A few weeks ago, I replaced the radiator on my girlfriends 8 valve gti. Since then we have had a few issues with the heater not being as hot as it should. I have fully bled the cooling system for a second time and also replaced the expansion tank black cap for a new VW blue one!! The heating seems better now and the gauge is getting up to half way, so the thermostat is definitely working! However, there still seems to be some minor coolant loss and it appears to be weeping from below the screw in temperature sensor on the bottom right of the radiator. I didn't replace this when the new radiator was fitted, just re-used the old one!! I have tried to tighten it a bit, but don't want to force it. I have also put some silicon type sealant around the gap between the threaded sensor and the radiator screw in bit? I don't want to tighten it any more!! I will leave the sealant overnight to cure and hopefully that may solve it? Any suggestions if it doesn't?? Alpenweiss2 p.s We have a 600 mile round trip to do in the Gti tomorrow!! Cheers Alpenweiss2
I don't remember them having one but its a longtime since I have had to change mine From what i remember they are copper seating faces just torqued up snug Don't overtighten it though! Some threadlock on the seating faces migth have been best approach when you had time to dry it out and refit
aye it's a copper or aluminum washer i would get a new one the vw p/n is N 0438083 the washer is 22mmx29mm it would be a 1 or less or some motorfactors may have that sort of thing if you take the old one in or give them the size
Cheers Mushy!! My temporary fix will have to do for our long trip from Kent to Lancaster and back!! Once we get back I will order a new washer from VW drain the coolant and redo the job properly! Cheers Alpenweiss2
Did you give the copper washer a rubdown with emery paper. Even better, would be to re-anneal it by heating it till glowing red (google 'annealing copper washers')
Somethings not quite right? Well we are currently travelling to Lancaster in the p*****g rain on the M6! Something is definately not right with the cooling system as the outside temperature is 5 degrees centigrade, yet even on the motorway at a steady 70mph the coolant temperature gauge is sat just below the centre?? The heater is set on full yet the air coming out is not that hot?? The car does have the bypass valve thingy fitted in fact we had it replaced about two years ago as the old one was blocked. The gauge seems low on the dash so maybe the new radiator is super efficient? The bottom rad pipe doen't get warm straight away, but only once the engine gets to a certain temp then the pipe gets nice and hot, so thermostat must be working? Maybe it is calibrated wrong? Any ideas? Alpenweiss2
Sounds fairly normal at this time of year... the engine isn't working hard at 70mph, and it's got loads of cold air blasting through the rad. I'd be surprised if the 'stat was fully open.
Hi MikeH The thing is, before the rad was replaced the engine got up to a decent temperature and the heater was toasty warm. Do you think it is worth getting a new thermostat from VW (16 + VAT) plus a new housing? Apparently the job to replace the thermostat is a bit of a pain? If we get a cold spell in January/February/March I would like to get this sorted before then. I may also remove the bypass valve and clean it out? Cheers Alpenweiss2
Any ideas on this guys n gals? Could the thermostat be faulty in some way or is it more likely to be the bypass valve getting blocked or not working correctly? Is it possible that the gauge sender is faulty? I am just worried that the engine is not running as hot as it should and thus this is impacting upon the way the engine runs and also fuel economy? The oil temperature indicated when cruising a 70MPH with a 5 degree outside temperature is around 90-92 degrees? The radiator bottom hose doesn't get warm straight away, but does get hot after a drive, which seems to indicate that the thermostat is opening? The mystery is that before the rad was replaced the heating was toasty warm and now it struggles?? Alpenweiss2
Oil temperature is OK which to me indicates that the cooling system is fine. When you changed the radiator did you get any sludge out of the system, did the radiator fan temperature switch have any deposits on it ? Are the heater control levers / cables operating fully ?
Hi James!! I will check the heater control cables to see if there is a problem there? It seems really strange that the problem only arose once the new radiator was fitted? There didn't seem to be any sludge in the system either? Bit of a mystery really? I think I will drain the system and remove the bypass valve and clean it up to see if that helps? Any other suggestions? Cheers Alpenweiss2
Only ... to make sure that the system is bled thoroughly, run the engine up to temperature with the cap off the expansion tank and the heater on max.
Well I have done that already! As I am going to drain it again to check the bypass valve, I think I will replace the coolant temperature sender as well (black one) and also get a new copper washer for the sensor in the radiator and PTFE tape the thread as well! If all that doesn't work, then I guess I will invest in a new VW thermostat and take it from there!! Cheers Alpenweiss2
oil and coolant temps are fine, half way or just under is where you want it to be. if heater is still cold at the se temps then its the valves that have gone or a blocked matrix most likely. read the coolant system faq! if one of the sensors was broken then id expect a totally different reading from the other one, but both sensors seem to be reading the same. if stat had stuck open the oil and water temps would be way lower, and if stuck shut they would be way higher, so dont change it.
Hey Rubjohnny! Well I'm relieved to hear that i won't have to change the thermostat..although the thought of fitting a new matrix fills me with dread!! The heater doesn't blow cold air, it is just about lukewarm..not really good enough?? It was fine a few weeks ago? Hmmmmmmm??? alpenweiss2
Did you sort the weeping sensor? Surely the sensor leaking that low on the cooling system is a potential cause for an airlock. Have you felt the heater pipes? Do they get hot? If they are hot upto the valves what is the temp like after the valves? If it were me I would bypass the valves as a temp measure to see if it improves.
fix the sensor, then bleed/check the system as per my coolant guide then see where you are. also before you do the matrix take out the centre console, dash under trays, all 4 heater vents and the surrounds they sit in. remove the 2 vent pipes and the plastic cover on the front of the airbox they connect to. now you can see inside the air box to check the condition of the flaps in there, if the foam has fallen off, theres your problem! give em a load of duct tape to cover the holes on the metal flaps and see how it is then.
