Need a location to install an aftermarket temp sender in 3.0

[chrisbalich]

Good morning friends and frenemies!

I've recently installed an ECU Master EMU Black on my SC. I installed a 993 CHT sensor above cylinder 4, but it's not the best solution for engine temp. My engine can be at full temp, but driving in a cold rain and the CHT will read low.

So I've purchased a Bosch oil temp sensor. (Bosch pn 0280130026) I intend to install this new sensor in the engine and to then use the oil temp as engine temp. The car is still NA, so I don't need it to react to rapidly changing oil temps. I need it to be stable and to actually let the EFI know when the engine is up to temp.

So my question is this.
Where on this engine should I mount the sensor?

I've been told the breather cover will work, but it won't be a stream/bath of oil. It'll just be inside the engine and exposed to oil vapor/spray. This would be my preferred location as it'll be the easiest to wire.
There's also the bank 1 chain case, but IDK if it'll get into the cam gear because of the length of the sensor. And it'll have the same problem with not being immersed in oil.

Any experience/insight will be greatly appreciated.

Pic for attention

[Jonny042]

I'm here to offer the opinion that you are better off getting the CHT to work. This is based on the potentially faulty notion that the 3.2 motronic used CHT, not oil temp.

I liked your solution but remember thinking it wasn't going to work but keeping my (possibly wrong) opinion to myself. Mostly because you'd already done a pretty excellent job with this and had it wrapped:



I don't know that you'll get the heat effect you need, by clamping onto the cooling fins, which might already be cool, plus there's a bunch of cooling air being blown right at the sensor and mount..... but adding some heat transfer compound might help the situation. Relocating it to a hotter spot might help.

Next, maybe a bit of tweaking of the correction tables or map or whatever is supposed to happen as the sensor heats up is in order? I mean, as long as you are getting some sort of signal out of the CHT you should be able to work with it?

[Jonny042]

Second thought...... you know me I'm all about light and cheap....

https://www.amazon.com/Thermocouple-Cylinder-Temperature-Washer-Sensor/dp/B07YZPGCG4

[chrisbalich]

Originally Posted by Jonny042

I'm here to offer the opinion that you are better off getting the CHT to work. This is based on the potentially faulty notion that the 3.2 motronic used CHT, not oil temp.

I liked your solution but remember thinking it wasn't going to work but keeping my (possibly wrong) opinion to myself. Mostly because you'd already done a pretty excellent job with this and had it wrapped:



I don't know that you'll get the heat effect you need, by clamping onto the cooling fins, which might already be cool, plus there's a bunch of cooling air being blown right at the sensor and mount..... but adding some heat transfer compound might help the situation. Relocating it to a hotter spot might help.

Next, maybe a bit of tweaking of the correction tables or map or whatever is supposed to happen as the sensor heats up is in order? I mean, as long as you are getting some sort of signal out of the CHT you should be able to work with it?

I looked at that picture and thought, "Dang, that looks really nice." About 2 minutes later, I went back and looked again and THEN realized it's my picture of my work. LOL
I can rework the tune to account for the lower temps shown at this point. I can also move the sensor and I have some thermal paste from some work laptop service a while back.
But it does swing pretty quickly when the car idles vs on the move. So I know the cooling fins are cooling.
I also considered building a small air dam around the CHT pickup point. My concern is that this may make a hot spot that actually puts the engine at risk.

Originally Posted by Jonny042

Second thought...... you know me I'm all about light and cheap....

https://www.amazon.com/Thermocouple-Cylinder-Temperature-Washer-Sensor/dp/B07YZPGCG4

I looked at these before I settled on the 993 CHT setup. I couldn't find a suitable place to mount it, so I passed. I'm not keen to make spark plug changes any more complicated than they already are, so it'd have to go on the engine somewhere.

[Jonny042]

Originally Posted by chrisbalich

But it does swing pretty quickly when the car idles vs on the move. So I know the cooling fins are cooling.

I think you'll have to accept that as a matter of course. Still it's probably possible to tweak the correction so it doesn't interfere with proper running, or even use that to your advantage to make it run better.

You might be able to turn on the auto tune and then when it comes up with a set of correction values, instead of dumping them into the VE map, apply them to the temp correction tables instead. I suppose you'll have to do that manually.

When do you plan to have the motor out again? I think the factory spot is pretty good on the 3.2 heads. I have a scrap 3.0SC head (loaned out at the moment) that I could poke at and see if it's practical to machine a spot for the sensor in-situ. Doubt it will be possible with the motor in though.

Or, you could try looking for oil temp

[chrisbalich]

Originally Posted by Jonny042

I think you'll have to accept that as a matter of course. Still it's probably possible to tweak the correction so it doesn't interfere with proper running, or even use that to your advantage to make it run better.

You might be able to turn on the auto tune and then when it comes up with a set of correction values, instead of dumping them into the VE map, apply them to the temp correction tables instead. I suppose you'll have to do that manually.

When do you plan to have the motor out again? I think the factory spot is pretty good on the 3.2 heads. I have a scrap 3.0SC head (loaned out at the moment) that I could poke at and see if it's practical to machine a spot for the sensor in-situ. Doubt it will be possible with the motor in though.

Or, you could try looking for oil temp

It'd be cool if the CHT had an EV1 connector instead of the Porsche-specific connector. Then, I could install the oil temp sender and switch back easily enough. Or use oil when it's cold and CHT when it's hot. (outside)

[tk32]

Disclaimer: I don't know anything, especially about 3.0. I looked pretty hard at a 2.7 once and stayed at a holiday inn express recently, thats about it.

[/QUOTE]

Is this large enough... or can you mod it to be large enough to fit:

- oil pressure sender for factory gauge
- oil temp sender for factory gauge
- oil sump drian plug (committed to the low lyfe, bad idea)
- oil tank drain plug?
- some other unused port with a plug in it right now? (also probably where the Bosch sensor would go...)
- some case bolt with not a lot of air flow over it cyl. 3 or 6?? ..

It'll probably leak like a sieve. Prefect, up-to-temp. oil leaking all over the sensor for accurate measurement!

Alternate option maybe the Bosch sensor can be adapted to be the oil tank drain plug, that'd be interesting.

OK I'm out/

[chrisbalich]

Originally Posted by tk32

Disclaimer: I don't know anything, especially about 3.0. I looked pretty hard at a 2.7 once and stayed at a holiday inn express recently, thats about it.



Is this large enough... or can you mod it to be large enough to fit:

- oil pressure sender for factory gauge
- oil temp sender for factory gauge
- oil sump drian plug (committed to the low lyfe, bad idea)
- oil tank drain plug?
- some other unused port with a plug in it right now? (also probably where the Bosch sensor would go...)
- some case bolt with not a lot of air flow over it cyl. 3 or 6?? ..

It'll probably leak like a sieve. Prefect, up-to-temp. oil leaking all over the sensor for accurate measurement!

Alternate option maybe the Bosch sensor can be adapted to be the oil tank drain plug, that'd be interesting.

OK I'm out/

I like where your head is at, but I think all of those options would leak oil and the Dude can't abide oil leaks.

I'm going to try tapping the breather cover and stabbing the Bosch sensor in it. The threads are the same chunk of brass as the probe, so I figure the breather case will provide engine temp even if it's not exactly oil temp. I should be able to tune around it pretty handily...as long as it holds temp.

[al lkosmal]

Chris,
I've been using these, mounted in the 1,2,3 side chain cover. It threads into the thermo-time switch port.



regards,
al

[spuggy]

My Motec conversion got a VDO sensor in the left chaincase (where the TTS used to be) for oil temp. This seems to correspond well to oil temp readings on the dash gauge - but I found it useless for warmup compensation as it took far too long to register temperature increase (think how slowly the oil temp gauge in the dash rises after starting to drive the car).

As a result, the motor was quite obviously getting warmup compensation trim for much longer after cold start than it actually needed.

I used the TurboKraft CHT kit, that adapts a 3.2 CHT to a plate that slides between the cooling fins on the rear cylinder on the left - #3 I believe, the one that has the scavenge pump on a 930 anyway. Which you'll need to remove to get the tin off, if you've got one. And re-index/reset, if you've got a cam sensor in yours. Sigh.

You modify the engine tin slightly (cut a slot to allow the plate to pass through), but this can be removed/refitted with the motor in the car. Although you'll likely curse your induction system and lack of quadruple-jointed forearms more than once in the process, as it's fiddly/obscured...

IIRC, there's a small chamber that the CHT sensor screws into; you fill this (most of the way) with oil (or AT fluid, I forget), so there's good thermal contact rather than air/splash to the sensor. You have to fit (eg "notch" and "file") the plate to allow it to slide between the fins (this might actually be due to the bottom plugs come to think of it). I used a liberal smear of a good quality (Arctic Silver) CPU thermal grease.

It works very well for me; I see CHT readings rising immediately after start, and I pull wamup compensation out by 60C - which is a few, like 2-3, minutes running time, tops. By which time the motor is running well without. My only concern is the high CHT numbers logged if you let the motor idle for 10 minutes or more, so I try not to do that...

[al lkosmal]

Both sensor locations are a trade off., but the ECUs provide you with the ability to taper off the enrichments, based on the temp from either approach....I remember having this conversation a while back....

Ingo provided this input, which sums it up best.

"In an air-cooled engine the cylinder head temperature (CHT) raises much faster than the temperature of the entire engine block. Megasquirt uses the temperature reading to calculate the enrichment during warm-up. A CHT sensor is not the best solution here to tell what is going on in the engine, especially if you use the washer-style thernocouples at the spark plugs. The 964 and later engines use a sensor mounted into the heads away from the plugs.

In general Megasquirt uses the engine temperature to calculate the warm-up enrichment. You can either use an oil temperature sensor or a cylinder head temperature sensor. In both cases Megasquirt allows you to calibrate the sensor response.

Fact is that the oil temperature goes up rather slow while the cylinder head temperature goes up much quicker during warm-up. Once you decide which way to go take readings of the "cold" engine and the temperature once the engine is all warmed up. Since Megasquirt allows you to modify the calibration curve that translates the temperature into an enrichment factor you can compensate for the sensor characteristics. In other words, if you use the CHT make it richen up the mixture until it is almost at operating temps. If you use the oil temperature, dial back enrichment as soon as you see the oil temperature raise across 140 degrees."

[Mahler9th]

For decades performance and racing engine builders I know have used a sensor in the breather cover for engine temp.

Dozens of engines.

My EFI system is a Haltech-- has been since 2001. Engine temp is picked up by an inexpensive GM-style engine temp sensor like this one:

https://www.haltech.com/product/ht-010304-coolant-temp-sensor/

I have a 3.6-based racing engine.

[chrisbalich]

Originally Posted by al lkosmal

Chris,
I've been using these, mounted in the 1,2,3 side chain cover. It threads into the thermo-time switch port.



regards,
al

Al,
Thanks!
Do you have any trouble with it getting good ground? I would guess with the chain cases being isolated with a gasket at the large opening and an o-ring at the cam, it'd be tough to get a decent signal out of it.
I can always buy/cut an adapter to thread in the sender I have to the chain case if it comes to that.

Originally Posted by spuggy

My Motec conversion got a VDO sensor in the left chaincase (where the TTS used to be) for oil temp. This seems to correspond well to oil temp readings on the dash gauge - but I found it useless for warmup compensation as it took far too long to register temperature increase (think how slowly the oil temp gauge in the dash rises after starting to drive the car).

As a result, the motor was quite obviously getting warmup compensation trim for much longer after cold start than it actually needed.

I used the TurboKraft CHT kit, that adapts a 3.2 CHT to a plate that slides between the cooling fins on the rear cylinder on the left - #3 I believe, the one that has the scavenge pump on a 930 anyway. Which you'll need to remove to get the tin off, if you've got one. And re-index/reset, if you've got a cam sensor in yours. Sigh.

You modify the engine tin slightly (cut a slot to allow the plate to pass through), but this can be removed/refitted with the motor in the car. Although you'll likely curse your induction system and lack of quadruple-jointed forearms more than once in the process, as it's fiddly/obscured...

IIRC, there's a small chamber that the CHT sensor screws into; you fill this (most of the way) with oil (or AT fluid, I forget), so there's good thermal contact rather than air/splash to the sensor. You have to fit (eg "notch" and "file") the plate to allow it to slide between the fins (this might actually be due to the bottom plugs come to think of it). I used a liberal smear of a good quality (Arctic Silver) CPU thermal grease.

It works very well for me; I see CHT readings rising immediately after start, and I pull wamup compensation out by 60C - which is a few, like 2-3, minutes running time, tops. By which time the motor is running well without. My only concern is the high CHT numbers logged if you let the motor idle for 10 minutes or more, so I try not to do that...

I do have a Clewett cam sensor at the back of cyl 3. I won't pay for that slick CHT adapter plate, but I may yet make one whenever the engine next comes out. I reckon it'd be really easy to make.
I have warmup finishing in that 50-60C range as well. But when it's 38*F ambient, it takes a while for the engine to get to 60C.
And with no proper heat, I have a tendency to let the car idle for long periods of time. So it needs to read [reasonably] accurately under all conditions.

[spuggy]

My EFI Ducatis all use an temperature sensor in the rocker cover, rather than a CHT per se. So I believe that's probably an acceptable approach, too. They knock out warmup compensation pretty fast. I think 60C is the magic number almost everyone seems to use. Works for me.

Which jibes pretty well with my experience of driving and riding cars/motorcycles with manual chokes for a few decades; you don't need choke for longer than a minute or 3, as soon as there was heat in the heads/valves - you're good... I would always would knock the choke off when pulling away, and just keep RPMs higher at the next couple of stop lights if necessary.

My $0.2; taking temperature reading from the wrong place gives you, well, inaccurate readings. You don't need the whole block to be completely up to temperature.

If you use the oil temperature, dial back enrichment as soon as you see the oil temperature raise across 140 degrees

IIRC, my chaincase sensor doesn't read 140 - in any temperature scale, Fahrenheit or Celsius - until the oil temp starts to rise off the bottom stop, which is some 10-15 minutes of running with a big FMOC. Perfectly usable as an axis on the boost control table (eg restrict to wastegate spring pressure only until oil is warmed), but didn't provide readings that made any sense for warmup compensation for me.

I mean, heck, I could hear the motor running too rich 4 miles from my house. Because the chaincase sensor wasn't reading over ambient yet. But it didn't need trim at all by then.

Your mileage may vary etc.

[al lkosmal]

Chris,
although the cam chain covers are gasketed, the bolted connections make for a good ground path to the case. Works well.
regards,
al

[chrisbalich]

Originally Posted by al lkosmal

Both sensor locations are a trade off., but the ECUs provide you with the ability to taper off the enrichments, based on the temp from either approach....I remember having this conversation a while back....

Ingo provided this input, which sums it up best.

"In an air-cooled engine the cylinder head temperature (CHT) raises much faster than the temperature of the entire engine block. Megasquirt uses the temperature reading to calculate the enrichment during warm-up. A CHT sensor is not the best solution here to tell what is going on in the engine, especially if you use the washer-style thernocouples at the spark plugs. The 964 and later engines use a sensor mounted into the heads away from the plugs.

In general Megasquirt uses the engine temperature to calculate the warm-up enrichment. You can either use an oil temperature sensor or a cylinder head temperature sensor. In both cases Megasquirt allows you to calibrate the sensor response.

Fact is that the oil temperature goes up rather slow while the cylinder head temperature goes up much quicker during warm-up. Once you decide which way to go take readings of the "cold" engine and the temperature once the engine is all warmed up. Since Megasquirt allows you to modify the calibration curve that translates the temperature into an enrichment factor you can compensate for the sensor characteristics. In other words, if you use the CHT make it richen up the mixture until it is almost at operating temps. If you use the oil temperature, dial back enrichment as soon as you see the oil temperature raise across 140 degrees."

This closely parallels my MS3X experience as well. I've made some adjustments to the warmup curve already. I'll dial in the curve once I get temp readings I'm happy with.

Originally Posted by Mahler9th

For decades performance and racing engine builders I know have used a sensor in the breather cover for engine temp.

Dozens of engines.

My EFI system is a Haltech-- has been since 2001. Engine temp is picked up by an inexpensive GM-style engine temp sensor like this one:

https://www.haltech.com/product/ht-010304-coolant-temp-sensor/

I have a 3.6-based racing engine.

Sounds good to me. This is what I plan to try once I get the breather back off the car and change the Porsche connector for an EV1.

Originally Posted by spuggy

My EFI Ducatis all use an temperature sensor in the rocker cover, rather than a CHT per se. So I believe that's probably an acceptable approach, too. They knock out warmup compensation pretty fast. I think 60C is the magic number almost everyone seems to use. Works for me.

Which jibes pretty well with my experience of driving and riding cars/motorcycles with manual chokes for a few decades; you don't need choke for longer than a minute or 3, as soon as there was heat in the heads/valves - you're good... I would always would knock the choke off when pulling away, and just keep RPMs higher at the next couple of stop lights if necessary.

My $0.2; taking temperature reading from the wrong place gives you, well, inaccurate readings. You don't need the whole block to be completely up to temperature.



IIRC, my chaincase sensor doesn't read 140 - in any temperature scale, Fahrenheit or Celsius - until the oil temp starts to rise off the bottom stop, which is some 10-15 minutes of running with a big FMOC. Perfectly usable as an axis on the boost control table (eg restrict to wastegate spring pressure only until oil is warmed), but didn't provide readings that made any sense for warmup compensation for me.

I mean, heck, I could hear the motor running too rich 4 miles from my house. Because the chaincase sensor wasn't reading over ambient yet. But it didn't need trim at all by then.

Your mileage may vary etc.

Yeah, I don't think I need a full 140*F. I reckon by 100-110*F it'll be plenty warm to run well. (flipping back and forth from F to C is good fun. )

Originally Posted by al lkosmal

Chris,
although the cam chain covers are gasketed, the bolted connections make for a good ground path to the case. Works well.
regards,
al

Good to know.
Thanks, Al!

[spuggy]

Originally Posted by chrisbalich

I do have a Clewett cam sensor at the back of cyl 3. I won't pay for that slick CHT adapter plate, but I may yet make one whenever the engine next comes out. I reckon it'd be really easy to make.

I think it'd certainly be easier to make/fit one with the motor out, LOL...

Originally Posted by chrisbalich

I have warmup finishing in that 50-60C range as well. But when it's 38*F ambient, it takes a while for the engine to get to 60C.

Yes, a little while.

I've got several trial cold starts inter-mixed in the most recent log I pulled up to look at; but starting from a ~10C ambient and IAT, ECU, CHT and oil temp within 3 degrees of each other:

CHT hits 20C within ~30 seconds of starting, (chaincase) oil temp has come up 2 degrees.

30C on CHT, chaincase temp has come up 0.5C.

40C on CHT, chaincase reads 12C

50C on CHT, chaincase reads 13.7C

60C on CHT, chaincase reads 15.8C

Each 10C rise in CHT temp is roughly 1 minute apart (darn the Motec I2C log reader, which makes this hard to figure - there's gotta be a trick for that).

70C on CHT, chaincase reads 16.6C

Some 6-7 minutes elapsed; heater in lambda sensor reached temperature, and providing readings.

80C on CHT, chaincase reads 18.7C

90C on CHT, chaincase reads 25.8C. Which could actually be ambient inside the engine bay, as the Motec reports 22.3C. IAT (intercooler outlet) reads 12.6C

Head temps over 90C depend on load - just cruising around with light throttle won't increase them. I don't see much more than 100C or so when the car is moving.

10 minutes elapsed; chaincase reads 40C

17 minutes elapsed; chaincase reads 50C

20 minutes elapsed; chaincase reads 60C

Stop for gas; on re-start, chaincase sensor has heat soaked to 78.9C (highest reading) and IAT picks up another 5C (to 20C).

One issue I see with using chaincase sensor for warmup compensation; I logged 60C CHT when the chaincase was reading 16C/60F - you could have ambient exceeding that in summer.

Originally Posted by chrisbalich

And with no proper heat, I have a tendency to let the car idle for long periods of time. So it needs to read [reasonably] accurately under all conditions.

Pretty sure it does. I never leave any motor I care about - especially an air-cooled one - just idling for long - especially from cold - but that's just me.

I think few appreciate just how hot the heads get with inadequate airflow when idling - when messing with idle trim, injector timing etc, I saw 250C on the CHT after 10-15 minutes or so. Now I set a temp alarm of 180C on the Motec dash. Which, for perspective, is almost twice as hot as the car runs under boost.

Which most likely doesn't actually hurt them; it's been SOP at most shops to leave them idling to get the oil hot for changes for many, many, years, right?

[chrisbalich]

Yep. Lots of places just let them idle to heat up the oil.
I don't have heater ducts so all of the fan-blown air is passing right by the engine.

And as I'm still shaking bugs out of my tune, it idles ~1100. So it moves a bit more air than idling at 900.

Thanks for the data points. That's a big help.

As my own data point, with the CHT sensor where I've placed it, I've never seen CHT temps above 75C. Not with idling, beating on it, or highway cruising.

[spuggy]

Originally Posted by chrisbalich

it idles ~1100. So it moves a bit more air than idling at 900.

930 has a bigger fan than the 3.0, I believe? My high CHTs when idling were recorded in high ambients; as relatively ineffective as my heat exchangers are at 14F, the flappers would most certainly be closed at 80+F...

I've always set the idle to 1050 when hot. It seems much happier there with SC cams.

Originally Posted by chrisbalich

Thanks for the data points. That's a big help.

You're welcome!

Originally Posted by chrisbalich

As my own data point, with the CHT sensor where I've placed it, I've never seen CHT temps above 75C. Not with idling, beating on it, or highway cruising.

That does seem odd.

Perhaps double-check the calibration for the sensor? Despite both being NTC thermistors, the Magneti Marelli and Bosch sensors have very different curves. To the point that I deemed them non-interchangeable (and markedly so <100C) when trying to avoid a 400% markup over the generic...

I believe all Bosch NTC sensors are the same composition/provide the same curve, certainly all the ones I've compared the datasheets for are.. I'd also strongly suspect the 993 sensor would be Bosch

As Jonny suggested, some thermal paste between the fins/sensor - and maybe a few drops of oil/AT fluid in the housing - to improve thermal connectivity?

[chrisbalich]

Originally Posted by spuggy

930 has a bigger fan than the 3.0, I believe? My high CHTs when idling were recorded in high ambients; as relatively ineffective as my heat exchangers are at 14F, the flappers would most certainly be closed at 80+F...
All of my datum has been harvested in cold/cool ambients. 34*F-65*F
IDK about the size of the fan. I do know that there are different pulley ratios for different submodels of 911.

I've always set the idle to 1050 when hot. It seems much happier there with SC cams.
Yeah, I want to get the idle down to 900. It'll take me a little bit to figure out how the IACV programming works on top of getting the warmup strategy dialed in.


You're welcome!



That does seem odd.

Perhaps double-check the calibration for the sensor? Despite both being NTC thermistors, the Magneti Marelli and Bosch sensors have very different curves. To the point that I deemed them non-interchangeable (and markedly so <100C) when trying to avoid a 400% markup over the generic...
I do intend to confirm the calibration curves for all the sensors.

I believe all Bosch NTC sensors are the same composition/provide the same curve, certainly all the ones I've compared the datasheets for are.. I'd also strongly suspect the 993 sensor would be Bosch

As Jonny suggested, some thermal paste between the fins/sensor - and maybe a few drops of oil/AT fluid in the housing - to improve thermal connectivity?

I need to make a new CHT sensor adapter. There's a pinhole in the bottom of the adapter, so any fluid will run out and all over the engine. That tiny cavity of air could be affecting my readings, but I doubt by too much. **But I'm not that kind of doctor, so it's entirely possible I've underestimated the effect of that small air gap.


Kelly is going out tonight, so I plan to spend some quality time in the garage when I get home from work. I'm going to pull the breather cover, drill & tap it, install the sensor, and pull the CHT sensor & adapter. I'll see if Ethan can buzz closed the tiny pinhole in it tomorrow. I'll have to make some decisions about whether or not to make any wiring changes.