Coolant leak Thermostat/Temp sensor

[Rich D]

Hello, I've got a small coolant leak at or near the temperature sensor that sits by the thermostat. It looks quite difficult to remove the sensor. Has anyone successfully used something like radweld in a 1.9 DG engine?

1990 1.9 watercooled

[kentishvanman]

I have used it ages ago. Cannot remember the problem or even if it solved the problem but it did not do any harm. Try it and see what happens.
I don't remember the sensor being that difficult to take out/change. Not a lot of free space but 'do able'.

[Mocki]

Removing the sender is very easy from the plastic thermostat housing , even easier from the metal ones .
Don’t feck about with rad weld, all you will do is cause yourself overheating issues in the future when it’s clogged all the tiny pipes up in the radiator and heater matrix . It’s a last ditch get you home last resort imho

Don’t bodge a day repair

[Robsey]

As you appear to have a later van, you will have the plastic distribution tower with both sensors mounted in it.

The sensors are retained by a plastic clip, similar to a circlip.
Just carefully lever this out, and the sensor will pull out.
Between the thermostat housing / tower body and the sender there will be a rubber 'O' ring.
Chances are that this has compressed, shrunk or cracked with age.

Ideal plan would be to replace the 'O' ring and refit the sensor.

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As said above, these vans can be susceptible to overheating due to the ad-hoc approach VW used to jump from air-cooled to water-cooled.
Therefore putting anything in the fluid such as rad-weld could potentially clog up the thinner cooling passages of the engine.

So only use it, if you have no other choice.

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One possible option would be to put the finest possible bead of plumbers high-temperature sealant around the 'O' ring where it bears upon the sensor body.
Just enough to build-up the seal / fill any cracks.

Too much and you risk bits breaking off and clogging the cooling system.

The reason I mention plumbers silicon sealant and not your B&Q diy stuff, is because professional grade can be rated upto 300°C. So will not deteriorate with engine heat. (Read the label to be sure if you get some).
Great for sealing exhaust joints too.

But again - the IDEAL solution is to fit a fresh 'O' ring.
The plastic C clip will be a bit stiffer to fit because the 'O' ring should be a tight fit under the sensor.

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For those with the early water pump and thermostat housing, the sensor is an M10x1mm screw-in item.

A pig to get at because it is near the waterpump pulley, engine carrier cradle and water pipes.
The repair in this case is a new copper washer.
Copper, not brass. Copper is softer and will conform better to the contact faces of the thermostat housing and the sensor body.

[Rich D]

Thank you all for your replies. I reckon the main messages are . . . no radweld in this case, and, try to get the sensor out and replace the seal. Bit of a bugger to get to.

Is this the sensor that reads out on the cab temp gauge or some other function?

Cheers, Rich D.

DG 1.9 water cooled, Holdsworth conversion (Reading), 5 speed, 1990 ish, moderately tidy in most respects.

[Robsey]

As you have a carburettor engine, there should only be one sender - this will be for the temperature gauge.

Only the injection engines would have a second sensor for the ECU.

[Rich D]

Excellent. Last question. When I take the sensor out would I expect coolant to pour out?

DG 1.9 water cooled, Holdsworth conversion (Reading), 5 speed, 1990 ish, moderately tidy in most respects.

[Robsey]

Some coolant will leak out due to some pipes being above the height of the sender.

All coolant below the sender will stay in the pipes and engine.

[Mocki]

As you have a carburettor engine, there should only be one sender - this will be for the temperature gauge.

Only the injection engines would have a second sensor for the ECU.

Not true , there are two senders , well the temp sender and the switch for the carb heater .
The temp sender is the one facing the front of the van the switch for the carb heater is the one facing the rear wheel .
They look the same , they are not the same .

You will loose coolant when you change the sender , buy a new sender , which will come with anew o ring , have the new one ready , and swap fast , do it when the engine hasn’t been started and do not open the header tank cap

The reason i mentioned the metal thermostat housing is because syncros have a metal thermostat housing so age didnt tell which you had

[Robsey]

Ooh you learn something new every day.

For some stupid reason, I was still thinking that the carb pre-heater switch was on the cross engine pipe.

This is where I say d'oh!!
Cross engine pipe is early cooling only.
Not on your later set-up.
Oopsies

[Rich D]

Brilliant, top tips thank you.