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Temperature sending unit location?

 
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Herr Otto
4 BBL ''Hyper-Pak''


Joined: 29 Sep 2009
Posts: 27
Location: Chicagoland

Post subject: Temperature sending unit location? (Wed Sep 08, 2010 1:47 am) Reply with quote

My 65 Slant six is in a 49 Dodge truck. The 49's temp gauge is mechanical and the sending unit will not reach the front of the head. On the 65's block on the passenger side towards the rear is a brass plug, and when removed ,coolant comes out.
1. Is this a suitable place for a sending unit or does it have to be in the head?
2. In addition I am having my 65 radiator re-cored, would it be a good idea to have a fitting soldered into the top tank to add a sending unit there? That one would have to be an electrical unit as it is too far for any mechanical.
3. Anyone have good luck re-soldering a capillary tube with a new sending unit after freezing the ether in it?

Thank you,
Herr otto


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Joshua Skinner
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Joined: 27 Jan 2005
Posts: 6910
Location: Portland, Oregon

Post subject: (Wed Sep 08, 2010 7:58 am) Reply with quote

The temperature sensor goes in the front of the head because that's where the hot coolant comes out. If you put the sensor anywhere closer to the coolant inlet it will read lower. In case you didn't know the vast majority of the coolant comes into the block from the water pump, goes front to back through the block, up into the head, forward and out. Some coolant comes into the head under the exhaust ports and some always bypasses the radiator if you haven't plugged the bypass at the water pump. If your original gauge works I'd put it wherever it will reach and be aware it's going to read a bit low.

The upper radiator tank is a poor place for a temp sender as it's in cold coolant until the thermostat opens and if the coolant gets even a little bit low it won't read properly. I tried this myself years ago as my '74 Duster had a bung in the top tank for an emissions vacuum switch.



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powerwagonpaul
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Joined: 24 Oct 2009
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Post subject: (Fri Sep 10, 2010 9:20 am) Reply with quote

the temperture in the head is what matters, that is where combustion takes palce, that is where heat is generated. here is what i would do, i wouls hook the 49 sender to the block, then i woukld hook up an idiot light sender to the head port. that way you can monitor the temp with the gauge, but not knowing waht is is really telling you (degrees), the light will tell you if it overheats. Wink



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Wesola78
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Joined: 04 Nov 2002
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Location: Cypress, Texas, Northwest Houston. The Lone Star State

Post subject: (Fri Sep 10, 2010 4:40 pm) Reply with quote

I don't have anything to add, the other guys nailed it.
However, I would like to see pics of your '49!



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Sam Powell
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Post subject: (Fri Sep 10, 2010 5:06 pm) Reply with quote

I have temp sensors in both places, and after the engine warms up, they read the same. The block warms up more slowly by about 20 degrees until the engine gets fully warm, which takes about 10 minutes in moderate weather. It would take longer in cold weather. After five minutes the head gauge (via the lap top through the ECU) will say 195 and the block gauge will say 175. After 10 minutes, they both read 200.

Is this a carb, or EFI induction? If it is carb, you are not controlling warm up enrichment of fueling with your temp sensor, and it does not matter to the engine if you're seeing combustion chamber temps or not. Once you learn the normal patterns on the gauge with a healthy cooling system, you will be able to use the gauge to tell you when things are not right, just as if the sensor were in the head.

I think you can put the sensor in the block and use it with no real concerns other than to learn your own car's normal behavior. The original electric gauges in the stock A bodies were notoriously unreliable anyway. They did not have degree markings, just vague generic terms, like cold, and hot. A real gauge in the block will give you more information.

Sam



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Herr Otto
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Joined: 29 Sep 2009
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Location: Chicagoland

Post subject: (Fri Sep 10, 2010 6:26 pm) Reply with quote

What is a normal temperature I should consider safe once warmed up? I beleive my thermostat is 190 or 195 degrees.
Wesola78, if I knew how to post a picture of my truck I would.
Herr Otto[/img]


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Sam Powell
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Post subject: (Fri Sep 10, 2010 7:35 pm) Reply with quote

It will not hurt your engine to run in the 210 range. My 95 Corvette was designed so the first electric fan did not come on until 220, and then the second one at 225. But, this requires good hoses, heater core, and radiator. My engine runs at 210 on a hot day, and it is fine. If there are leaks in the system, and will not hold pressure it is likely to boil over at this temperature. However, all these components in my cooling system are nearly new. The bottom line is, if it is not boiling over, you are not in trouble. However, if it never gets up to full temp, which is around 200 degrees your engine might be wearing out faster than it needs to.

Ironically enough, the hotter your engine can be made to run without boiling over, up to a point, the more efficiently it will run, and the better wear you will encounter between moving parts. Engines with 160 degree thermostats have been proven to wear out much faster.

With a 190 thermostat it will likely run 200-205. If the sender is in the block, assume the head is 20 degrees hotter than the block until it has run at it's max temp for 5 minutes or so. Then it all evens out.

When I first installed the EFI on my engine, I had the ECU sender in the block, and it ran in enrichment mode too long that way. So, I switched the sending units and put the gauge in the block and the ECU sending unit in the head, so the ECU knew what temp the combustion chamber was. It has been this way for years now, and I know what normal readings are for my car.

Sam



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Last edited by Sam Powell on Sat Sep 18, 2010 6:10 am; edited 1 time in total
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olafla
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Joined: 17 Jan 2006
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Location: Oslo, Norway

Post subject: (Fri Sep 10, 2010 7:44 pm) Reply with quote

Hi Herr Otto, you can click on this link and read about how to insert a picture (and other useful things!)

Olaf



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itlldo1
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Joined: 15 Jan 2007
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Post subject: (Fri Sep 17, 2010 8:36 am) Reply with quote

I've got a 49 1 ton Dodge, and a 36 Plymouth. The probe for the temperature guage is factory mounted near the rear of the driver's side of the head. Perhaps the guage is designed to indicate the temp at the location of the probe. Those flathead engines used water distribution tubes to funnel water to the rear valves on the opposite side of the engine. I'm assuming that the probe mounting was important to show that the rear of the engine was getting sufficient coolant flow. Mike



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