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Temp gauge

smfulle

smfulle

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Ogden, Utah
Ever since I got my truck back together the temp gauge has moved up almost to the peg and mostly stays up there. I have never had a boilover and have 16,000 miles on the new engine.
I have tried several different temp sending units and they don't seem to change anything. I have a 180 thermostat installed, and when I put the infrared thermometer on the temp sender location it reads right around 180 plus or minus a little when the gauge is close to the peg.
The fact that the infrared shows no overheating makes me ok with driving it with this high reading, but what I do worry about is the one time the engine is actually hot and I ignore it because the gauge has always read high, and then I'm rebuilding my engine.
Any ideas on how to get the temp gauge to calm down a little? What are the standard temp readings on these stock gauges at the halfway mark and all the way right mark?
 
if you are using a mechanical type sender, one that has a metal bulb on the end of it, it is a possibility that it may be going bad or that heat coming off of the exhaust manifold is touching the sender cable, if you are using a newer style sender where it just screws into the block and you run an electrical wire to it, then it is possible that you may have a bad ground at the sensor body itself. i had the same problem with a set of aftermarket gauges and when i put the sensor in the water jacket of the block i used teflon tape to seal it up so i had no leaks, sounds simple right? pipe thread usually needs teflon tape to seal, so i went for it and put it in and found after hours of searching that it was a no no.
Didn't wind up finding the solution for quite some time, come to find out the sensor body had a slight taper to it and that's how it wound up sealing in the block.

so if its the mechanical style i would test with a known good sender and gauge, if its the newer style i would take a piece of wire and wrap around the body of it and put the other to a ground and see if that helps.

if anyone believes that i am in the wrong please correct me
all im trying to do is help out the best i can
 
I don't think your wrong! and think your RIGHT, for helping a fellow Truck Owner out!
That's why they call this a Forum.. Ive had this similar problem and was wondering
Myself! brumly07 Thanks for the Tip!:)
Allen
 
I do have the teflon tape on mine. I'll pull it off tonight and see if that changes things. One of those things that is right in front of you that you should think of but don't. One wire to the sensor. Where's the ground? Obvious but not. THanks!!
Stan
 
Well, I pulled the sender out and cleaned out the Teflon tape, then put it back together. Then I went for a little test run. The gauge was a lot steadier and didn't go quite as close to the peg, but it still seems pretty high. I suppose if I took out the 180 thermostat and went to a cooler one the reading would probably be more in my comfort zone as far as the gauge goes, but then the heater doesn't work as well. Anyway, here's a photo of the gauge after my test run and idling. Please ignore the dust. Darn camera flash sure makes it show up.
100_1578_zpsf9841af6.jpg
 
Electronic Gauge Testing

Both the sender , and gauge head must be *perfectly* grounded else it'll never read right .

The previous advice was very good , now it is time to test the gauge head :

Key on , engine off , disconnect the sender wire from the sender and wrap it in a rag , go look at the gauge ~ it *must* be pegged , if not the gauge head isn't properly grounded or it's defective . be aware these old gages almost never fail .

Now , go ground the sender wire to the battery's negative post , using a jumper wire ~ this *must* drive the gauge to the other extreme .

If it passes both tests , the gauge head & dashboard is fine , add a ground strap from the cylinder head (rocker box screw) to the firewall to properly ground the circuit . don't waste time worrying about the current grounds , just do this as the gauge is very sensative and needs a closed loop ground path for accuracy .

The original engine to gauge ground was a woven strap , they're often gone missing and I find them on American cars & trucks in every junkyard I hit , save the correct hex head self tapping screws too .

If the gauge dodesn't pass the grounded / open circuit test , remove the gauge binnacle and wire brush both the screws holding the gauges to the binnacle and the edges of the gauges , then add one ground wire from the binnacle to the dashboard proper , this should also make the fuel gauge more accurate at the same time it fixes your temp. gauge .
 
gauge

Was the gauge working properly before the new engine was installed?
Did you ground the engine to the truck body? A bad ground couild cause this problem.
If you need a different gauge to try, I have the original gauge cluster out of my 58. No idea if they work, I replaced them with VDO gauges before I installed my engine. You may have the gauge or the whole cluster if you want it, just pay the shipping.
Rebuilding engines isn't cheap and not knowing for sure what temp it is running at could be costly.
Good luck
Gerald in Florida
 
Thanks Nate and Gerald. Engine and gauge grounds might be suspect. I'll make some time to get those checked and updated. Starting second job this week so my tinker time is going to go down in a big way, but I really do want to get this sorted.
I suspect that there may have been some gauge issues with this truck when I got it. It was not running and the previous owner had installed one of those cheep gauge clusters under the dash that I hated. I got rid of that and hooked up the originals and was a little surprised that the needles all moved and seem to function.
One other thing that makes me think that you might be right on the gauge cluster not being well grounded is that the fuel gauge has a tendency to jump around from time to time. At first I thought it was due to fuel sloshing around, but it sometimes does it when standing still
 
I also heard there was a difference in OHm's on the senders that go in the block.
If I remember well there was a difference of 30 ohm and 90 ohm.
So the gauge will give a wrong reading, using the wrong sender.
Problem with the fuel gauge is as they told you before about the ground issues.
there is a wire that goes on to the sender on the tank(behind the seat) and to the floor of the cab to make a ground
The screw that holds it to the cabfloor is usually corrosion/dirt affected.
Also the sender in the tank is of a slider type,who are very sensitive when they get a little wornout/corroded
Hope this helps
Tony
 
Another thing to check but I'm sure you have... is the cooling system bled? An air bubble can cause a high reading too.
 
First, how good are ALL the wires in your truck? The 55 had a mechanical gauge and starting in 56 they went to the electrical sending unit but either way a cooking thermometer and a handful of different ohm resistors will get it reading right. FIRST, follow above advice and get head and gauge grounds. I like to run temporary jumpers from the head and gauge housing to the negative battery post to absolutely eliminate the ground issue even though everything else works properly. Remove sender from head and hook a wire to the threads using either a big alligator clamp or a stripped back bare wire and a small hose clamp. Route to battery negative post. Hook up sender wire direct or use a jumper to give more leeway and submerge in a pan of water you've heated to 180 degrees. See where the gauge reads--it should be about mid-range. If not there's a good chance the gauge itself is in error. We have a variable resistor to vary the ohms and then use the correct resistor from Radio Shack to get the gauge reading in range but only as a stop gap procedure till a correct reading gauge is found or an old gauge rebuilt if from a rare vehicle.
 
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