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Alright Guys,

Random issue today.

Half hours drive, half town, half motorway. When i arrive the aux rad drivers side was steaming and the area around it felt pretty hot.

Not blocked and i couldnt see any leakage. Car temp fine at the normal 90 deg, although as its only the aux maybe this wouldn't be affected any way?

Drove same route back, checked everything again (and when i came off the motorway at half way) and no issues at all, area not even particularly warm?

Car temps still fine so presume it hasnt ditched the coolant...
It's not a separate reservoir is it?!

Any ideas?
Seems strange to have a big temp difference for the exact same drive...

I would check the coolant level straight away as they can rot over time (it's the crud that kills) and you do not want to run out of coolant! I've heard of the pipe joints splitting / leaking too! I would guess that the auxiliary rads are thermostatic, so they will only "open" or be used when you've go the car hot and then close again.

Mid / Rear engine Porsches are notorious for this too. So much that it's actually a service item to do an inspection / clean out this debris ....

Was discussed here: viewtopic.php?t=88591

Coolant looks good...

I'd seen that thread, my radiators look clean and in good health.

Will keep an eye on it though.

Last thing i want is it to dump all the coolant and go bang!!!!

Strange that the same journey, in the same conditions wouldn't replicate the issue though, unless there was an air lock somewhere that's been fixed by driving. It's not moved in a week so maybe...


Cheers

Weird - unless you went through a deep puddle on the side of the rad? Or were driving in rain beforehand. I know the oil cooler on my Golf R sometimes picks up puddles and does this after a fast run in the rain.

I get the airlock, but perhaps the thermostat on the auxiliary cooler is yet to open fully and if it's empty, when it does, the coolant will drop.

I had similar on my 2 of my old B6 S4's -1 Avant, 1 Cab - where the thermostat seized shut, the main rad got too hot and the pressure/heat caused the aux rad connecting pipe and housing to split - the tell was some steam from the side of the bonnet and a slow drip of coolant. In both cases I was confident that coolant was not leaking fast enough to cause an issue but went straight to my dealer who sorted it under warranty.

Didn't have any issues with my B7 or B8, and my current B7 had its Aux rads replaced when I bought it last year.

Only thought is that the thermostat had only just opened before your stopped, leaving enough time to fill the aux rad with hot coolant, and if the steam was from the body of the rad rather then a forced exit from some split or hole, then it could have been moisture from the road that was evaporating of.

I would put either a mass of kitchen towel or a large rag under the front of the car overnight and look for coolant the next morning. Once something splits, it won't matter if its hot or cold to drip out, and any split to the hoses connecting to the aux rad should - in theory - be on the main rad side of the flow as that is where heat/pressure would build first.

Ah, thanks for the input.

Hadn't realised they weren't fully open all the time.

Could be either/or the puddle/wet road and just opened scenario, had been doing 70*ish then just a few mins slow driving aling wet roads to park up.
So it could have just opened on the motorway maybe, and then splashed.

Will see if i can detect any leakage under the car.

Thanks

That's similar to the classic 'schoolboy error' ! Thinking the radiator has developed leak just after starting the car from cold, when it is actually rain water or frost that has formed on the radiator fins, which 'steams' as it gets upto temperature.
Not going to say "been there - got the t' shirt", but have come close on older classic cars in the past.....

Just a random thought... it was mighty cold in places last week let’s hope the coolant had the correct antifreeze percentage?

wideboy - did you get any further with this?

All looks good, had a run out yesterday and no issues, no coolant leaks.

Must have just been a mis-timed puddle evaporating i think.

Excellent news!