Question: Temp gauge accuracy and proof..

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Grandpacorvair
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Question: Temp gauge accuracy and proof..

Post by Grandpacorvair »

Re: 1964 Spyder temperature gauge..

My gauge seems to read high...I know they aren't particularly accurate and I do use it as a reference only but I'm curious if I can find out how accurate it really is....(or isn't ;) )

I'm going to create a graph of the varistors resistance throughout the engines operating range (if the weather ever cooperates) However I need a way to check the gauge too. I am thinking about using a laser meter like Harbor Freight sells but where should I try to point it to get the best indication of true head temperature? As a test I tried to point it at the head through the left 'door' but it was almost impossible to avoid the influence of the exhaust log too.

To give you an idea of my gauge's operation, on a really hot day (90° plus) at highway speeds around 70mph, after a while the gauge will read around 500° or so. (GM says 575° triggers the overheat alarm) There is NO evidence of the engine running hot, no spark knock and pulling over and checking the engine it really doesn't seem like it's running that hot...

Also thinking about installing an oil temperature gauge to give an idea as to what's going on, but I have no idea what the 'normal' high oil temp is for a Turbo engine so that wouldn't necessarily answer the question of is the engine running too hot...


Any suggestions appreciated...
Kerry Borgne
1963 Spyder Convertible
Birmingham, Michigan
cnicol
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Re: Question: Temp gauge accuracy and proof..

Post by cnicol »

400-425F is about "normal" for a Turbo during highway use. Oil temp should be in the 220F range. I'm not sure when it was phased-in by there was a TSB published in "Service News" that added an inline resistor for Sypder temp gauges to lower the reading in vehicles erroneously indicating abnormally high temperature. Have you tried a different thermistor?
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'66 Rear Alum V8 4-dr
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66vairguy
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Re: Question: Temp gauge accuracy and proof..

Post by 66vairguy »

A few folks have "characterized" the gauges - they don't publish specifics since they use the data to develop modern drivers they want to sell - understandable.

What has been stated is the Spyder (EM) and Corsa (LM) gauges used the same thermistor, BUT the Spyder gauge had accuracy limitations and were prone to "drifting" or changing in response to changes in system voltages. The Corsa gauges were made differently and are less prone to system voltage fluctuations and are claimed to be more accurate.

The gauge faces are small and not detailed for accuracy. The thermistor response does change with age, but slowly.

Bottom line - do what most do. Figure out were the needle is during normal driving and while under load and if it goes above the "normal" it's time to pull over and check things out. The BEST overheating indicator is actually the generator/fan warning lamp as once the fan belt comes off the engine will overheat rapidly if you continue to operate it.

I've had vehicles with oil temperature gauges - nice in trucks, but useless in most cars since the oil is usually the LAST item to get hot when an engine overheats. Oil temperature gauges are mainly for powerplants that operate near maximum power for long periods like trucks and piston airplanes.

Finally at one of the conventions someone asked a GM presenter (possibly engineer Benzinger) why the specs. showed the turbo under WOT (wide open throttle) would overheat since the cooling system could not handle the heat at WOT on a turbo (fine on normally aspirated engines). The reply was something like - It would take about a minute of constant operation at WOT to overheat the engine and of course well before a minute you'd be at the maximum speed of the vehicle and that would be illegal (and unsafe) on a public road. Valid argument.
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Grandpacorvair
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Re: Question: Temp gauge accuracy and proof..

Post by Grandpacorvair »

cnicol wrote: Thu May 25, 2017 6:53 am 400-425F is about "normal" for a Turbo during highway use. Oil temp should be in the 220F range. I'm not sure when it was phased-in by there was a TSB published in "Service News" that added an inline resistor for Sypder temp gauges to lower the reading in vehicles erroneously indicating abnormally high temperature. Have you tried a different thermistor?
No, thermisters are generally made of unobtainium, or at least very expensive...
Kerry Borgne
1963 Spyder Convertible
Birmingham, Michigan
spyderman64
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Re: Question: Temp gauge accuracy and proof..

Post by spyderman64 »

Have you done the normal things to reduce/accommodate engine temps like deflashing the cylinder head fins, removing lower shrouds, and using synthetic oil? Some swear by a deeper oil pan also.
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bbodie52
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Re: Question: Temp gauge accuracy and proof..

Post by bbodie52 »

A deeper oil pan, as mentioned above, does essentially nothing to reduce oil temperature. It just creates a larger oil sump to hold more hot oil, but does little to add more radiating surface to dissipate the heat from the oil.

On the other hand, a specially designed oil pan that provides more heat transfer surface, such as the cast aluminum OTTO PARTS oil pan, adds more aluminum heat transfer surfaces via a series of aluminum posts and other raised aluminum sections on the inside surface and a large quantity of cooling fins on the outside surface. These additional posts and raised areas inside the pan provide more contact surface with the oil, to transfer heat to the aluminum pan. The additional cooling fins outside the pan help to transfer heat, in turn, from the aluminum oil pan to the air. The black finish, as opposed to a polished finish, also helps to promote heat transfer.

The use of synthetic oil does not necessarily promote better heat transfer from the engine, but it does have a higher tolerance for engine heat without the heat having a negative effect on the lubricating properties and other protective properties of the synthetic oil. It is particularly good for use with the turbocharger because of its high resistance to oil coking, which can form deposits on turbocharger bearing surfaces (especially during the heat surge that may occur in the turbocharger housing immediately after shutting down the engine).

For more information on Oil Coking, see the following...

:google: :search: :link: https://www.google.com/#q=oil+coking

:link: http://www.corvair.com/user-cgi/catalog ... graygo.y=0
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Brad Bodie
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lostboy
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Re: Question: Temp gauge accuracy and proof..

Post by lostboy »

bbodie52 wrote:A deeper oil pan, as mentioned above, does essentially nothing to reduce oil temperature. It just creates a larger oil sump to hold more hot oil, but does little to add more radiating surface to dissipate the heat from the oil.

On the other hand, a specially designed oil pan that provides more heat transfer surface, such as the cast aluminum OTTO PARTS oil pan, adds more aluminum heat transfer surfaces via a series of aluminum posts and other raised aluminum sections on the inside surface and a large quantity of cooling fins on the outside surface. These additional posts and raised areas inside the pan provide more contact surface with the oil, to transfer heat to the aluminum pan. The additional cooling fins outside the pan help to transfer heat, in turn, from the aluminum oil pan to the air. The black finish, as opposed to a polished finish, also helps to promote heat transfer.

The use of synthetic oil does not necessarily promote better heat transfer from the engine, but it does have a higher tolerance for engine heat without the heat having a negative effect on the lubricating properties and other protective properties of the synthetic oil. It is particularly good for use with the turbocharger because of its high resistance to oil coking, which can form deposits on turbocharger bearing surfaces (especially during the heat surge that may occur in the turbocharger housing immediately after shutting down the engine).

For more information on Oil Coking, see the following...

:google: :search: :link: https://www.google.com/#q=oil+coking

:link: http://www.corvair.com/user-cgi/catalog ... graygo.y=0
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How do the different aluminum pans compare? Like the Otto vs the clarks ultimate?


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1961 Corvair 700 Sedan (80hp 3spd Gasoline Heat)
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bbodie52
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Re: Question: Temp gauge accuracy and proof..

Post by bbodie52 »

Assuming similar quality control in the production of the two oil pans, and that both oil pans offer the benefits of a rigid aluminum casting over the standard steel stamping of the factory oil pan, Clark's promotes their oil pan as having greatly increased surface area in both the internal and external surfaces. That would appear to make the Clark's Corvair pan capable of transferring more heat than the Otto Parts oil pan (which was originally developed in the late 1960s or early 1970s).

:link: http://www.corvair.com/user-cgi/catalog ... IN&page=29
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The Clark's Corvair Parts oil pan lists for $254.05.
Image

The OTTO Parts oil pan lists for $225.35, or $231.10 with polished fin edges.


:link: http://www.corvair.com/user-cgi/catalog ... IN&page=30
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:link: http://www.corvair.com/user-cgi/catalog ... IN&page=31
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Brad Bodie
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Re: Question: Temp gauge accuracy and proof..

Post by 66vairguy »

Unless you are going racing the the Corvair oil cooling is not an issue - assuming you have a clean functioning stock oil cooler.

Oil lubricated turbo's do tend to have an issue with oil "coking" at the bearing. A common practice is to let the engine idle for a few minutes after a good run to cool the turbo housing. Some manufacturers even put in electric pumps to run oil through the bearing for a few minutes after shut down. The synthetic oils are more resistant to coking at the turbo bearing.

The deep oil pans look pretty, but tend to hit the road going up a driveway, especially if the rear springs are old. Most I've seen installed have impact marks on them.
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Danny Joe
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Re: Question: Temp gauge accuracy and proof..

Post by Danny Joe »

Your gauge may be accurate.

My car was running 500 or higher when cruising at 70 also. I deflashed the heads, made sure the compartment seals were all good, tried removing the lower shrouds for the summer, none of that had any effect on the temperature.

I was having some carburetor issues during this time (sometimes hard to start when hot, severe hesitation when coming off idle.) Rebuilt the carburetor, went through it again several times checking settings. Finally got a copy of Bob Helt's book on the YH, it was very helpful. My big problem turned out to be a poor seal on the float bowl cover. If air is leaking there, the proper vacuum cannot be maintained in that chamber. Lack of vacuum prevents the accelerator pump from working at low RPMs, causing hesitation. It also causes a very lean air/fuel ratio.

Now my temperatures run 350 or so around town, and 400 cruising at 75 on the interstate in 80+ degree weather!
Also leaks at the hose on the crossover and the throttle plate adapter can contribute to a lean condition.
My gas mileage went down, but it's running nice and cool now.
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Re: Question: Temp gauge accuracy and proof..

Post by bbodie52 »

:goodpost: I fully concur that the average highway temperature on the Corsa cylinder head temperature gauge seems to always be straight up, at 400° while continuously running at highway speeds. I remember in particular a cross-country run from Atlanta to Los Angeles in the middle of summer 1983. We are driving a 1965 Corvair Corsa coupe with a 140 hp 4×1 engine. The car was fully loaded with a family of four and all of our luggage. We drove the full distance from Atlanta to Los Angeles in three days — driving during daylight hours. The temperatures in particular in Arizona and Southern California through the desert area were quite hot! I remember stopping in Needles California to make a phone call, and found that the payphone handset was so hot that I could not hold it in my bare hand. The heat was getting to my family in our non-air-conditioned Corvair, but did not seem to be bothering the engine that all. The cylinder head temperature gauge never registered above 400°. Even after stopping for breaks I never had any trouble with vapor lock or any condition that prevented the engine from immediately restarting upon demand. Total distance was 2410 miles of daylight driving in August with a fully loaded Corvair — NO PROBLEMS! :tu: :tongue:
Brad Bodie
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Re: Question: Temp gauge accuracy and proof..

Post by 66vairguy »

For "normal" operation the Corvair cooling system is adequate. GM did testing at their summer proving grounds in 100+ temperatures to ensure it worked. It was documented that the turbo at WOT would exceed the Corvair cooling ability, but only after about a minute - longer than anyone would operate it at WOT for street driving and legal speeds. A Motor Trend test of a 1965 Turbo Corsa stated the car reached 79 MPH in 18.1 seconds in a 1/4 mile. Another magazine (noted for abusing test cars) obtained 78 MPH in 15.6 seconds in a 1/4 mile.
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Grandpacorvair
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Re: Question: Temp gauge accuracy and proof..

Post by Grandpacorvair »

So, I finally got around to testing the gauge against the chart. While my 'tests' showed some discrepancies they weren't where they I wanted them to be!

At the bottom end of the range my gauge read a little high, at the midpoint it was 100° high however the next step reversed the error and the gauge read low! By the time I got to 500 ohms the gauge tracked the chart spot on.... I was hoping it would be reading high... oh well there is still the thermistor to be 'tested' and rather than doing that, I think I will await the new 'incarnation' that is coming along soon...
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Kerry Borgne
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Re: Question: Temp gauge accuracy and proof..

Post by 66vairguy »

Forget the chart, it's not valid for testing gauges. It's only valid for testing thermistors with a passive multimeter while you are heating the thermistor. If you try to make the gauge response fit the chart it will NOT be accurate.

The gauges have a different response made to fit the thermistor when it is in NORMAL operation - that is conducting amperage from the gauge.
You can read up on thermistor "self heating responses". GM actually spec'd the thermistor resistance at a specific amperage.

Several have characterized the gauges in an attempt to make a new electronic driver. At the other forum one is in pre-production testing and should go on sale in June). The gauge data is NOT published because a lot of time was put into characterizing the gauges and those involved are running a business.

I have NO knowledge about this inventor or the product, but you can read about it at http://corvaircenter.com/phorum/read.ph ... 867,page=1
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