temp gauge troubleshooting

[dmac0923 10]

ive been trying to troubleshoot my temp gauge on my 69 mach non tach dash.

 

the needle is constantly reading at the first hash mark after the C regardless of the engine temp.

 

I have replaced the sending unit twice , making sure both times it was one for the gauge and not the idiot light. still nothing from the gauge.

 

If i take the wiring harness connection off the sending unit and ground it to the block the temp gauge needle swings to the H mark and returns when the wire is removed from the block.

 

the oil and fuel gauges work fine so i dont think its the instrument voltage regulator.

 

i have installed a new printed circuit board.

[jmlay 80]

Did you put sealer on the threads? If so it is likely not grounding to the intake. Take a jumper wire & connect ground to the body of the sensor NOT the wire connection. IF the temp reads "normally" then take the sensor out & remove the thread sealer.

[LoneWolf2U 136]

First verify the guage is working in full range.

Remove sending unit wire and gorund it to the block.

Turn key to ON and the temp guage should go to full hot.

If it does, you may have a ground issue, IE no ground from block to frame.

[dmac0923 10]

I took the sending unit out and tried to scrape off as much thread sealer as possible. When I was inspecting it, the threads cut through the seler so it should have made good contact.

 

 

Yea with the key ON the gauge does go full range when I ground it to the block.

The battery to block ground is clean and tight

[LoneWolf2U 136]

Threads cutting the sealer doesn't mean the connection was good.

It takes more than just the edge of the threads to make a soild ground.

Remove the sealer, its a pipe thread that should not leak if tightened.

 

The batt to block ground is only half the ground requirements, There was block to firewall and block to frame straps from the factory to insure proper funtion of lights and guages,acc.

[dmac0923 10]

Really? Do you have any pics of the grounds?

[smh00n 87]

So this is an old post, but it (and others on temp gauge issues) has saved me today.

My brand new motor build resulted in no temperature gauge working. After chasing it all down, verifying both senders I had actually did work and had the required Ohms cold, I found out that the alloy adaptor I used to put the gauge sender into the manifold wasn't grounding properly. A wire from the body to the frame confirmed this.

So, now I need to get a steel adaptor for it. But, will the alloy inlet manifold also not allow it to ground? I have used thread sealant on both the adaptor and sender (and also the Sniper temp sender) so maybe this is not the issue?

FWIW, I have 0 gauge earth wires to both block and frame direct to the battery, and the Sniper temperature gauge works as it should, as does the oil pressure gauge and light, so I have good grounds from the lump.

[Midlife 814]

Thread sealant acts as an insulator.

[RPM 1,190]

On soft metals like aluminium and brass I don't use sealant. 

[smh00n 87]

Noted.

I will remove the offending product and see what does.

[smh00n 87]

To further hijack this thread I have a question on voltage.

My gauge now works after removing the sealant. However it reads a bit high - the needle sits on the first leg of the 'M' in TEMP at around 185° which seems to be its' happy temperature.

I have an adjustable voltage regulator and have 4.97 volts going to the gauges. Does this voltage affect the reading scale or is that scale mechanically adjusted in the gauge? I saw another post about how to adjust gauges with the ratchet wheels.

I can change the sender back to the original one, as I only replaced it as everything else on the donk was new and I didn't want it to miss out.

[jmlay 80]

Some good reading in this post. Unfortunately it is a quite a bit of reading:

https://www.vintage-mustang.com/threads/still-running-hot-will-bb-fan-fix.1212401/page-5#post-10809926

[Midlife 814]

The constant voltage regulator can be adjusted but it affects the fuel, oil, and temperature gauges.  On the back of the CVR is either a small post or screw, often potted in epoxy.  Turning it one way or another changes all 3 gauges at the same time.  My preference is to ensure I have a 1/4 tank of gas, and set the CVR so that the fuel gauge reads 1/4 tank exactly.  Both the oil and water gauges are "indicator gauges", in that once you determine where normal is, once they deviate from that position, then something is amiss.  They are not precision instruments.

[smh00n 87]

8 minutes ago, Midlife said:

The constant voltage regulator can be adjusted but it affects the fuel, oil, and temperature gauges.  On the back of the CVR is either a small post or screw, often potted in epoxy.  Turning it one way or another changes all 3 gauges at the same time.  My preference is to ensure I have a 1/4 tank of gas, and set the CVR so that the fuel gauge reads 1/4 tank exactly.  Both the oil and water gauges are "indicator gauges", in that once you determine where normal is, once they deviate from that position, then something is amiss.  They are not precision instruments.

Thanks. I have an aftermarket one, but it has the potentiometer on it. Like I said, I dialled it up to 4.97V from about 4.90v and noticed a change.

I might wait till this thing is bone dry of gas and then adjust it so I have just under empty on the gauge using the CVR. IIRC I have set the fuel gauge sender in the Tanks Inc tank to be around that mark but it's not totally accurate.