Club 80-90 Forums

I have a newish temp sender that appears to show a higher temp than the old one (when it was working).

It now sits noticeably right of centre. 

My son has one of those new fangled thermometers that you point at things. 

So...in order to fully understand what temp the van is running at:

Where should we point it? Rad? Thermostat housing? Anywhere else?

What range of temps should we be seeing with a thoroughly hot engine?

Last summer a run down the motorway followed by standing traffic would make the small fan come on. This winter stuck for over half an hour on the M1 the gauge went to 3/4s but the little fan did not come on (no lights etc). My son chickened out and flicked the chicken switch and the big fan brought it back down quickly

I'm conscious that the fan is controlled by the switch in the rad and the gauge by the sensor in the thermostat housing.

I think it is fine but just want to double check.

It sounds fine to me, there's a fair bit of tolerance in the sensors and these gauges do like to read on the high side, to the point that gowesty etc sell a little trimmer resistor to put in line and recalibrate the needle to read in the middle.

This is the reading I took on mine when I was having similar doubts. I took this while the engine was up to temp and showing about 2/3rds on the dial.

Measure at several places, then compare the values.

The intake side of the thermostat should show the temp of the coolant inside the engine. The 025121113F thermostat for the petrol engines should be a 87C one, which means it starts to open around that temp.
The fan switch in you DG should be a 251959481K which should switch first 1st stage on at 87 off at 76C, 2nd stage on at 93 off at 82C according to part catalogs (repair manual says 1st stage on 89-94C, off 81c, 2nd stage on 95-100C, off 87C)

I would say on idle, around 90C at the thermostat housing with a regularly in and out switching fan first stage would be a perfectly working coolant system and the engine is at operating temp.

What the gauge shows is a value depending to the resistance to ground through the sender. Higher the resistance, lower the temp is.
So if you have bad contacts or off voltages it can show off values. And the senders are not equal in quality.
Here is a good thread about testing the temp gauge:
https://www.thesamba.com/vw/forum/viewt ... p?t=464113

Thanks for the help, I'll give it a go just to set my mind at rest.

Turns out that our son has a couple of IR thermometers and an IR camera which could be fun.

Over the last couple of years I reckon I've got the message across that he can do what he likes with the van when he borrows it but if it overheats and blows a seal etc it is 100% his problem!

You need to be aware that an ir thermometer only measures radiated ir, which differs depending on material and it's colour. Black aluminium will read higher than polished silver aluminium. A black rubber hose is likely to read much lower. So only compare like with like, or you will become very confused!
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