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Old 11-26-2012, 03:40 PM   #16
KacyC3
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yes the ecm in my car will reads the temp of the heads for controlling a/f ration and fan while my gauge is next to t stat. My ecm will read up to 230 if there is an air pocket in the cooling system while the gauge reads much less. But when full it reads about the same, are you sure you don't have air in the system? I bough http://www.dormanproducts.com/p-20810-902-112.aspx from my local Oreilly's and an adapter to use them to burp my system .
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Old 11-26-2012, 04:50 PM   #17
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Interesting that the temp could vary that much between the head and the thermostat. Thinking........regular flow would have cooled water being pumped into the engine from the bottom of the radiator.

Water then passes up through the block, heads and out the front of the heads into the intake and is then returned through the thermostat to the radiator for cooling.

The thermostat will generally restrict water flow until the operating threshold temperature of the thermostat is reached. Once it reaches that threshold it would be wide open until the engine cools below that threshold.

I know that aluminum heads dissipate heat much quicker than their cast iron counterparts so that could play a part; however, 30 degrees seems like allot to loose in that short distance between the head and the intake.

I assume you're not running a reverse flow setup. Actually what your seeing would make more sense as a reverse flow. I believe some of the C4 cars had reverse flow systems, not sure what years.
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Old 11-26-2012, 06:04 PM   #18
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Hi Sly,

You probably don't want to do this, but I'll toss it out anyway just because it might be neat to do. Go someplace that has an IR camera and see if they can take a picture of the engine. You could see all the temp deltas across the entire engine, if the camera can read that range. An insulation company would be a good place to try. Not that it would tell you what you need to know, but might be interesting. You could see all the hot spots, difference between inner and outer cyclinders, water pump, etc. You could probably talk them into taking a couple of shots for $10 or free if you give them a ride.

We use IR cameras at work every once in awhile to double check our designs...just in case we missed something. I've seen some that are pretty darn expensive, around $300K. The sensor was even cooled w/nitrogen (I think) and was used to look at 2 mil bond wires in a transistor.

Good luck!
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Old 11-26-2012, 07:43 PM   #19
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This car and engine,though not stock,is all pretty much old school. No aluminum heads standard cooling system except for electric fans.
A air pocket at the t-stat housing may be the problem... I think a bit of burping is in order. There is a small hole in the stat that I drilled prior to installation and when the temp hits 180 at the stat coolant flows freely.
I have never had a problem with air pockets before that I know of. Prior to the first Autometer sender going bad I could run all day at 180 degrees regardless of the ambient temps. and this reading of 210 now is confusing. Perhaps the first Autometer sender was reading too low?
I don't really think I have a serious problem now and would still be blissfully unaware of the temperature variant now if it weren't for the recent acquisition of this fancy new IR gun. Has anybody that has an IR gun ever checked their engines to see how much of a temp change there is from say head to intake? I'm thinking that perhaps the area around the temp sender is hotter due to the fact that it is near an exhaust port or something to that effect. Just guessing at this point.
I do have access to a Thermal Imaging camera. I'm a retired firefighter and we used one to search for different temp. signatures all the time. Next time I'm near the city I used to work in I will stop in and see what things look like under the hood...Good Idea!
Thanks for your time,guys....
Sly
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Old 12-16-2012, 09:01 PM   #20
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Update...

I had the opportunity to look at my eng with a thermal imaging camera a week or so ago at the firehouse I retired from and the picture it gave was interesting.
The engine for the most part runs at a temp of about 190 with a ribbon of heat circling the eng. at the level of the heads of about 210 degrees. The intake( mine is aluminum)is one of the cooler parts of the eng at about 180 degrees. So if the sender is mounted in the head as mine is I am reeding the right temp for that location. If I want to get a lower reading I guess I could move the sender to the t-stat housing. I doubt I would do that though. Knowing that the eng. is not overheating is all I'm looking for and as long as it stays at a constant 210...I can live with that.
It was interesting to see the variance in temps from one place on the eng. to another.
I would like to do another eng that is similar to mine as a comparison so if anybody with a 350 with headers and a aluminum intake is ever in the Detroit area...Give me a shout.
After I get my car back from paint in April that is!!!
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Old 12-16-2012, 09:35 PM   #21
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Got any pics of the IR image?
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Old 12-17-2012, 12:31 AM   #22
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Quote:
Originally Posted by mbwalker View Post
Got any pics of the IR image?
Nope... Took a few but it didn't come out well with the protective cover that is on the screen of the camera.
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Old 12-21-2012, 10:50 AM   #23
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Adjusting the guage

I have never posted before but I see this question come up a lot and I have personally suffered through this problem. The gauge has a fixed amount of resistance and the sending unit has a variable amount. The gauge acts as a comparator to its resistance and that of the varying sending unit. If a fixed resistor is added to the sending unit a non-linearity is introduced and the circuit will not report the temperature accurately over the full range. However if the gauges resistance is changed all works well. On my 68 I added resistors across the back to adjust the gauge. This works great (given that the gauge is reading high). Adding resistance in parallel reduces the gauge's resistance and has the same effect as scaling the sending unit to a higher range. I don't recall the exact resistance I added. I did a little math to get it right but that only got me close so I did a bit of trial and error to tweak on it. Hope this helps.
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Old 12-21-2012, 12:56 PM   #24
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I am not sure because I don't have your model or engine, but you wil usually find different temps in different areas along your engine block in slight small amounts. The intake will be cooler because of the air flow. Normally manufacturers place the engine coolant sensor in the place where the engine will run the hottest. Normally in the head where the water exits to return to the radiator I would guess. Thats where you want to measure the temps to insure its not over heating the fastest.

Also, you can get a cyclinder that over heats while others do not, thats why a laser temp gauge is good. To measure individual cylinders. Helps determin a fuel flow issue on injected engines great. Less fuel means hotter cylinder and possible injector problem.

But back on topic, if your gauge reads 210 and the laser temp gauge reads 210 at the point where the sender is mounted and thats the hottest spot on the engine, I would think you are working perfectly.

On the aftermarket gauges and sending units, you will sometimes find the actual gauges have a small screw that allows you to adjust them for accuracy.

Good luck and I hope the best for you.
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Old 12-21-2012, 04:21 PM   #25
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Thanks for your comments,guys.
All seems well. The car is running great and is now in the shop for new paint.
I will be changing the clutch in the Spring after approx 30,000 miles of use and I did find a small amount of play in the right side trailing arm bushing. Other than that all is right with the world!
Thanks again and MERRY CHRISTMAS!!!
Mark
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