Cooling "Issues"?

[MattVR6 10]

Hi All,

 

Successfully got my car in for a service yesterday at my small independent mechanic. I supplied all my own fluids as per my previous thread. Mechanic contacted me last night with a few issues/questions to do with cooling.

 

After the service he took it for a road test (as he always does) and didn't notice any unusual temps on the dashboard. When back at the workshop, the header tank seemed very very hot, the coolant hoses were hot-ish but the lower radiator pipe was warm at best. He said he gave the lower pipe a few squeezes and then it started to flow hot. All hoses have been replaced 6000 miles ago for samco items and the radiator looks in good nick (although not sure when it was replaced) so i'm guessing a blockage is unlikely.

Also the aux water pump no longer runs after the ignition has been turned off.

 

The main water pump is 3 years old and not leaking. During the service, the coolant was flushed and pressure tested.

 

So what do you reckon?

 

I have done some research and it must be either FCM, thermostat or coolant temp sensor. Any guesses as to what could be the likely culprit. How likely is it that the car may be overheating but the temp gauge says otherwise?

 

When I get the car back tonight, I will run some tests to see if my fans work at all 3 stages etc.

 

Also for the road test, he mistakenly put in his own long life coolant. He has since refrained and put in fresh G12 which I supplied. Could this have caused any issues?

 

Cheers, Matt

[dr_mat 0]

Sounds more like an air lock to me.

 

The electric water pump doesn't run after ignition-off full time, only if the engine is up to temperature (as recorded in the top hose).

[Jim Bowen 1]

The dash gauge is a bit of an iffy reading, replaced all of my cooling system and still the gauge reads low, you can check the actual temp the ECU is getting with VCDS software (i've got that if you haven't, could check yours if you are popping over to collect the switch)

[MattVR6 10]

Yeah I thought an air lock also as after the test drive (purchase day) the coolant was very low. I topped it up before I drove back home, knowing i would be getting it flushed fully within a week. Occasionally there was a bouncing idle while stopped after driving if the car was up to temp, but would go after a few seconds. This should all be fixed with the service.

Ah yeah I have read about that, above 90-93 deg or something the water pump runs? I need to test that, give it a good run then switch off and see if the pump runs on.

Also Jim if I do pop over then it would be a bit silly not to!!

 

I still haven't got the car back from the service so I reckon this thread may have been a bit premature. Picking back up tonight so will drive for a few days and update this thread!

 

Thanks for the replies chaps!

[MattVR6 10]

UPDATE:

 

"Issue" is now ISSUE.

 

Drove the car back from the garage after my mechanic again saying he was worries about the cooling system, I said I would look into it.

 

Driving back the car was faultless, no more bouncing idle (air pocket) and temps were all good.

 

As I got back home and parked.....oh dear. The header tanks was hissing and ****ing water everywhere. Obviously a lot of pressure and very hot! However, top rad hose and the engine top was only hot-ish. Both rad fans remained spinning (ignition off) for 5 mins or so. After they had stopped spinning I felt the radiator and it wasn't even warm.

 

I am now worried

 

I reckon this is a faulty water pump due to a lack of water flow?

 

After draining the garages coolant and before putting in the G12, mechanic man said he had the top and bottom rad hoses off, flushing water straight through the rad, no blockages.

 

How can I check that the water pump is faulty?

 

What else may the issue be?

 

Please help! Don't want to damage my Corrado!

 

Matt

Edited November 25, 2015 by MattVR6

[Will.I.Dub 11]

Thermostat?

[Gti_Jamo 10]

It's hasn't lost its rubber 'O' ring from the inside the cap for the header tank by any chance? As that would give the illusion of overheating. Also different types of coolant if mixed, can turn into a sludge that can cause blockages.

[VAG-hag 0]

Thermostat?

 

That would be my first check

[MattVR6 10]

Roger that. Will check both these tomorrow morning and will let you know

[Wesleyvr6 10]

Id say thermostat too, take it out and test in a pan of hot water.

[MattVR6 10]

Hi all,

 

Ok the o-ring on the header tank is intact, but I was doing a lot of research last night and I am 99.9% sure it's the thermostat. I do not have a garage or driveway but I do live on a very quiet road, so minor work can be done to the car. Can the thermostat be removed to be tested without draining the coolant? Would rather test before a new one is purchased if found to be faulty. If not then I will have to purchase a thermostat and housing (the cover is present and intact) and drive to the closest garage (before the car gets too warm) and get them to fix it. Can I then request the garage to keep the old coolant....seeing as it has only done about 4 miles? Or will more be needed? I had G12 put in before.

[VAG-hag 0]

Coolant will be largely drained. No reason not to keep the old stuff I suppose but it really doesn't add much cost.

It needs removing to check it.

[seanl82 23]

You shouldn't need to drain too much to be fair as the stat is quite high up in the system. As previously suggested, stat can be tested using a pan of water brought to the boil. Should open up at 87 degrees or there abouts. They are often completely goosed though so its obvious upon removal that its had it.

[MattVR6 10]

Hi all,

 

Next week (when it arrives) I will be replacing my thermostat, housing and seals etc. When I transfer the 3 sensors to the new housing, is there any way to test them off of the car, as it would be a bit of a missed opportunity to replace them otherwise.

 

Also what is meant by a 2/3 stage fan setup? Is that the number of fans on the radiator (mine has 2) or the number of speeds the fans can spin at?

 

Lastly, my thermostat housing has the brown a/c cutoff sensor.....not a plug? I didn't think my vehicle has air conditioning. Thoughts? Where would the a/c pump be housed if it was present. It would be a lovely addition =)

[MattVR6 10]

https://www.vwheritage.com/shop/021121117A/thermostat-housing-2-8-aes-t4-1-96-06-03/

 

Also this is the thermostat housing I have purchased, do I also need to purchase the outlet flanges as well? As seen here:

 

http://www.vr6oc.com/e107_files/public/1298474753_8829_FT424747_thermostat.jpg

 

Thanks

[Roger Blassberg 0]

in your situation I would replace all the cooling system plastic parts including the transverse pipe and associated o rings. There is a strange shaped one in the thermostat housing.That way you can forget them for years to come. Be careful if you try to undo the bolts that hold down the elbow on the top of the radiator because they go into captive nuts cast into the top of the matrix. If the nuts start to turn, the radiator top will crack and you will need a new complete radiator.

Best wishes

RB

[AngusL 10]

Matt - additionally fit a manual fan override switch inside the car. wire to sensor no 8 in the second image you showed. No relays needed as they are in the FCU already and it doesn't upset the existing wiring. I did this to mine and it has saved me a few times. To test this just switch on the ignition and bridge the two wires to sensor 8 and you will see the fan cuts in on full power - On demand cooling. It is a really easy back up fix.