My Boxster is my daily driver and it's the only vehicle I have owned since 2013. I know this car like the back of my hand. I can feel when something is out of order. That being said, as noted the previous temp was between 185° to 186° (these temps are under normal driver conditions. Spirited driving would raise the temp more or sitting still for a long period the temp would go up), even in the Winter time and it's been this way as long as I have owned this car. I have experienced every variation you noted in the last week, except for the temp gauge inaccuracy other then Porsche's calibration, which I understand the gauge always reads lower then the actual temp and I don't have inaccuracy/inconsistency of visually sighting the temp gauge needle with over 6 years of ownership with the car being my DD and the only vehicle I have owned in over 6 years. The only thing different in the last week than previous weeks is the change of spark plugs and we are now in warmer weather.

It's been a week now since the plugs have been changed. I have done city driving short runs, highway driving for over an hour. I have experienced every situation in the last week, air temp changes, was very humid yesterday as it rained and went to 71° with Sunshine. Actually turned on the home A/C unit because of it. I have the four stalk column with the OBC turned on, so I can see the outside temps. I've always been puzzled why this car would still run as warm in the Winter time as it does.

I'm 51 and I have owned a very wide range of vehicles, all of them except one were fuel injected. I understand the ECU can advance and retard timing and adjust the fuel flow, however, the ECU can not control how quick the spark plug will fire over another plug, electricity follows the path of least resistance, the ECU can not control that and the intensity of spark you will get out of the spark plug do to the materials the spark plug is made out of and can not be changed by the ECU. No, even with today's computer controlled cars, you can't just stick any old spark plug into the engine and expect the engine to operate exactly the same. That's a very stupid statement.

My car ran great with the Bosch plugs and the car still runs great with the NGK plugs. The one thing I am seeing is the temp difference, while not huge, it's a pleasant surprise to see the lower temp. I watch my car like a hawk and I notice everything, even a slight change in the temp gauge needle position.

Hey there, friend: you can call me stupid all ya like.... but YOU are the one making a fool of yourself here.

The ecu doesn't HAVE to control "the intensity", as you call it. All the ecu has to do is measure (with the o2 sensor) how close to stoichiometry the burn is, and then adjust from there, as necessary.

You're sure arguing a lot, for a guy who doesn't understand the subject matter.

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What would be those variables? Were those variables not existant before the plug swap? You're suggesting that absent any other anecdotal evidence (of which there is none... he changed his plugs, nothing else) that the ~4 degrees spontaneously happened and had absolutely zero to do with it?

I'm interested in your response, and anyone else who suggests a placebo is in effect. I'd like this to make sense for me. Thank you.

Yes. Continue.

Why? Because you've already discounted the several I gave you? Or the dozen or so offered by another astute poster?

To me, if there is in fact a temp difference (I'm not sold on the accuracy of the factory needle) it's just as likely caused by the plug- installer bumping the temp sensor while he was down there.

Add mentioned below: there is ZERO science to support the postulation. You said below that you think he laid out science; he didn't. That's pure conjecture. Guessing. There's nothing there that holds water.

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Exactly and it wasn't just on one certain day. It's been every drive since the plug change.

Hey there buddy, I didn't call you stupid, I said your statement was very stupid and it was.

If the ECU isn't getting a proper/full burn reading from the O2 sensors the ECU may attempt to fix the issue with a air to fuel ratio adjustment, however there is only so much the ECU is going to step in on this as the ECU will override the O2 readings with the Mass Air Flow Meter readings and decide to give you a code for a bad cat(s). What do you guess my ECU is thinking about my O2 sensor readings, when I have 200 cell cats in my headers and no secondary cats (although the secondary cats have no O2 sensor after them)? Oh and when I put the new headers on, I also put all new Bosch O2 sensors on the car. The proper O2 sensors, not those kits where you splice in a new O2 sensor. Apparently the cat efficiency isn't bad enough to throw a CEL, but my Durametric will tell me the cat efficiency is below normal. However I did clear all codes from the car yesterday to see if I'm still getting the cat below efficiency warning again. Did you read the part of my post where I said my car eats a lot of gas? Actually, she is quiet a pig when it comes to fuel. The ECU is not attempting to cut the fuel on my car, which is a good thing for this engine as running them lean will kill them quickly, especially with the intake mods I have made, the car gets a lot more air in the intake now.

since you are being so aggressive about this, its time to call you out for a distinct lack of knowledge.

1. In closed loop, the car is reading the MAF voltage as well as the 02 sensor voltage, as well as half a dozen other sensors to determine how to maintain a stoich a/f ratio.

2. The 02 sensors that are used for A/F adjustment are PRE-CAT. The efficiency of your cats has nothing to do with the a/f.

3. If your ecu has to adjust a/f beyond typically 25%, you will receive lean/rich codes. Again, cat efficiency does not apply.

4. If your car is running rich, then you have some problem, potentially related to your maf sampling tube if you just stuffed in a 987 airbox.

You seem to have basically no clue how modern fuel injection operates, so I'd probably tone down the condescending commentary.

I've got it! I've got a scenario whereby changing the spark plugs can lower the coolant temp!

Work with me here:

When you jacked up the rear of the car to gain access to the motor, the little peice of cardboard that was partially blocking one of your radiators, fell into a different position, which is no longer blocking airflow.

I think this is MUCH more plausible than what you've been postulating.

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There is no such thing as a lean code on these cars, where did you come up with that one? You will need special equipment and sensors at a tune shop with a dyno to determine your AFR and adjust the ECU accordingly.

You can get tunes for these cars that ignore O2 sensors readings to the point where you can remove your O2 sensors from the car completely. Most guys that race their Boxters will put on headers and run without cats, block off the O2 ports (if any) in the exhaust and tie down the O2 sensor to an area of the car to keep it out of the way. Street guys that don't want to have a nagging CEL from the O2 sensor removal will get the tune to ignore the O2 sensors.

I never said my car was running rich, I said it eats a lot of gas. There is zero issue with my intake system setup that would cause the MAF not to read the air flow properly. My intake system still has the original MAF housing and the correct MAF for the diameter of the MAF housing. I know a lot about how the modern fuel injection system works on the Boxster, I've been studying it since December 2014, before I made any changes to my intake, to make sure I did everything properly.

Sorry to burst your bubble on this one, but yesterday I pulled the front bumper to do the annual rad clearing ritual. It was actually very clean. The passenger side had no debris in it and the driver's side had one leaf and a cigarette butt in it.

What the hell are you talking about. A simple wideband 02 in the exhaust can tell you your a/f ratio with excellent accuracy. Tunes can be done with obd flash tools if you see fit, but are hardly worth it for mostly stock cars. What that has to do with the price of tea in china, i'm not sure.

You realize, I hope, that these cars have FOUR 02 sensors. The front, i.e. pre-cat, 02 sensors are the ones that report the a/f ratio. Removing these is asinine and would remove an important element of how the car runs at part throttle. I'm 100% sure that racers remove their REAR 02 sensors, but again, that has nothing to do with a/f, so who cares about those.

My car is basically identical in its intake setup to yours, but mine has a 996 intake manifold, and my car gets excellent gas mileage so it seems you have an issue.

P1128/1130 are lean codes....so.....

Please stop, you just make yourself look silly.

Great thread!

The commentary is vibrant and, for the most part, polite. I'm just a shade-tree mechanic... but have learned from this forum, and seasoned posters, a plethora of information. Every single day, literally, I learn something new about the 986. That said...

Notwithstanding any variables... none... zero... assuming new plugs went in... no sensors were touched... car was raised and lowered without any jarring... basic plug change...

From where did that ~5 degrees come? If it wasn't there 5 minutes before the plug change... but surfaced 5 minutes after a plug change... wouldn't it be prudent to assume there existed a connection (absent "science") between the plug change and ~5 degrees?

Absent "scientific" explanations... what is the general concensus?

Thank you.

What the hell are you talking about? Now that I mentioned the special sensors, which the wideband 02 sensor is what I was referring to and our cars do not have these. So you will need to take the car to a tune shop to get your AFR adjusted properly for a lean or rich condition. Unless you have one heck of a nice home setup and you know what you're doing.

Tunes that remove O2 readings is what has to do with the price of tea in China. In other words, you saying O2 sensors are a must for a proper AFR is incorrect. A tuner can set the ECU to ignore the O2 sensors and actually make the these cars more responsive for street driving.

Do you not read anything I post? I stated I replaced all of my O2 sensors with new proper Bosch O2 sensors. So yes I know these cars have four O2 sensors and I also understand the roll they play in with ECU for streetability driving without a tune. Do you know why I have NHP 200 Cell Exhaust Headers? Because I have a Tiptronic car and these are the only headers that can be used with a Tiptronic car and retain the all four O2 sensors and have cats in the system to allow the ECU to read them properly.

When I say the car is a pig on gas, I mean when I'm putting the hammer down. In a 0 to 60 run the OBC will read out a .3 MPG drop and that's in 5.20 seconds, so imaging a full session of spirited driving. I've seen the OBC read out 16 MPG during spirited driving. On the norm city driving it's at 19 MPG on the highway it's at 24 MPG. Also the Tiptronic has a different gear ratio then the manuals.

1st gear 3.66 : 1
2nd gear 2.00 : 1
3rd gear 1.41 : 1
4th gear 1.00 : 1
5th gear 0.74 :1
Final drive ratio 3.73 : 1

Correct and I'm not saying this would be the case with every car in the entire world either. However it does appear the plug change did make a difference with my setup. It's not stock for sure and those Bosch plugs are decent, but not the greatest either. I'm happy with the results.

1. You made it sound as if dramatic and specialized equipment is needed for a/f ratio analysis. A wideband 02 kit with gauge is $160.

2. wow. so 02 sensors are just useless and removing makes the car run better? Thats news to me and to every single automobile produced within the last 25 years.

Lets examine that. So you have a tune that removes your 02 sensors. The 02s are what creates the bloody feedback loop. Without them, the computer will have no idea whether its changes are working to keep the a/f stoich. This is vital to closed loop driving, which makes continuous changes (have a look at your short term fuel trims) to fuel delivery and timing. Most cars as they age have slightly positive long term fuel trims meaning that the computer has to add fuel to keep the a/f stoich as fuel pumps age, injectors clog, vacuum leaks appear, etc. If you remove the 02 sensors, the computer would have no way of knowing about this. To remove front 02 sensors is absolutely horrible idea and is exactly why every car made in the past 25 years uses them.

Now, lets say you have a specific race car that only runs at WOT. Now, you may be able to tune fuel and timing maps with enough specificity at every temperature that the car would run ok without 02 sensors, but you'd be going by feel instead of data and would basically be reverting back to an electronic version of a carburetor. Any changes in barometric pressure, air density, etc would have to be tuned for, and that basically invalidates the whole point of electronic fuel injection in the first place.

As to your point about gas mileage at WOT....uh yeah, usually its not good.

Please do some reading on the topic before making these ludicrous statements.

this may help anyone whose confused...ahem

WHAT THE HOME MECHANIC NEEDS TO KNOW ABOUT O2 SENSORS

I'm not the least bit confused, thus the reason I bought the headers I have. To retain the O2 sensors and have a cats in the system to help on polluting the air, plus they are needed to pass inspection. I didn't pay $1,200 for a set of headers because I like to waste money.

https://i.postimg.cc/L5q3rhm9/headers.jpg

:cool:

yes you are, because you are talking about how tuners delete primary front 02 sensors to make the car "more responsive", which is total bs.

Can't admit you were wrong, huh?

Coincidence...………………..

Well I, for one, am glad for this. Because otherwise this is a very short and boring thread. :cheers:

I get a chuckle out of it though, when people are so afraid of learning something they didn't know before, that they'll double-down on their own fallacy. Even to the point of embarrassment. :o

I'm wrong. The front O2 sensors do have to stay. Yes I can admit when I'm wrong.

Cool, no biggie.

Now as to your coolant temps, i cant offer any explanation why plugs would cause this temp decrease.