@Marshall. I can’t comment on the gauge set make, but I do have a question or two that may help diagnose the problem.
- do you get any movement from the oil temp needle when you power the car? You should see something... though it may be minimal... If not, you may want to pull the gauge ( a simple push from behind) and check/ clean all the connections. Something may have come loose/ or is dirty. If the other elements in that gauge are working properly it’s probably not the ground. Look for a bright green cable that matches the color of the cable on the sender wiring... that should be connected to your oil sender gauge mechanism.
Pictured in your last post you have the oil temp sending unit ( top of the T), and oil pressure switch ( bottom of the T).
- The Oil Pressure Switch operates the oil pressure indicator bulb on the speedometer. The switch looks to be the standard 10x1.0mm threaded one and operates at roughly 3 PSI. Meaning that if the oil pressure indicator light is on, your engine has less than 3 PSI of oil pressure at the switch
- the oil temp sending unit green cable should be run directly to your temp gauge. You should see the same colored green cable behind your gauge. That’s the connection I would check. I would also check for continuity between the oil sending usniy and the gauge.
- the T is commonly used on VS builds to run both of these senders.
oil senders are simple mechanisms that don’t fail often... But they can fail. There is a chance you have a loose/ dirty connection at the gauge or even at the sender ( corrosion can really mess with your wiring), or your Chinese/ Brazilian gauge has pooped out, Check continuity and connections before buying a new sender. I can send you some how- to instructions to check continuity if you need help.
- by the looks of it, you likely have the OEM VW sender part #049 919 501 - oil temp sender, short - 10mm, 0-120c range used for mid-70s to mid-90s VW stuff. And commonly used now for small aircooled engines. Also VDO version of this one installed in the car, part number 323-088. https://www.jbugs.com/product/V323088.html
i had a similar problem years back... it turned out I had a loose cable ( the first time). Then, eventually the Chinese gauge failed... and I sent my gauges to Palo Alto Speedometer and VDO guts were installed replacing the cheap Chinese made ones.
Hope this helps.