Trying to troubleshoot a cooling problem . . .

[av8]

. . . before I unbutton anything.

My normally cool-running '48 F-1 V8 was running on the hot side this morning. I didn't see the gage when it came up, so don't know of it was sudden or gradual. I pulled over, expecting to see a leaking or blown lowere hose (the uppers are new), but the engine compartement was nice and dry. I waited awhile before loosening and removing the radiator cap and discovered that the coolant level was about 1-1/2 inch down from the top of the tank, where it normally is. So far so good, and now I'm beginning to suspect a stuck thermostat might be the culprit.

I felt the upper radiator hoses and tubes (they're new OEM style) to see if one might be cooler than the other, indicating no flow, but both are uniformly warm/hot, as they are normally after the engine is up to normal operating temperature and the thermostats are open.

It seems the next step is to isolate the over-temp condition between banks to check the banks individually, but that won't necessarily tell me if it's a thermostate; it could be a bad sender.

Of course, it could be the gauge acting up but I'm skeptical about that. It's electric and it either works or it doesn't.

Later . . .

After sitting for 2-1/2 hours the engine has cooled down to about human body temperature. The hoses and tubes are cool, and the heads feel the same side for side.

I isolated the senders and the one in the right head drops the gauge all the way to the bottom (cold) peg. The sender in the left head puts the needle just above the the center of the gauge, which is higher than it indicates even on hot days. The ambient temperature during the "overheating" episode was about 70 F. (This eliminates the gauge from the puzzle.)

Any ideas, suggestions, or sure-fire fixes will be greatly appreciated.

[enjenjo]

I think the first step would be to get hold of a hand held digital remote reading guage, and compare that to the dash guage reading. Have the senders been disturbed? I find that very often Ford senders read differently if removed and reinstalled.

[Crosley.In.AZ]

I have no help to add,

I do remember an old saying :" if your flat head is not running hot, you need a new gauge"

[av8]

I think the first step would be to get hold of a hand held digital remote reading guage, and compare that to the dash guage reading. Have the senders been disturbed? I find that very often Ford senders read differently if removed and reinstalled.

The only change that could possily affect the senders is the switchover from 6v to 12v, but I assume that they are filtered through the same voltage drop that my pal Terry used for the instruments. (It wouldn't have occurred to me that the senders were voltage sensative, but I guess they'd have to be , what with Ohm's law and all . . . You can plainly see that I know zilch about electrical devices. Carps' smoke theory makes perfect sense to me!)

I wonder if it might help to loosen and then retighten the left sender . . . :?

[av8]

I have no help to add,

I do remember an old saying :" if your flat head is not running hot, you need a new gauge"

Owning flatheads builds character; one learns to endure abuse and ridicule.

[enjenjo]

Well mike, it has been my experience that Temp gauges are the hardest thing to make work correctly when fooling with old cars.

You can disconnect the left sender, and see what you get with just the right one, as I recall the left sender will work independently too. Then check to see if one bank is really running hot.

You just had it rewired, so the problem shouldn't lie there.

More ofen than not, I find"overheating" problems are the gauge/sender rather than actual overheating.

[av8]

Well mike, it has been my experience that Temp gauges are the hardest thing to make work correctly when fooling with old cars.

You can disconnect the left sender, and see what you get with just the right one, as I recall the left sender will work independently too. Then check to see if one bank is really running hot.

You just had it rewired, so the problem shouldn't lie there.

More ofen than not, I find"overheating" problems are the gauge/sender rather than actual overheating.

I appreciate your experienced assessment, Frank. I'm going to run the truck down to by B-in-L's shop tomorrow and borrow his temp gun to "map" the heat  on the motor and the radiator. At this point I'm betting on a bad left-bank sender; I just turned on the ignition, after the truck sat overnight, and the gauge registers the normal position with the motor at operating temp -- about 1/3 way up. :?

[av8]

Just got a message to my thread I posted on fordbarn from one of the hardcore flatheaders there. It seems the two-pole sender is actually a NC switch (when power is provided) that opens at 206 F to break the circuit and send the gauge all the way to the top, like it reads when the ignition is off -- sort of Henry's idiot light.

The single-pole sender is variable and will indicate differing levels of engine temperature, as long as it has a path through the NC two-pole switch.  Isn't that clever?

My first thought upon learning this was that the one bank could be running too cool or maybe at normal operating temp and the other could be cooking along at 200 F and you'd never know it until it hit the 206 F threshold. Then I thought about it a bit longer and realized that while the coolant flow in each of the cylinder banks is discrete, it's not once it enters the radiator where there is certain to be some tempering from one side to the other and bring the temps of the banks closer to one another.

Flatheads are fun and interesting!

[enjenjo]

So it sounds like you may have had a sender go south.

[C9]

I'm sure it's crossed your mind, but if it were mine I'd stick a pair of SW mechanical full sweep gauges in it.

Or perhaps a pair of SW senders and elec gauges.

I'm guessing you want to retain the factory look on the instrument panel, but you could set the pair of temp gauges below the dash and toward the firewall 2-4" on the left side of the steering column.
Paint the panel black (gloss or flat) and the gauges are pretty much out of sight of everyone cept the driver.

One thing I really like about the full sweep SW mechanical temp gauges is that they are so sensitive.
Mine register 1 degree changes and it's interesting to watch the thermostat open and close - as indicated on the gauge - until the engine stabilizes thermally.

[paul2748]

I installed a single reading sending unit in each head and ran a wire from each sender to a toggle switch and then to the electric guage.  This allows you to see each bank independentally when you flip the switch.

[av8]

I installed a single reading sending unit in each head and ran a wire from each sender to a toggle switch and then to the electric guage.  This allows you to see each bank independentally when you flip the switch.

I like that idea! I wonder if there is a three-position switch that would read either one or the other, or both together . . .  Or, I could get used to the idea of flipping a two-position switch each time I check my gauges, which is often.

[av8]

I'm sure it's crossed your mind, but if it were mine I'd stick a pair of SW mechanical full sweep gauges in it.

Or perhaps a pair of SW senders and elec gauges.

I'm guessing you want to retain the factory look on the instrument panel, but you could set the pair of temp gauges below the dash and toward the firewall 2-4" on the left side of the steering column.
Paint the panel black (gloss or flat) and the gauges are pretty much out of sight of everyone cept the driver.

One thing I really like about the full sweep SW mechanical temp gauges is that they are so sensitive.
Mine register 1 degree changes and it's interesting to watch the thermostat open and close - as indicated on the gauge - until the engine stabilizes thermally.

Jay -- I don't know if I could process all that real-time information without worrying about each small change.

Seriously, I like the idea and considered it for my roadster but never got around to doing it. I might consider doing it when I finish the new motor for the truck, although as well as the original is running, it will probably be next year before it gets replaced.  The T-5 should stretch the usefulness of the old fellow for many additional thousands of miles.

[av8]

It's solved! I drove the F-1 to B-in-L's shop this AM where he "mapped" the cooling system with his high-zoot laser temp gun, and the system is working perfectly, within a degree or two for each point and for each bank, and within a few degrees of the thermostats' set point (160 F).

Jim Leis, who hangs out on fordbarn, e-mailed the appropriate pages from the 1949 Lincoln/Mercury shop manual (along with his own procedure for calibrating the gauge!) this morning, so I was able to determine that the culprit was the single-terminal sender, the one with the variable internals. The first step in the manual procedure answered the question.

Thanks to everyone for the help.  

Mike

[Leon]

I saw a gauge made by one of the major gauge manufacturers that aws a water temp with two needles, kindof like the hour and minute hands on a clock.  Ideal for monitoring both heads.  
I bought one of those hand held digital temp gauges and now wonder how I ever worked without it.  I have been able to locate plugged areas in a radiator, determine which is the feed and return lines on a tranny, check wheel bearings, and even play with tire inflation to get proper wear across the tire.  Well worth the money.