Sun Temp Gauge Technical Help
 

Looking for a bit of troubleshooting guidance on my Sun blueline temp gauge.

Took the car apart in fall for an engine freshening. Gauge worked good then (reasonably accurate) with what I felt was an original sending unit.

Fast forward to this week. I get the car running, but the gauge is DOA. I have power going to the gauge, and the wire running from the gauge to the sender has continuity with no resistance of sort.

In short, are the gauges that fickle? I noticed the engine builder coated the sender in teflon paste. The sender measures about 13 ohms from base to terminal at room temp (63 degrees).

Thanks,
Tim

The sender may not be grounding with too much paste on the threads. With the engine warm, hold a screw driver against the body and touch the cylinder head, Have Tracy watch the gauge for movement.

Also, if you quickly ground the sender wire with the ignition on the gauge needle should flicker.

Jason

There is power going into the gauge, but nothing coming out going to the sender. I checked for power going to the sender first of all (nothing) and then again at the output on the back of the gauge.

I then took it a step further to check for resistance in the wire going from the back of the gauge to the sender, and it's perfect.

The wire going to the sensor is ground only. As the sensor heats up, it gradually opens the path to ground causing the gauge to display the current coolant temp.

That sensor is the same as a fuel level gauge, it varies the ohms/volts allowed thru it for the gauge to read. The wire has to supply the power to do that. If the wire out of the gauge is dead, there is another issue. Hopefully, the wire didn't get grounded with ignition live during the engine bay cleaning and shorted the gauge out. Is there an in-line fuse that may have blown ??

There is not any power at the terminal coming out of the gauge. Something in the gauge is amiss. I'll pull it apart and investigate.

Did you try grounding the sender wire to see if there was movement on the gauge needle?

Thanks,

Jason

So is this correct?

Yep, I’ll break down the diagnosis,
1. Ignition On, using a test light connected to ground, probe the battery terminal at the back of the gauge. Test light should light up. If not, check fuse. If fuse good, check wire.
2. If you have battery at the gauge, ignition On, find a GOOD ground and jump to the sensor terminal at the back of the gauge. Gauge needle should sweep to its limit. If it does, gauge is good, move to step 3. If it does not sweep, replace gauge.
3 Ignition On, Again, using a GOOD ground, disconnect the sensor and jump from ground to the sensor wire terminal. If the gauge pegs again, sensor wire is good, go to step 4. If it does not, you have an open circuit in the sensor wire between the gauge and sensor.
4. Using a volt ohm meter, check for continuity between the body of the sensor(not the center terminal) and the intake manifold, you should have continuity, if you do, the sensor is bad. If you don’t have continuity, remove sensor and clean excess gook from threads, reseal and reinstall.

Strangely, I did check the gauge again for power where it comes out of the gauge, but when I ground the power lead going to the sender, it sweeps the gauge.

One of two scenarios.
1. I do not know how to properly use a test light.
2. The Sun gauge works a bit differently than stock arrangements.

On the bright side, the gauge appears to be good. The downside is the sender for these is tough to find.

At any rate, the problem is solved for now. Thanks to everyone who took the time and effort.

Tim

Sounds like the gauge doesn't send current until it senses a ground. I think you are back to the sender not grounding in the head. You went from cast to aluminum too. The head should be well grounded thru the head bolts, but never say never if the builder put sealant on those bolts too.

There’s a guy on EBay who reproduces those senders. He must know a fair amount about that particular gauge to make the senders no one else makes . Maybe send a message and ask for some pointers on testing . Is there someone close by you w a gauge you could wire in and test to see if it acts the same?

If you were concerned it was the sender not grounding just wrap a wire around the threads to the ground on the battery and see what it does. That should answer that question fairly quickly

I have a sender on the way from him. I should see it mid this coming week.