66 289 temperature question please

[shelbyhertz66]

Hello,
I am trying figure if my temp gage is reading correctly?  It is reading much farther to the hot
than any of the several mustangs and shelbys  I have had have read.  It could be sending unit or thermostat
but what i am wondering is I purchased a laser temperature gun when the engine is fully warmed up
where should I really point it to get an accurate measurement? .
thanks much!

[shelbyhertz66]

  When I really think more about this It seems to me that the top tank of the
  radiator would be the spot since thats where the hottest coolant is returning?
am I wrong? 

[FL SAAC]

Measure coolant temperatures at the close end of the return line just before it enters the radiator. Remember that surface temperature will vary slightly from internal temperatures – some 10 to 15 degrees. Pick a spot with small thermal mass, like the top radiator hose connection.

[FL SAAC]

FYI

Water Temp Gauge Reads High - Autometer

https://www.autometer.com/blog/faq-post/water-temp-gauge-reads-high/

[pbf777]

It could be sending unit or thermostat, but what i am wondering is I purchased a laser temperature gun when the engine is fully warmed up
where should I really point it to get an accurate measurement? .

     Establish the relativity of the gauge reading by pulling the sending unit out of where it is installed (intake, behind the thermostat?  ) and drop it in a pot of boiling water; the gauge will provide the observation of what 212° +/- will look like.   

     As far a the infrared temp-guns, these are not terribly accurate, particularly as their implied values are sensitive to the reflective nature of the surface being targeted.   

     Scott.

[shelbyhertz66]

thanks everyone so far for the ideas much appreciated!
I did try the laser measurement at the top metal connection point
of the rad hose 204 degrees, don't know if thats really indicating a too hot engine cond.
I will have to try checking the sending unit. If anyone just happens to have their 66
running at full temp and could shoot that same spot for comparison that would be great
but that's asking a lot.
anyway thanks again always great help here.

[greekz]

My 66 runs about 170 depending on the weather.  What degree thermostat are you running?  Also, when is the last time your radiator was serviced and/or the coolant changed?  These might be factors.

[shelbyhertz66]

so I pulled the thermostat today and it is a 195 so I installed a 180 and will see tomorrow
if it made any difference. I did see some corrosion in the radiator not a ton but some ,I may try
getting a new 3 row radiator, it looks to me that the original has 3 rows but possibly a new one period
will improve. also checked the head gasket to see if they are on correctly and if what i understand is correct
the (tabs) or corner of the gasket is showing bottom front corner of each head. With summer driving ahead
I really want to find the cause, its just not an issue I have ever had.

[sg66]

It could be sending unit or thermostat, but what i am wondering is I purchased a laser temperature gun when the engine is fully warmed up
where should I really point it to get an accurate measurement? .

     Establish the relativity of the gauge reading by pulling the sending unit out of where it is installed (intake, behind the thermostat?  ) and drop it in a pot of boiling water; the gauge will provide the observation of what 212° +/- will look like.   

     As far a the infrared temp-guns, these are not terribly accurate, particularly as their implied values are sensitive to the reflective nature of the surface being targeted.   

     Scott.

Adding to this, you want to check the resistance as the temperature increases. I had a bad sender that read 11 ohms at 172 degrees in a pot of water on the stove. (reading high temp on gauge), The new one I bought showed 18.5 at the same temp and was right on the money on the gauge and went to around 35 ohms at 180 degrees. Reading through an old email discussion I had with Jim Cowles about this, I bought a Duralast version of the smaller 65 sender - TU22 part number that was manufactured by Wells Vehicle Electronics. At the time, they also had the engineering specs online showing the expected resistance at temp. The engineering drawing is no longer online that I can see but this is their sender and I would buy it again if needed https://wellsve.com/parts-search/?partNumber=TU22 Autozone website shows their TU22 is now made by Rostra Powertrain Controls and I have no idea if it's accurate or not.

As far as the accuracy of your IR thermometer, boil some water, it will be 212 degrees. Your IR  may be a few degrees high or low but shouldn't be off much. The best place to measure the coolant temp is with the cap off the radiator but only do this after letting the car warm up WITHOUT the radiator cap on. Once you know the actual coolant temp coming into the radiator, you can get the temp of the upper and lower hoses to get an idea of the temp drop after going through the radiator and factor in any difference for the rubber insulating the actual temp. I recall around a 20 degree drop after going through the radiator.

According to Jim, even the NOS sending units were not accurate so the best bet is checking the resistance of whatever you use to know what you're working with.

Steve -

[NGT350]

I confirmed my temperature with two different IR guns, and measured the resistance on multiple senders. The senders varied widely. I picked the closest to stock (motorcraft branded)and installed a resistor in line that brought the resistance in spec. Now reads just under middle on the gauge at operating temp.

[shelbydoug]

It appears that you have confirmed the actual operating temp as normal but the gauge reading insn't?


You didn't ask the question and no one else mentioned this but there are only two temperature senders that is accurate. That is the original Autolite and replacement Motorcraft. Both will be stamped with ID into the unit itself.

NONE of the aftermarket senders are accurate. They will ALL read too high on the original gauge. 2/3 up on the gauge where as it should read1/3 to 1/2.

I'm not going to get into all the idle speculation as to why others are wrong but other  then some junior tech engineer made a mistake in spec'ing the resistance, no one was there to check the accuracy of the revised listing and it was picked up across the replacement industry and "standardized" by just more of the same incompetence of operation.

There are other examples of this procedure happening across the industry such as the current listing of spark plugs, BF32's being the same as BF42's. Obviously they are not but that is what the current listings indicate incorrectly.



The main issue here with this temp sender is that the Ford Autolite/Motorcraft has been out of production for more then a few years and the only place you can find one is somewhere like Ebay and expect to pay $100 or more for one IF you can find one.

[shelbyhertz66]

Hi All,
My thanks to all who have helped ,it is much appreciated that you took the time.
Partial update .
the thermostat change did drop the gage to within an acceptable range based on what the readings
have been, also I found that the short bypass hose from the water pump to the thermostat housing was
cut too long by someone and was kinked so the flow was restricted by at least 50% I am checking a source for
an original sender . Also replaced coolant with new proper mixture. Might replace the rad but want to get some
test miles before doing so as its original.
Best