Can any solve the mystery of the faulty temp gauge

I do not understand why instead of testing at a known temp (boiling water) you'd rather keep randomly replacing senders.
Come on, one of you fellows - how hard is it to wrap some wire round it for an earth and dip in a pan of recently boiled water? You've no doubt got a cooker and pan right there in the van!

 

This ^^^
Elimination is the key , it's quite a simple set up if everything works as it should .

Mine is a dipstick sender but came complete in a blister pack from VDO .
I wouldn't put it past some of the dealers out there having a few old gauges they can't sell buying a bunch of dipsticks and selling them as a set ....
Was the OP a definite factory sealed pukka VDO set or loose in a box perhaps ??

Sent from my SM-G960F using Tapatalk

 

Ha the other guys said he has done it and it gave a perfect reading buddy

 

Yer I have tried 3 senders and 2 gauges the chances of them being defective are slim to 0...

 

Interesting that's what would probably happen if I had a bad earth I imagine

 

Actually he said he heated it up with a hot air gun so I don't see how he could judge it's accuracy other than it went higher than the 55 degs.

 

Unless they all came from JK's mismatched stock in which case you'd expect nothing else.

 

I am trying to help.

 

Is that bloody gauge working yet ?

 

If the gauge doesn't go to max, are you sure the positive feed for the gauge is connected to 12 volts and not the output of the fuel gauge stabilizer.


A max reading on a VDO gauge is what you get if the sender lead is shorted to earth.. as I said with the dipstick sender that's a 50% chance if you just slap the wire from the gauge on one of the pins on the sender and earth to the other.

If you go through a lot of gauges and senders all nominally working from the same set of gauge and sender when sent to you, you probably have a permanent installation wiring mistake that is nothing to do with the product.

 

Not hard at all! I used a heat gun remotely ( as stated in my post !) also boiling water with an earth wire . The gauge worked fine at the expected temperature. Put the sender back in the sump and only went up to about 55….This driving for over 200 miles in Southern Spain at outside temp of 30 +.
So …
1. I don’t think the sender was faulty ( JK sent me a replacement that behaved the same)
2. Don’t think the gauge is faulty as it worked fine when sender heated up remotely.

3. The only logical explanations ( but open to others )being 1. as @mikedjames has suggested ie. The sender is not earthing properly ,perhaps due to paint or possibly I may have used ptfe ( thoughI don’t think I did) 2. My oil doesn’t heat beyond 55 degrees or 3. The location of the sender in the sump is totally inefficient.
All may come clear when I get the dipstick sender from Heritage which they say is EU made as opposed to JK’s Chinese one

 

Always happy to check but have probably checked it a dozen times.
This doesn’t explain why the sender when heated remotely by the gun crept up to over 100 from memory before I stopped and crept up to virtually the same reading I had taken of hot water via a separate thermometer when immersed.
Ps. I presume that the wiring must be correct as when I heated the sender remotely I used the same wire that went to the sender when sump mounted, only the earth was changed by wrapping wire around the sender thread and iirc to a door hinge.

 

Waiting for the postman

 

Did you say you had fitted a nice new sump plate ...I did the same my one was a silver csp expensive one I thought it was aluminium ...but thinking about its probably sprayed silver ...if your due a oil change it may be worth taking off the paint around the sender and seeing if that works...I have just changed my oil so will have to wait before I try it...it may be worth giving it one last try before you switch to the dipstick sender that look a bit crap in the engine bay....let me know if it works

 

Thanks for the replys guys

 

No I had the CSP/scat ? One but this meant the sender protruded with little protection so swapped this for an angled one which has cooling fins on it ( could this have an effect ?)
I’ll post the outcome when the dipstick is fitted , hopefully Monday

 

https://www.volkszone.com/threads/brand-new-beetle-roof-rack-csp-sump-plate.1600046/ is it this one I also have the angled one with the cooling fins made by csp....we may have found the problem

 

Just checked does not seem like you can buy them anymore ...

 

The dipstick may not be compatible with the gauge, although I would expect the needle to move a lot further than 50C even if the senders arent compatible.

The sump senders read maybe at maximum 10 degrees cooler than the dipstick I seem to remember, the tip of the sender is sitting in the oil.

Get out the ohm meter and measure the resistance from the existing sender body to the engine block. Should read the same as touching the meter probes together..
Or power up the ignition and check theres voltage on the sender tag and no voltage on the sender body relative to the engine block.

 

Just checked jk selling the same gauge with either dipstick or sump plug so assume it will work