Temperature gauge

Not sure how to fix yours, someone else should chime in but if you want an electronic solution to monitor the engine and tranny you can get that from this company, with multiple sensors for the cylinder head, might I suggest #3 cylinder if you have the stock cooler and on the tranny.

https://engineguard.com.au

@Adrian R. posted:

My temperature gauge jumps up and down and on cold start its past the middle on the gauge.  Has anyone had a similar problem and what did you do to fix on the picture here are the only wire that I think might go to the gauge but I'm not sure

Has it always done this or did it just start? Is you car new? Did you recently change any wiring?

Someone smarter than me will no doubt weigh in but off the top of my head I would suspect you either have the wrong sending unit for your gauge or you lost a ground somewhere.

Does your fuel gauge work OK? Idiot lights?

More importantly: how is the ground strap from the engine to the chassis and/or the gauge grounds.

It's always done it since I had it.  I haven't changed any wiring fuel gauge works. Where is the ground strap from engine to chassis located on a 90s vintage speedster?

I’ll let a Speedster owner respond to the engine ground. On my Spyder, it goes from one of the starter motor bolts to the chassis tube. On an OEM VW, I think it goes from the starter to the body.

If it’s something it’s always done, as opposed to something that just cropped up, I’d suspect you have a mismatch between gauge and sender. Your pic looks like an OEM VW sender. Do you have the typical Brazilian VDO replica gauges?

If your gas gauge works and the idiot lights work, it’s likely not the ground on the gauge itself.

Engine ground is easy enough to check. Start your car and clamp a jumper cable from your engine to your pan somewhere. If your gauge drops down to normal range, bob’s your uncle.

The fuel gauge also moves around when I'm driving too

I don't think the gauges are VDO and just turning the key on with out engine running the temp needle jumps pass the middle

Have you checked your engine ground?  If that’s not it I would suspect you have the wrong sending unit.
Its “normal” for the fuel gauge to bounce around a bit. There’s a fix for it if it bothers you.

I assume you have Chinese knockoffs, even though most Chinese gauges I’ve seen have larger/flatter indicator light lenses.  This is what the Brazilian repros look like  the say VDO (because they are VDO Brazil) they also have pointed pointer centers vs the flat ones like your gauges  

Do you know how to check a sending unit for ohm load?

I ran a new ground cable from the engine case to the chassis.  How can I find out if I got the wrong unit or get the correct one and no I don't know how to check the ohm load.?

What happens if you unplug the wire from the sender?

With the engine off  key on and unplugging it the temp gauge does the same thing as if it was plugged in so I unplugged the other one sensor cable just to make sure I unplugged the correct one and a red light came on on the right side of rpm gauge

Have you tried swapping the two wires?

Im a little confused. According to my understanding, unplugging the temp wire should either leave the gauge at zero or top it out.

What happens when you drive the car until it’s up to operating temperature?

Perhaps it’s time to call an expert at Hollywood or Palo Alto Speedometer.

No but I will try that.  When I drive it shoes the same thing

Ok, so second wire/red light is the oil pressure warning light.

The first(temperature) wire when unplugged, ignition on should peg the gauge at the lower extreme. Plugged in, as the temperature increases, resistance goes down toward zero. It may not reach zero, but it should decrease as the engine warms. If you hook up one lead of an ohmmeter to the sender contact and the other ohmmeter lead to ground this should be easy to track.

250 or 300 degree F VDO gauges have something around 300 ohms at the cooler end, closer to zero at the warm end.

If the gauge is getting good power and ground, like Dave said, unplugging the sender should read cold. Conversely, grounding the sender lead should give you hot temps.

I found some info on TheSamba.

There are two VDO sending units. One with a 244-30 range and one with a 1240-210.

But two things are beyond my pay grade: The gauge not registering any change in temp as the motor heats up, and not topping out or dropping off with the sender unplugged  

I don’t think the wrong sending unit would manifest in either of those scenarios.

After wrapping my head around it a bit more I’m guessing that if the gauge needed a 1200-210 ohm sending unit and it had a 244-30 one, reading 240 ohms would give the gauge a reading.

But once again, that doesn’t explain the wired/unwired issue.

It's probably the gauge, but all the steps I gave will help determine that.

Thank you for all the help it ended up being the gauge that's goin bad. Time to try to find a set of gauges any recommendations?  On another note at idle where should the rpms be at.   Mine are around 1500 I had carbs rebuilt with the throttle bodies too so I'm trying to tune it and when I drive I get a bit of pop and studder between 3rd and 4th gear.

There is absolutely no reason for idle to be above 1000 rpm hot. I prefer 900-950 hot as that way it will idle cold, but slow until it warms up.

@Adrian R. posted:

Thank you for all the help it ended up being the gauge that's goin bad. Time to try to find a set of gauges any recommendations?  On another note at idle where should the rpms be at.   Mine are around 1500 I had carbs rebuilt with the throttle bodies too so I'm trying to tune it and when I drive I get a bit of pop and studder between 3rd and 4th gear.

You might want to call PAS or Hollywood and see if they can simply replace the temp gauge in your combo gauge. They can do it with some. And you end up with a real VDO part in your gauge.

All the builders sell gauge sets, as does Stoddard and Sierra Madre, but that’s an expensive way to solve your problem.