I don't know if the gauge is defective or if maby its a bad ground? I installed this last summer and started having this problem about 6 months ago and now its happening more frequently. The gauge does properly display the coolant temp once the car is fully warmed up, but during the warmup process, it seems that the gauge's needle is bouncing around like crazy ranging anywhere from 0 degrees to 300 degrees uncontrollably.

I thought this would be a grounding problem, so I relocated the ground to a better location and still the same problem. My ground wire I had to modify it to get it to work, so the contact area is very small and I thought that might also be the problem so im trying that next, but has anyone ever had a problem to where their aftermarket water temp gauge needle bounces around like crazy?

 

It has to be bad wiring. It may be that your sender is not wired properly either.

 

I've seen it several times on different cars. I bet he's got an Autometer gauge.

 

Yeah I had this same problem with my prosport gauges. Eventually all the gauges had the same error. I contacted tech support and they said it was bad senders and they would warranty.
On the other hand a buddy of mine has some high quality electronic gauges that are a Japanese brand, I think it was Apexi or HKS not sure, but even after 10 years they still function for the most part. I think the EGT flickers sometimes, but it's not bad for 10 years.

 

The sender could've gone bad, the gauge itself won't bounce around, it's most likely reacting to bad/noisy signal from the sender.

 

I read on another forum that it may be a bad ground, so I cut off my questionable modified small ground wire and installed a much larger ground. Im afraid if that doesn't work you guys are probably right the sender may be slowly failing. If thats the case ill have to buy another gauge/sender assy.

Everything worked out for about 6 months, gauge worked exactly like it should, until recently. Kinda annoys me, because when the needle is going wild, idk what my engine temps are and it feels like im driving blind folded :-/

 

Some senders need to be grounded. You should check on that before replacing everything.

 

I redid the ground for my temp sender and installed a larger ground and put it in a cleaner location. That didnt make a difference.

UPDATE: I have confirmed that the erratic movement of the needle only happens as the car warms up. Once fully warm, everything measures perfectly. Even if I just finished driving it and let it sit for about 30 min and drive again, it would not have any problems measuring temperature, because the sender is still heatsoaked. The only time it has the problem is during the initial warm of the day.

What do yo guys think, is there anything else that can be done, or is this water temp sender on it's way out?

 

you might wanna make sure the system is bled. the BMW E30's get air pockets, and the needle jumps around because its at the top, and its going in and out of water.

probably not it, but its free and easy

 

Where is you sender located? Sounds like it may not be in constant flow of water when cold.

 

I think it's just the sender, I don't think you can do anything. Just live with it or get a new sender.

 

The sender is located behind the UIM on the throttle body coolant hose ( the one that connects the throttle body to the engine block.) I dont think its a coolant issue, because I havent done anything with the coolant in the past year besides check the level every now and then, and this problem is something thats been going on for a while but progressively getting worse. The way the gauge needle is bouncing around so fast is most definitely an electrical problem, so unfortunately i agree with godsquakmandrake :-/

Does anybody know of any good quality water temp gauges/senders from reputable manufacturers I can start researching

 

i had the same problem when i wired it up the same area as yours,

just use the rad hose.

 

mine is in the throttle body hose. No bouncing issues.

 

Ok guys I did something extremely experimental and I will explain. Because my water temp gauge works fine once the engine is fully warmed up, but only has the problem with the erratic needle while cold, I read that it's because theres too much resistance with the engine cold. Apparently as it warms up and gets hot, the resistance goes down. Knowing this, I decided to cut the water temp sender ground wire, and connect 3 grounds to it in parallel. This in theory will open up the flow of current on the ground side of the circuit,reducing resistance, and will dampen the erratic electrical pulses during warmup, which are causing the gauge to go haywire.

Along with twisting/soldering three new grounds, I also cleaned the ground bolts thoroughly, and sanded the surface it was being grounded to, to ensure a good ground for all three. Ever since completing the job, I have cold started the car 3 times all the way to full warm up, and the gauge has worked perfectly everytime. I will need to drive the car a lot more to ensure the problem is actually gone, so I will update in a month.

 

Where are you grounding it? Through the engine block? If you ground it directly to the negative terminal or any ground point you shouldn't have this problem. But it's good to hear that you found out what it is.

 

I grounded them to three 10 mm bolts on the firewall that are holding the brake vacuum hoses together, they screw directly into the frame. I really dont know if this is a permanent solution or not, because I have searched and never heard of anybody doing this before, but being thats it's free it's worth a shot

 

Its only been a few days, but I have not seen the problem come back. Honestly i'm probably guessing I'm having this problem because the gauge is cheap. If I had gotten something like a Defi, I wouldn't be having this problem, but never the less looks like adding more grounds in parallel to the exsisting water temp sender ground was the solution to the bouncy needle, so hopefully this helps someone else in the future