brown engine coolant

serco

Hey,
I replaced the coolant thermostat in my MK4 Golf over the weekend to fix the problem of the engine warning light being on (turns out this wasnt the problem as the light came back on!).

Anyway, i also replaced the coolant with new pink stuff and all seemed fine. i drove it for around 15 mins or so and checked the coolant and it has turned brown, anyone have any idea why this happenned??

it was always pink before i wet near it.......the coolant problem aside, any ideas why the engine warning light might be illuminating now??

thanks

daedalus2097

Hard to know why the light might be on... Get someone with a VAG-Com setup to plug their computer into your car and check the output of the ECU... Could be anything really. Why did you think it was the thermostat? On the coolant thing, not so sure but maybe draining and refilling it disturbed some rust or corrosion inside the system which is now in the fluid, discolouring it.

serco

I had it over with a mechanic a while ago and he plugged the diagnostic thing into it and it said that the temp of the engine was -33 deg or something odd like that, so he said that it was more than likely the thermostat. so i changed it myself, seemed like an easy enough job.

i think i'll leave it in for a mechanic to take a look at it; i thought the same thing about the coolant colour, maybe rust from the engine or something.

thanks

daedalus2097

The temperature's not read by the thermostat, there's a separate sensor for engine temp, and a broken sensor or wire to the sensor will likely read very low. the thermostat only redirects the fluid to the radiator when it's hot and isn't directly linked to the management system, so I'd say it didn't need changing. I don't know where the temp sensor is in the Mk 4, but it's usually very easily changed. Find it and check the cable near it too in case it's just the wire that's the problem.

crosstownk

If G11(blue) and G12(pink) coolants are mixed it results in a brown mixture. Was the new coolant you added genuine VW stuff?

serco

originally it was pink, when i changed the thermostat and flushed the coolant out i only had blue stuff so i put that in. when i found out that i should onlt use pink coolant (the next day), i got pink coolant and after flushing out the system again i put the pink stuff in. i suppose its possible that there was a little blue coolant left in there.

it wasnt proper VW stuff, just coolant from halfords. its all i could find on a sunday afternoon....

its in with a mechanic at the moment so hopefully he'll sort it.

thanks guys

Mr.Diagnostic

crosstownk wrote:

If G11(blue) and G12(pink) coolants are mixed it results in a brown mixture. Was the new coolant you added genuine VW stuff?

I concur Also in extreme cases this can cause the viscosity of the coolant to change and lead to overheating problems. That needs to be sorted asap.

-33 is the default temp shown in live data on these when the coolant temp semsor is open circuit. The sensor itself is a very common failure and is both cheap and easy to replace.

crosstownk

serco wrote:

it wasnt proper VW stuff, just coolant from halfords. its all i could find on a sunday afternoon...

For the sake of peace of mind I'd be inclined to buy VW coolant - it's not that expensive. But being a Sunday you hadn't really any other option. If you do use the Halfords stuff, be sure it is compatible with VW G12.

serco

thanks guys, got it sorted by the mechanic. temperature sensor was replaced and the warning light has now gone off. Also got him to drain the coolant and put new stuff in. Fingers crossed it will be grand now, cheers