overheating 1954 Manhattan

[oldpm]

Good Morning all.
My 54 Manhattan's temp gauge has been pegging on hot for several months.  The car is not driven much but it always shows hot.  No other signs of over heating; loss of performance, funny noises, smells, just normal excellent running.  Yesterday I used the kitchen thermometer trick and it read 170 degrees.  What is the operational temperature for this engine?  Could the problem be the sending unit?
Any advice would be great and much appreciated.
Thanks
Barry

[joefrazer]

I would replace the sending unit that's located in the head. They usually fail and read low but I have seen the opposite occur.

Another problem could be the instrument voltage regulator located on the back of the cluster. If they fail you will see high heat gauge readings.

[jmxkf1]

I'm into my second '53 Kaiser and it still has same problem.  I've changed sending unit a few times and changed instrument voltage regulator more than once.   All parts are NOS and purchased either from Walker or from Rudy so I'm sure the parts are as good as it gets.   I have new radiator too.   The first '53 I had I even rebuilt the motor but same issue with temp reading too hot, almost pegged on high.   
I checked wiring and nothing is frayed.  If you figure this one out please let me know.   thanks,  Jim

[boatingbill]

My Dad's '53 did the same thing. We removed the thermostat with a lower temp unit and still no luck. The cure was a back flush of
the motor and scale and rust came out and mostly fixed the problem. After that we replaced the thermostat with the correct one and
it would run high normal.

[MarkH]

Just read an interesting article in the 5-25 issue of Old Cars Weekly about Cadillac & Lasalle flatheads running hot due to rust & sediment collecting in the back of the block. The cure was removing the rear freeze plugs and one rear headbolt that reaches the water jacket & flushing.

[r1lark]

Block flushing - this is a very beneficial thing on old engines. It's amazing what crud builds up in the block's water jackets over the years - not to mention the core sand that may not have gotten removed when the block's were cast.

Think about it this way - what's the first thing done to an engine that's getting rebuilt (after disassembly)? A thorough cleaning of the block. "Yep, got that baby rebuilt and she runs cool as a cucumber now." Wonder if just cleaning the cooling passages and water jackets might have accomplished the same thing?

I know from experience how crudded up water jackets can limit the cooling capability of an engine - in my case on Studebaker V8s. It's a nasty tough wet dirty job to clean the water jackets out properly. Don't shortcut it - pull all the freeze plugs, scrape, flush, repeat, repeat, repeat. 😁  If you have a pressure washer, use that.

Zero cost if you can do it yourself, and it may save you the cost of a unneeded rebuild.

[Corsairdeluxe]

Do it my way, imitating the old DuPont#7 flush that really works on cast iron engines.
Flush with water until it runs clear
Add 8 oz of oxalic acid. Top off ,block radiator if necessary to make engine run hot Run at fast idle 30 min. Drain ,should look like strong coffee.
Flush with water until clear. Add 8 oz of TSP. trisodium phosphate. Block radiator and run for another 30 min.
drain and flush till clear.
No currently sold flush is much good on a our cast iron engines.
The chemicals are dangerous and care should be used. I have done this 30-40 times over 50 years and have had no trouble.

[oldpm]

Many thanks to all of you that answered.  I now have some direction to follow. As I said, I don't think the engine is overheating so I will start with the sending unit.
Thanks again,
Barry