, and fastened everything with a nice, massive 19-wrench screw the the topmost cooler fin. What this thing actually measures is temperature of the cylinder head surface, not cylinder head (or oil temp, as per manual) itself. Never trust a spec-er (engineer)!

 

However, I agree with ratchet's statement here that the engine is tuned to honor this setup. On the other hand, the setup is far more ambient temperature dependent than it should be. If its colder, the engine will be running rich, hotter, probably does not matter (? - see bellow for explanation). If there is such thing as poor engineering on a Guzzi, than this is a blatant example of it. One way to address the issue of poor setup baseline without remapping (with all side effects that usually come from fumbling with vehicle electrics) could be to add a potentiometer in series to the NTC and to offset the entire map in the "direction of colder" (higher resistance) AND to fill the hole with thermal paste.

 

Reasoning

The sensor has a very non-linear (logarithmic) characteristics, and it's accuracy is not something to write home about (5%). To me that sound that at higher temperatures it is not used at all, and its primary (and most likely only) (am I now being parenthetical, or just pathetic-al? ) purpose is to serve as a choke button - cold - on/hot - off. To corroborate my claims I am quoting Jefferies My ECU tables being posted here: http://www.cajinnovations.com/MyECU/technical_site_map.html

 

There it says:

# TempR gives the value in ohms of the NTC temperature sensor
#Temp C   -30   -20   -10     0    10    20    25    30    40    50    60    70    80    90   100   110   125
TempR   51466 28618 16571  9712  5956  3742  2991  2408  1597  1077   746   524   375   274   203   152   102
# Crank is the % boost of the map injection times right after start
# this boost decays to 0 over about 20s
#Temp C   -30   -20   -10     0    10    20    25    30    40    50    60    70    80    90   100   110   125
Crank      80    70    65    60    60    60    55    50    35    25    20    15    15    15    15     0
# OilT is the permanent choking boost
#Temp C   -30   -20   -10     0    10    20    25    30    40    50    60    70    80    90   100   110   125
OilT%   +64.1 +53.1 +43.8 +35.2 +29.7 +18.8 +10.2  +9.4  +5.5  +0.0

TempR line maps temperature to the NTC's resistance. Observe the difference between 20-30°C and the one between 110-125°C. Not the sharpest tool at >100°C

 

Crank line is for cranking/choke. This one is valid for 20s. Observe that it is mapped up to 110°C in case someone wants to claim that head temp will never go over 70°C

 

OilT line is the interesting one. It says that if the measured temperature is >40°C, there is no influence whatsoever on the map.

 

Usual disclaimer: I reserve the right to be wrong on any or all accounts here listed, and would be glad to read an educated explanation on where did I go wrong in my line of thinking.

[tmcafe]

Just after Luigi made the sensor tip out of copper (perhaps according to Dr John's well though-out specs), he realized that he was going to run out of Lire and decided that plastico was going to save costs? Kind of like encasing an expensive gem in some cheap alloy cause you can't afford gold anymore? The shop manual otoh mentions that the case is plastic. Maybe they wanted to protect the sensor from outside temp, so that the tip would only pick up what's inside the cyl head? Bakelite would have prolly worked better. But surely the sensor was intended to pick up as much of the temp, and iirc Pete R saw some bikes that had come from factory with grease packed around sensor.

Somehow i suspect it's Luigi who ran out of "soldi" rather than a piece of crumbling crap with a high end purpose.

[Greg Field]

Here's what I would guess the purpose is:

 

The copper transfers the heat to the sensor tip. The plastic holder helps prevent too much heat from being sucked away from that copper tip.

 

This is also why I recommend using something to insulate the brass holders: keep the heat to the sensor.

 

Certainly, I could be the one who has it backasswards, but based on many bikes I've set up thyis way that run perfectly, I believe it to be the designer's intent. I will find out, though. I promise to get to that NLA Monday.

[Guzzi2Go]

Sensor is all metal. It is electrical connector part which is plastic.

 

Plastic washer + some other form of temp. insulation for the thread is a step in right direction. But this will make ECU believe the engine is hotter then it really is

[Greg Field]

The sensor holder is plastic, insulating all but the tip from the heat.

 

 

See how the copper base is insulated by the plastic and how the plastic extends upward to insulate as much as possible of the sensor? The copper base has, from memory, a little well milled into it that fits the tip of the sensor. These things indicate to me "intelligent design" intended to let the tip get an accurate read of head temp through contact between tip of sensor and the copper base. I may be wrong, though. I'll find out from the source and accurately report what he says.

[dlaing]

The sensor holder is plastic, insulating all but the tip from the heat.

 

img]http://i81.photobucket.com/albums/j221/greguzzi/PICT0001-1.jpg[/img

 

See how the copper base is insulated by the plastic and how the plastic extends upward to insulate as much as possible of the sensor? The copper base has, from memory, a little well milled into it that fits the tip of the sensor. These things indicate to me "intelligent design" intended to let the tip get an accurate read of head temp through contact between tip of sensor and the copper base. I may be wrong, though. I'll find out from the source and accurately report what he says.

Measuring at the tip will give a truer reading of the temperature in the engine, and the insulation will reduce the effect of weather throwing off the temperature at the sensor.

Seems intelligent to me, and I have not seen anyone prove there is a cheap FIAT cross ref part.

I am going to go back to wadding up teflon tape on the sensor thread to insulate against the brass holder.

Or maybe the part to replace my broken plastic piece will get her after 2 years or so of back order.

[Guzzi2Go]

The sensor holder is plastic, insulating all but the tip from the heat.

...

 

Ok then, what did I jizz into?

 

Any thoughts on "it will run to lean if thermal paste is added"?

 

Mind you, local woodoo priest says it does, scientist apprentice says it should not.

[Guest ratchethack]

# TempR gives the value in ohms of the NTC temperature sensor
#Temp C   -30   -20   -10     0    10    20    25    30    40    50    60    70    80    90   100   110   125
TempR   51466 28618 16571  9712  5956  3742  2991  2408  1597  1077   746   524   375   274   203   152   102
# Crank is the % boost of the map injection times right after start
# this boost decays to 0 over about 20s
#Temp C   -30   -20   -10     0    10    20    25    30    40    50    60    70    80    90   100   110   125
Crank      80    70    65    60    60    60    55    50    35    25    20    15    15    15    15     0
# OilT is the permanent choking boost
#Temp C   -30   -20   -10     0    10    20    25    30    40    50    60    70    80    90   100   110   125
OilT%   +64.1 +53.1 +43.8 +35.2 +29.7 +18.8 +10.2  +9.4  +5.5  +0.0

This data set is key, G2G. Thanks for posting. It puts some real perspective on things here.

 

Essentially, the OilT "choking boost" line says that as long as the part of the EXTERIOR of the head where the holder is seated (REMINDER: this is not the INTERIOR OF THE HEAD) is below body temp, the sensor will be boosting the pulsewidth and A/F by bumping up the map, and there's NO BOOST to the A/F above that temp.

 

The Crank boost decays to 0 at ~20 seconds, so once the EXTERIOR of the head is above body temp, and it's been running >20 sec., this says we may ignore both the OilT and Crank lines and focus exclusively on the TempR line.

 

On the TempR line, I'm focused on wot's happening between 40°C to 125°C, which is a progressive drop in resistance over half again greater than an order of magnitude. This appears to be the only relevant data to consider here once the motor is warmed up to operating temp and running. It's at the high temp end of this range where I've consistently observed the undesirable low-RPM driveability anomalies (apparent over-lean condition) caused by adding thermal paste for a direct thermal connection between holder base and sensor tip using the plastic holder.

Any thoughts on "it will run to lean if thermal paste is added"?

Back in May of '07 Tony Rolo thought this:

It now occurs to me that perhaps the sensor actually NEEDS to be at least partially insulated & that the CHT temp information provided by a properly installed & functioning sensor is what the ECU has been calibrated to. By placing the sensor in direct thermal contact with the head, temp data may be significantly elevated & therefore adversely affect the fuel map at various points. . .

Again, I b'lieve wot I've posted previously from my recent direct comparison observations points to exactly this. Again -- I cannot say that this will be the case for any but MY MAP and MY MOTOR ONLY, which has an "off the shelf" PC III map, when adding thermal paste to fill the OE ~.015" air gap in the plastic holder. I make NO ASSERTIONS wotsoever that an over-lean condition is necessarily wot's going on with someone else's motor and map when thermo-paste is added -- but I DO SUGGEST there might be a fairly reasonable probability that my situation isn't all that unique.

 

NOTE: Without much question, according to Greg and others, it seems clear that other maps on other bikes can, will, and DO vary considerably in this regard WRT what results in a "too lean" condition.

 

While we're waiting for comment from Dr. John, I wonder wot comments Cliff Jeffries might be inclined to t'row on this here little clusterfest/conflagration??

 

Enquiring minds. . . (well, you know). . .