Fluctuations in temperature guage readings - Page 3 - Alfa Romeo Bulletin Board & Forums
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post #31 of 49 (permalink) Old 08-19-2015, 03:55 AM
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My temperature gauge must be from planet zircon because it swings slightly when swerving the car, even just a little. It's enough to notice if you're looking at it.
other people say the same thing. mine doesn't in any way and , apparently , there are lots that don't so either this is some car specific issue amongst a small group of people with the same problem or some fundamental design/execution issue unique to a certain series of cars which means it should be identifiable and repairable.
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post #32 of 49 (permalink) Old 08-19-2015, 08:58 AM
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Yep, for the record mine moves a bit too. Not sure why you find this concept so impossible, Steve, 'cause it obviously happens. If you'd worked in a lab and swung some Magnehelic gauges around you'd know you can make the needle move with g-forces.

Hell, I'm driving the Spider today, if I remember I'll take a look at the temperature gauge and try to quantify it.

Tom

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post #33 of 49 (permalink) Old 08-19-2015, 09:58 AM
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Yep, for the record mine moves a bit too. Not sure why you find this concept so impossible, Steve, 'cause it obviously happens. If you'd worked in a lab and swung some Magnehelic gauges around you'd know you can make the needle move with g-forces.

Hell, I'm driving the Spider today, if I remember I'll take a look at the temperature gauge and try to quantify it.

well... I did some lab work while I was in school and I know I can pick up my old analog volt meter and make it move but automotive instruments... even the cheapest ones are quite different in their internal construction , presumably to combat just this effect. I use the race cars as an example simply because even the earliest f1 cars and atlantic cars that I have driven as well as my gtp car that ran at lemans all had cheapo smiths electric gages and those cars would make more than a g in cornering loads in their sleep and those gages were rock stable. a spider is lucky to make 1/2 a g driven on the ragged edge and that's not even what we are talking about about... we are talking normal street driving and casual turning. do you really believe these instruments are the worst ever made by anyone ever and can't tolerate that ? and if they are ... why doesn't every ones do it ? or even ALL the instruments in the same car ? i'm sorry but it just doesn't pass the smell test.

every race car I built in the last 5 years of my career had electric instruments and all were equipped with multi channel data acquisition . the traces that they would pull up showed no drift or hysteresis as all and those gages were off the shelf autometer or stewart warner . nothing special or expensive. and ... like I said... mine exhibits no such phenomena

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post #34 of 49 (permalink) Old 08-19-2015, 10:26 AM
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Fact: Coolant Gauge Sender on the S3 2.0L is located on the intake manifold (right side of engine, near top), and we have to assume that this is sensing the temperature at the uppermost (or one of the highest) coolant passages in the engine.

OK. How about this theory (which bongju suggested in his initial post):

A. There is an air pocket in the system, and that's where it is trapped (since it's the highest point in the coolant system).
B. On right hand turns, centrifugal forces cause liquid coolant to press up against (and cover or submerge) the sender's tip.
C. On left hand turns, centrifugal forces cause the liquid coolant to move away from the sender's tip, exposing it to only the gas pocket in the system.

Would it be logical to expect the gauge to react that quickly to contact with the liquid or the gas? I would think so.

Would it also be logical to expect that the gas in the air pocket would be a noticeably lower temperature than the liquid coolant? I'm not too sure about that.

Either way, if turning the car causes the sender tip to be exposed to only liquid (or gas), would those two elements be at different enough temperatures to produce this anomaly on the gauge?

Does it only appear when an air pocket is present in the system, and that's why some cars exhibit it while other don't (because it's really hard to get all the air out of the system when refilling the coolant in these cars)?

Edward
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post #35 of 49 (permalink) Old 08-19-2015, 10:34 AM Thread Starter
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That's what I was thinking. However, I think your descriptions for B and C are reversed. On right hand turns, the coolant will slosh toward the left side of the engine exposing the sender tip to air. On left hand turns, the coolant would cover the tip.

Kim - 1987 Spider Quadrifoglio (~170K original owner miles)
Huntsville, AL
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post #36 of 49 (permalink) Old 08-19-2015, 10:51 AM
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That's what I was thinking. However, I think your descriptions for B and C are reversed. On right hand turns, the coolant will slosh toward the left side of the engine exposing the sender tip to air. On left hand turns, the coolant would cover the tip.
Ahhh. YES! I did get that reversed. Thanks for catching it.

And that would make the theory even more plausible, since the gas would clearly be at a higher temperature than the liquid, hence the higher gauge reading on right hand turns.

Edward
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post #37 of 49 (permalink) Old 08-19-2015, 12:04 PM
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Fact: Coolant Gauge Sender on the S3 2.0L is located on the intake manifold (right side of engine, near top), and we have to assume that this is sensing the temperature at the uppermost (or one of the highest) coolant passages in the engine.

OK. How about this theory (which bongju suggested in his initial post):

A. There is an air pocket in the system, and that's where it is trapped (since it's the highest point in the coolant system).
B. On right hand turns, centrifugal forces cause liquid coolant to press up against (and cover or submerge) the sender's tip.
C. On left hand turns, centrifugal forces cause the liquid coolant to move away from the sender's tip, exposing it to only the gas pocket in the system.

Would it be logical to expect the gauge to react that quickly to contact with the liquid or the gas? I would think so.

Would it also be logical to expect that the gas in the air pocket would be a noticeably lower temperature than the liquid coolant? I'm not too sure about that.

Either way, if turning the car causes the sender tip to be exposed to only liquid (or gas), would those two elements be at different enough temperatures to produce this anomaly on the gauge?

Does it only appear when an air pocket is present in the system, and that's why some cars exhibit it while other don't (because it's really hard to get all the air out of the system when refilling the coolant in these cars)?

exactly. that's why I was expecting the higher pressure new cap and a thorough bleed to have a meaningful effect and im surprised it didn't.

how about taking the sending unit out and cleaning the threads just to tick one more box ? or , while thinking about it , how about bad/loose connections on the back of the gage itself... those would be affected by movement if they were loose.
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post #38 of 49 (permalink) Old 08-19-2015, 12:10 PM
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exactly. that's why I was expecting the higher pressure new cap and a thorough bleed to have a meaningful effect and im surprised it didn't.

how about taking the sending unit out and cleaning the threads just to tick one more box ? or , while thinking about it , how about bad/loose connections on the back of the gage itself... those would be affected by movement if they were loose.
I concur. All good suggestions Steve.

Edward
'88 Quad - "Claudia"
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post #39 of 49 (permalink) Old 08-19-2015, 12:36 PM
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Guys, I just did the test on my '91 (same gauges as the S3). At operating temperature the temp gauge swings 20F low in left turns and 30F high in right turns from inertia. S4 cooling system is self bleeding so I guarantee there is no air in there.

This should not be a surprise: gauges are only designed to read accurately in a specific orientation. It'll vary with the gauge and damping, of course, but it's not abnormal for gauges to be a bit of a g-meter.

You don't have an actual temperature problem, Bongju: you're chasing an instrumentation issue. Drive the car and don't worry about it.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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post #40 of 49 (permalink) Old 08-19-2015, 01:28 PM
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Guys, I just did the test on my '91 (same gauges as the S3). At operating temperature the temp gauge swings 20F low in left turns and 30F high in right turns from inertia. S4 cooling system is self bleeding so I guarantee there is no air in there.

This should not be a surprise: gauges are only designed to read accurately in a specific orientation. It'll vary with the gauge and damping, of course, but it's not abnormal for gauges to be a bit of a g-meter.

You don't have an actual temperature problem, Bongju: you're chasing an instrumentation issue. Drive the car and don't worry about it.
do all your gages move in the same way ?
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post #41 of 49 (permalink) Old 08-19-2015, 01:30 PM
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I tested this on a thirty minute run today too, and mine moves ever so slightly in the direction of the turn. I'm also pretty sure my system is well bled. The needle is always rock solid at 175, and when I put my infrared thermometer on the top of the motor where the temp sender is it always reads 195, if I recall correctly.

Just another point of info...

Peter: 86 Spider since new; rebuilt motor after throwing a rod, rebuild tuned by Fred DiMatteo; formerly 82 Spider, 85 GTV6
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post #42 of 49 (permalink) Old 08-19-2015, 01:54 PM
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Here are some photos of an unmounted cluster in three different positions. You can clearly see that the needles for temperature and oil pressure are not balanced and the baseline position will vary with g-forces.

Note that the needle moves in the opposite direction of gravity, which means in a right turn the temp will go up and on a left turn it'll go down. Interestingly the temperature gauge moves the most and the volt gauge barely moves at all.

Again Bongju, you're chasing an instrumentation problem. Drive the car and don't worry about it.
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post #43 of 49 (permalink) Old 08-19-2015, 02:02 PM Thread Starter
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Wow, Tom. That's pretty good evidence for a centrifugal force effect. Thanks very much for taking the time to post these pictures.

Kim - 1987 Spider Quadrifoglio (~170K original owner miles)
Huntsville, AL
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post #44 of 49 (permalink) Old 08-19-2015, 03:18 PM
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Here are some photos of an unmounted cluster in three different positions. You can clearly see that the needles for temperature and oil pressure are not balanced and the baseline position will vary with g-forces.

Note that the needle moves in the opposite direction of gravity, which means in a right turn the temp will go up and on a left turn it'll go down. Interestingly the temperature gauge moves the most and the volt gauge barely moves at all.

Again Bongju, you're chasing an instrumentation problem. Drive the car and don't worry about it.
power them up and then do the same test and you will see a comprehensively different result. and you never said whether all your instruments move in the same manner as your temp gage ... which they should if your assertion is correct unless all your others have the special captain kirk inertial damping system that I understand was an option that year. look... you want to believe this nonsense that's up to you... but in another light , telling someone to ignore what his instruments say is simply the worst possible advice to give anyone at any time. there are plenty of intelligent ways to determine the issue other than " drive it and if it happens to roast then you will know the answer. "

and just by the way... whats your answer for having no movement before he changed the coolant and after he has the dreaded inertial effect ? reverse polarity on his flux capacitor when he got antifreeze on it ?

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post #45 of 49 (permalink) Old 08-19-2015, 03:48 PM
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power them up and then do the same test and you will see a comprehensively different result. and you never said whether all your instruments move in the same manner as your temp gage ... which they should if your assertion is correct unless all your others have the special captain kirk inertial damping system that I understand was an option that year.
Yeah, it'll behave a bit differently when powered, I'm sure. That doesn't change the fact that the needle isn't equally balanced around the pivot, so with constant magnetization of the coils (constant temp) you'll see some physical needle shift as the forces on the pointer change.

If you look at how the gauge works internally this should be fairly obvious. Most gauges are only designed to be accurate in one orientation.

Also, as you can see in the pic, the gauges are apparently balanced differently from each other. So I wouldn't expect them to behave exactly the same, no.

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look... you want to believe this nonsense that's up to you... but in another light , telling someone to ignore what his instruments say is simply the worst possible advice to give anyone at any time. there are plenty of intelligent ways to determine the issue other than " drive it and if it happens to roast then you will know the answer. "
Well, I said if he was really concerned to verify the temperatures with an IR thermometer. But given that the car is running well and not blowing coolant or anything there doesn't appear to be any real problem.

Again, my car has does exactly the same thing for twelve years. It's running great, not overheating at all even with the A/C on, and I know there's no air in the cooling system. So what would you suggest I do? Rip the whole thing apart looking for a non-existent problem? Replace the instrument cluster?

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and just by the way... whats your answer for having no movement before he changed the coolant and after he has the dreaded inertial effect ? reverse polarity on his flux capacitor when he got antifreeze on it ?
a) Dunno. Perhaps he wasn't looking for it at that time. I can tell you my car's done this for literally twelve years without change, though.

b) You're mixing your Trekkie, Planet Zircon, and Back to the Future references. That's poor form.

Seriously, I'm not sure why you want so badly for there to be a problem here. You're the only man I've met who actually trusts Alfa gauges...I mean, most of the time they're suggestions rather than rules.

Anyway, have you even TRIED this on your car? Like, really looking for it? If you have an S3/S4 cluster I'm pretty sure you'll see the needle move if you corner hard. And if you don't have an S3, how do you know what's normal so as to give advice to others?

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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