Temp gauge jumps to into the red

[soutie]

On my rebuild, I ran the 200 tdi engine on Sunday to charge the battery and to see if the temperature gauge was working, while sanding outside. I came back in to find the temperature gauge in the red. So switched off. Top hose was cold so suspected the thermostat. I changed the thermostat and tried again on Monday. This time I sat watching the gauge. It again jumped from the 40 degree point straight to 120 degrees. Switched off straight away. This time the top hose was hot for about 15cm and then cold. The gauge is a VDO gauge and sensor which was working 12 years ago before the rebuild.

Question, here is this the water pump not working, the gauge or sensor? Water pump belt is tight. Looking at the engine, there is now a water leak on the thermostat housing.

Hopefully have not cooked the head. Oil is clear with no trace of water.

If I do replace the water pump and retighten the thermostat housing should I use red gasket paste / some other gasket paste on the paper gasket or not?

[Retroanaconda]

How long did you run it for? And was it at idle?

[Bowie69]

I'd suggest either wiring, sender or gauge is at fault, there's no reason for an idling Tdi to suddenly jump into the red. 

[soutie]

It was at idle. On Sunday for about 10 minutes. On Monday for about 5.

[western]

Not long enough for a 200tdi to get up to working temp, gauge or wiring fault, check the gauge wires are not touching the U clamp 

[Sigi_H]

I always recommend using a IR Thermometer, to check what is really hot. In my eyes it is not.

 

 

[Ed Poore]

Bad earth's to the dash will cause the temperature gauge to read high, I've had this before.

The earth runs from battery to the chassis (there's a P clip holding the cable onto the chassis but it is on a bare piece of the cable so provides an earth), from there the end of the main earth is bolted to the transfer box. The dash is then earthed on a stud on the bulkhead in the engine bag (left hand side as you look from the front of the vehicle).

I had unreliable an temperature gauge and it was caused by a bad dash to chassis earth provided by that P clip.

[Snagger]

I think there are two suggestions above that seem most likely - a short in the wire from gauge to “sender” and a bad earth between gauge casing and bulkhead.  A gauge or sender failure are possible, but not that likely.

[Peaklander]

Just adding to the earth ideas, I’ve mentioned it before that on my 110 with 300TDi, there’s an earth point on the TBox near the front flange, right hand side. A problem here affected my binnacle gauges. 

[steve b]

1 hour ago, Peaklander said:

Just adding to the earth ideas, I’ve mentioned it before that on my 110 with 300TDi, there’s an earth point on the TBox near the front flange, right hand side. A problem here affected my binnacle gauges. 

check this first and then the BH earth stud, and get an IR thermometer , under £20 on ebay 

Steve

[soutie]

Thanks for all the replies. Will check this weekend.

[soutie]

I bought myself a IR thermometer and went to check it this afternoon. With the housing around the tempreture probe at 50 degrees the gauge read 120 degrees. I then cleaned up the spade terminal on probe and put a wire on it to the gauge and it still read the same. Taking off the positive and negative wires from the gauge and using my Sealey auto probe to provide voltage it the read 50 degrees. Looking at the wiring I found somebody had added in an earth wire in red with a double spade which I had connected to the positive terminal instead of the negative. This sorted and the gauge now works and reads correctly. Thanks for all the replies and suggestions. The IR thermometer really helped.

[Sigi_H]

Nice to read that. There are more interesting points for the IR like wheel hubs (bearings), gearboxes and diffs. It is good to know the normal temps.

 

[miketomcat]

Whilst it sounds like a wiring problem, I have had an impeller fall/snap off. Externally the pump looked and seemed to be fine but when I took it off the impeller fell out.

Mike