57 F100 gauges trouble

[whalepirot]

New here, not to vehicle forums. I am doing a 'driver' restoration of a nice I6, 3-spd Cali truck.

Stock instruments, gas reads very low while ECT (temp) just started going nearly full hot right after startup.

That combo has me wondering if it's the voltage stabilizer. The fuel sender checked ok. I kinow some gauges read high with too low resistance, and vice versa.

Will a simple voltage reading validate that stabilizer? Thx.

 

[dmsfrr]

IIRC the gauge voltage regulator cycles on & off to give the gauges an adjusted average voltage.
I don't think measuring it for an actual adjusted voltage output will work.

 

[whalepirot]

IIRC the gauge voltage regulator cycles on & off to give the gauges an adjusted average voltage.I don't think measuring it for an actual adjusted voltage output will work.

Thanks for the quick reply!
It appears to be doing just that. I didn't find it either!

The service manual has much better test procedure than I expected and the temperature gauge issue points to the sending unit.

 

[whalepirot]

Manual procedure result for the temperature points to the sending unit.

The fuel sender was worn and out of stock, so I adopted a phrase learned here: Don't buy it if you can make it!

Opened the 'can' that houses the slider (3 metal tabs) to reveal the interior caked with black crub and rust.Scraped that elan, rinsed with brake cleaner then tested the winding with my DVOM rpobe, slid along that like the pickup does. Those resistance readings were a constant change, not jumpy like from the slider, as I move the float.

The hole that the pickup rotates in was oblong not round, in the removed 'cover' part, whick allowed the slider to move all over the place, giving those crazy ohms.

I chose to take a 1.75" square of 16 gage sheet metal to make a cover (cap) piece with a round hole for the pickup. Two small rivets, flatter side inside so as not to interfere with the silder, inside the housing, holds it together very well. The newly drilles 5/32" hole keepos the slider where it should be, and ohmage smoothes out as it varies with movement.

The gauge seems fixed.

 

[whalepirot]

Fig. 2 on a Fordification page has a pic of the fuel sending unit http://www.fordification.com/tech/fuel-sending-units.htm

It shows the 'can'. I "wrapped' the other side.

Filled 'er up yesterday and drove a while. Yessss, the 60 year old fuel gauge seems accurate!!

 

[whalepirot]

Anyone have the resistance readings for a properly working engine temperature sending unit? This one is 27 ohms at room temp, that value dropping with heat applied from my hot air gun.

 

[dmsfrr]

Anyone have the resistance readings for a properly working engine temperature sending unit? This one is 27 ohms at room temp, that value dropping with heat applied from my hot air gun.

First photo,
No clue if this one is any good or not... it should be the same as '57, from a '58 head.
It measured 220 ohms at 60 degrees and went down to about 50 ohms when I put the business end in some nearly boiling water.
It's the same sender as the bottom one in the 2nd photo.
.

 

[whalepirot]

First photo,
No clue if this one is any good or not... it should be the same as '57, from a '58 head.
It measured 220 ohms at 60 degrees and went down to about 50 ohms when I put the business end in some nearly boiling water.
It's the same sender as the bottom one in the 2nd photo.
.

Looks like it, 1/8" NPT threads. Somewhere I read resistance should have a 50 ohm range, so all three suggest this sender is bad, agreeing with the FSM test.

I flushed the DexCool which is maybe a year old, just in case, then refilled. There was a rusty glob that came out. The outstream tripled after less than a minute.

 

[whalepirot]

So, there is plenty of variance in discussion of these senders. the temp gauge worked okay for some time, then went nearly full hot, even upon cold start.

Other threads speak of: wrong sensor can fry the gauge/ long tailed is correct/ unstamped is a 6volt/cannot measure resistance due to internal points/polarity is/isn't important, etc. In all, not too definitive. Even one "old Ford place said the one I have is wrong for this truck, while old Ford sources show this one being correct.

Such a complicated process for a task that's about as simple as they get, and on a simple vehicle to boot!

 

[willowbilly3]

Since Ford has not been known for blazingly accurate gauges, it does get a little tricky. I was able to clean my fuel sender good and replace the float. A few trips in and out of the tank to tweak the arm got the gauge range as good as can be expected although the second half of tank is bigger than the first. My temp gauge comes up real fast and levels out a bit on the hot side. In the past, I've checked my engines with good manual gauges at the engine, then marked with white-out where that correlated for normal operating on the gauge.
Also worth noting, coolant temp senders need to be immersed in coolant. Some engine designs leave them in a pocket of air (or steam) if you don't burp the cooling system good.

 

[dmsfrr]

Looks like it, 1/8" NPT threads.....

(mistakenly left out of my previous comment)
The '57+ temp sender is 1/4 inch pipe thread, the '56 and earlier is 3/8 inch pipe thread.

 

[whalepirot]

coolant temp senders need to be immersed in coolant.

Thx. I had that issue with another car and this is definitely in the coolant.

The '57+ temp sender is 1/4 inch pipe thread.

The correct sender arrived from LMC today and works great. I think I misspoke the size... old brain!! I've had poor luck with their lousy shipment packing, but it and new tinted glass came okay.

The gauge rests low-side when the cool engine is started and a short trip on a cool day only had it reach low normal, which I believe is correct. Nice to have the gauges okay again, especially 60 years old, like 95% of the rest of this truck.