Not getting up to temperature

[islandboy]

1987 1.9DG WBX Petrol
Just lately, temperature guage is taking forever ( 20 miles plus) to get anywhere near my normal indicator position. Engine is starting and running fine. Have a peristent weep from coolant distributor block and always topped up water tank behind number plate and temp guage showed fine. Van is going in to garage next week to have new distributor block installed.

Have I got air in the system or is the thermostat on the way out ?

Many thanks

 

[Robsey]

For 95% of vehicles, taking a long time to heat up points towards a thermostat that has failed in the open position.

[silverbullet]

The temp gauge only tells you what it can "see" via the sender, which being a resistance device exposed to engine coolant is subject to
1. Earth return/high resistance faults.
2. Poor thermal conducion due to low coolant.

I would fix the known fault first (the leak) then bleed the system thoroughly before changing anything else.

Changing the thermostat will of course require re-bleeding afterwards.

[islandboy]

For 95% of vehicles, taking a long time to heat up points towards a thermostat that has failed in the open position.

Showing a bit of ignorance, do I need to drain off all the coolant system to replace the thermostat

[Robsey]

Not at all...
The less you drain down the better.

If changing the thermostat, you only need todrain down to the level of the thermostat joint, in the housing on the front left corner of the engine.

I would drain down fully, if I thought that the coolant was getting old and contaminated from protecting the engine for more than two years.

Otherwise, you are looking to burp the air out whilst topping up the coolant, rather than draining down.

Ensure that you use the correct coolant type for these VW engines.

With regard to the comments from Ian before.

In my experience...(but I am not a professional mechanic).

If the temperature gauge reaches the usual temperature but takes a while to get there.
Or the needle drops significantly if moving briskly then that hints at my suggestion.
Thermostat stuck in the open position.

If the gauge needle fluctuates by a significant amount or the air blown out varies between hot and cold, then that points to low coolant level and a lot of air in the system.

If the needle of the gauge does not reach the usual expected temperatures, even if stuck in traffic or idling for long periods, then that points towards sensor, earth, or wiring issues. Dirty or corroded terminals would drag the readings down.

[islandboy]

Thanks for that. Robsey, I'll give all electrics a clean up, presume I'm still ok for driving as long as coolant levels high

[Robsey]

As long as you keep plenty of fluid in there, you should be okay.

I am surprised that the header-tank fluid level switch has not been mentioned.

You should get a warning if the fluid level drops too low.
Temperature LED flashes regardless of gauge temperature value.
Assuming your relay No 42 or 43 is working too.