A question about cylindar head temperature

[frez]

Hi everyone
In reading posts and manuals I see that Chevy likes the engine compartment to be at an ambient temp of 200 degrees, but if my thermistor is/was functioning correctly what should the temp read out be optimally. Is that also 200 I don't see that officially noted anywhere. On the same lens if I use the thermo reader to get a temp on the engine head I am assuming that is what should match the gauge, is that correct?
Thanks

[miniman82]

Depends on many factors, such as the gas you put it, how the timing is set up, the state of tune of the rest of the engine, what temperature it is outside, and how you drive it.

For what it's worth, the stock head temp gauge on Corsas so equipped is not an accurate device by any means. It's there so you can track trends, so if the needle does something it normally wouldn't then it's a clue to a possible problem. My 180 would run 350~425, depending on what outside temps were and how hard I was driving it. I always use pump premium fuel, and when it's above 70* outside the lower shrouds come off. 140's are probably a little more forgiving than a turbo engine, but I like to see it at 400 or below. When it's cold outside you kind of get what you get, I went one winter in Chicago where the head temp gauge never moved above 200 it was so cold.

[jmikulec]

I was just wandering how does one actually install these gauges on the engine. Do I just take the wire off the dummy light wire and put the new gauge wire on them.

[cad-kid]

I was just wandering how does one actually install these gauges on the engine. Do I just take the wire off the dummy light wire and put the new gauge wire on them.

Usually a new wire is run and attached to the new sensor. The old dummy light is left connected.

[frez]

Depends on many factors, such as the gas you put it, how the timing is set up, the state of tune of the rest of the engine, what temperature it is outside, and how you drive it.

For what it's worth, the stock head temp gauge on Corsas so equipped is not an accurate device by any means. It's there so you can track trends, so if the needle does something it normally wouldn't then it's a clue to a possible problem. My 180 would run 350~425, depending on what outside temps were and how hard I was driving it. I always use pump premium fuel, and when it's above 70* outside the lower shrouds come off. 140's are probably a little more forgiving than a turbo engine, but I like to see it at 400 or below. When it's cold outside you kind of get what you get, I went one winter in Chicago where the head temp gauge never moved above 200 it was so cold.

This is great feedback. Thanks. My gauge I am assuming and hoping is broken as it will be around 400 and then after 10 mins of driving will bury over 600. And stay there until I turn off the car and it stays there until I start it again the next time

[66vairguy]

Freez - The problem you describe is either a failed thermistor or a short to ground in the wiring between the gauge and sender. Heat can get to the sender wire that requires a high temperature insulation. Clark's sells the wire from the sender.

Water cooled engine block gauges just check the coolant temperature (typically around 200F). Traditionally air cooled engines, that use air for coolant, monitor the head temperature that is usually the hottest area of an engine 350-400F for a non-turbo. While the Corvair Corsa (and Spyder) temperature gauges are considered inaccurate the main problem is with the sender, and usually NOT the gauge (which was well built). The Corvair, like a lot of pre computer cars, had a temperature gauge that used a "thermistor" sender because it's simple and inexpensive. The Corvair "thermistor" operates over a much wider range than the ones used in older water cooled engines - and that's the problem. I spent months investigating a replacement and found the same issue Clark's found. NONE of the sender companies could get a thermal resistance slug in the range needed for the Corvair. In fact back in the 60's Delco sold the Corvair thermistor to small aircraft companies since Delco was the only company to make a wide range thermistor sender (at least an economically priced thermistor).

Now everyone has gone to thermocouple driven gauges due to inexpensive electronics. A thermocouple WILL NOT WORK with the Corvair gauge. What most of us do is find an old thermistors (they are still out there) to use in the Corvair. The used ones may be off, but once you determine were the needle is during "normal" operation you keep an eye on it and if it starts moving to a higher temperature range you know you've got a problem. DO NOT toss the old Corvair gauge a new sender is in the works.

BTW - Don't confuse the gauge and warning lamp wiring. Even cars with the temperature gauge had an overtemp snap switch on one head to illuminate the dash warning lamp if the engine overheated. Clark's sells the switch and it's a different size for the 140/turbo head vs. the other engines.

[frez]

Thanks 66 I will check the ground and the sender wire. Tomorrow i am putting the temp gun to the engine just so I know what it is running when it pins. The overheat lamp had not gone on other then when I turn the key to start the engine like it should.

[miniman82]

FWIW I have some data loggers here that can read a thermocouple and output a signal that would drive the stock temp gauge with a fair degree of accuracy, but I'm not sure it's something the average owner could accomplish. I have 2 good stock senders right now, so I suppose I'll wait till they die to mess with it. You can also replace the stock gauge with a similar size modern gauge that takes thermocouple input, but none that I have seen are very cheap.

[66vairguy]

Yes the inexpensive thermocouple gauges are not very accurate. A lot of complaints on the car forums.

A good thermocouple gauge will be more expensive if it incorporates cold junction compensation circuitry to deal with the large variations of temperatures cars operate in vs. lab instrumentation that is in a temperature stable room. This type of circuitry has dropped in cost and some of the newer gauges are now incorporating it.

[cnicol]

FWIW, the original post stated GM's topside "ambient" temperature goal was 200 degrees. I don't think that's true for Corvairs and I don't know where you saw that.

Topside on Corvairs runs very close to outside ambient temperature due to the cooling fan airflow drawing in outside air. Turbos are higher due to the presence of the very hot turbo on top of the engine.

Bottom side is regulated to an approximate minimum of 220F. As others have stated "normal" operating temperature depends on a combination of equipment (110/140/180 all would be different), ambient temperature, and load. In my experience 140s run 325-350 going down the road while turbos run 375-425 going down the road, as indicated by the not-so-reliable cylinder head temp gauge.

[jmikulec]

$_1.JPG (18.55 KiB) Viewed 2097 times

Would this be able to work using the water temp as a engine temp gauge.

[jmikulec]

I also found this gauge that actually resembles my gauges. Would this work?

[miniman82]

If you don't have the sender that matches it, no. You could do some testing and see what ranges of resistance cause it to read correctly at certain temps, but people haven't had much luck locating a sensor that will work with these old gauges.

[cnicol]

Check this thread for info on your SW head temp gauge, especially the last post: http://corvaircenter.com/phorum/read.ph ... 084,435846

[Jake]

I just took my 65 Corsa convertible out of storage here in Boston. It’s originally a 180 turbo car but now has the 110

The normal Cyl head gauge reading is around 300 but it’s still in the 30s/40’s here. So it’s the coldest weather I’ve ever run it in
The gauge has budged, almost imperceptibly, I was hoping the sensors fine just the cold weather affecting the sensor temp.

[66vairguy]

I just took my 65 Corsa convertible out of storage here in Boston. It’s originally a 180 turbo car but now has the 110

The normal Cyl head gauge reading is around 300 but it’s still in the 30s/40’s here. So it’s the coldest weather I’ve ever run it in
The gauge has budged, almost imperceptibly, I was hoping the sensors fine just the cold weather affecting the sensor temp.

WOW - this is an old topic revived. Over all these years I finally built a thermal couple box that drives the stock gauges and learned a lot. NO I will not make these up for sale as it was just something to keep me busy so they are hand assembled, no manufacturing cost reductions you get when you make a design to produce hundreds of items.

First - Jake are you saying your gauge is ALWAYS at 300F, if so something is not correct. The temperature gauge needle is "damped" so it tends to stay were it is when the ignition key is turned off. When you start the car with a cold engine, the needle should swing to the coldest indication. If not then it is probably NOT getting a signal from the sender. Keep in mind the temperature sender for the 140HP/Turbo heads WILL NOT FIT the 110HP head hole. Clark's sold an adapter at one time. So if you have a 110HP engine in the car it MIGHT not have a temperature sensor installed.

On the 110HP (and 95HP engines) there was a thermal snap switch to illuminate the over temperature dashboard warning light, it was on the passenger side head. On 140HP/Turbo heads the hole had different threads. A thermal snap switch was on the passenger side head, and a thermistor sender was on the drivers side head to run the gauge.

I don't want to get into paragraphs of things I learned, but on my cars I put thermocouple rings under the thermal snap switch ON EACH HEAD. Now either head will turn on the warning lamp. I use two "boxes" I built with digital readouts of the head temperature. The micro processor board handles the information from a thermocouple receiver board with "cold junction compensation" so changes in engine compartment temperature don't cause an error. The micro proc. runs a driver to control the stock temperature gauges (I replaced the clock with a second temperature gauge). I can verify the gauges using the digital readout at the box and "adjust" the software to optimize gauge accuracy. Yeah a lot of work, but I'm retired - LOL.

Anyway ----- GM did take measurements of how hot DIFFERENT areas of the head get. Obviously the area near the exhaust valve gets the hottest. So the location of the sender or snap switch was a decision the engineers made. It ONLY measures the temperature at THAT area! The temperatures throughout the entire head vary from one area to the next.

As many say --- find what temperature the gauge reads during NORMAL driving and if the needle heads up more than 50F from that, then you should start to be concerned!! BTW just as someone posted here, my thermostat doors start to open around 210F (gauge indication). Idling or slow driving on a 72F day and the gauges sit at about 285F. On a warm day climbing a hill I see 350F. I haven't hit 400F yet, but this summer when there is a HOT day I'll turn on the A/C and find a long grade to climb and see what happens. Just my experience for what it's worth.