Drucey 10 Posted December 17, 2014 Right, took the car out today and let it get upto full temp. Again all the heater setting only blow out Luke warm air. (More like cold to be honest)would people say on here it's a thermostat problem still? Or would that be the best place to start? Thanks everybody. Quote Share this post Link to post Share on other sites
seanl82 23 Posted December 17, 2014 Turn the car on from cold. Let it idle on the drive. When the top radiator hose starts getting warm, check if the bottom one is as well. The bottom hose should stay relatively cool until the water temp gets to 90 degrees as seen on the gauge. If it gets hot well before, your thermostat needs replacing. Quote Share this post Link to post Share on other sites
Drucey 10 Posted December 17, 2014 Ok, thank you. Would this cause the air not blowing hot even after driving and at full temp? Thanks m8. Quote Share this post Link to post Share on other sites
seanl82 23 Posted December 17, 2014 Whilst driving yes. As I mentioned in a previous post, if the thermostat is stuck open (the failed state), the water is constantly being cooled by the radiator. When you stop in traffic for a while or sit at a standstill, there is no cold air flow over the radiator, so the water temp will increase and your heater should get warmer. Quote Share this post Link to post Share on other sites
Drucey 10 Posted December 17, 2014 This is the problem, it isn't just blowing cold air. Is upto full temp, does not overheat, but just blows mild warm air. Is it worth changing it (now I have a thermostat) and put a hose pipe through the system to give it a good flush out. Then put new coolant in? Quote Share this post Link to post Share on other sites
seanl82 23 Posted December 17, 2014 You mentioned in a previous post that it got warmer when sat in traffic. Right, read the previous post where I said about testing if the thermostat has failed. Once that has been done, we can advise further. It just seems we're going round in circles at the moment.......... Quote Share this post Link to post Share on other sites
Drucey 10 Posted December 17, 2014 Ok, I'll try tomorrow, it just today when I got home the car was at fully operating temp. The coolant temp reading like it does when sat in traffic and the air was only blowing cool when on hot. Appreciate your time in helping :) Quote Share this post Link to post Share on other sites
Drucey 10 Posted December 17, 2014 Right, been out and started the car from cold on the drive, as you said the top hose got hot and started to firm up & The bottom stayed cold. what is the next thing to do? the heater valves? (these are not the ones the car had from new) bought new ones a while back about 9 years ago. should i flush the matrix through with a hose pipe in both directions? would it help? or would you think its something to do with the the heater box? like said before the foam has been coming through the vents. Quote Share this post Link to post Share on other sites
seanl82 23 Posted December 17, 2014 Ok it sounds like the thermostat is doing its job. Start by bypassing the bypass valves with a bit of copper pipe straight to the matrix. Its quick, cheap, and easy to do so worth working through the possibilities in stages. At that point you could also try flushing the matrix through in both directions but tbh, if its well past its best then flushing won't make a great deal of difference. Once the above is done, replace the heater matrix. If there is no history of it being replaced relatively recently, then its worth doing. To change it, you have to remove the heater box anyway. At this point, you can replace the foam on the directional flap. The directional flap is the one you will be seeing the foam from. A separate small solid plastic flap provides the switching between hot and cold so that will not be the cause of what you're experiencing. Quote Share this post Link to post Share on other sites
Drucey 10 Posted December 17, 2014 ok, thank you. how/what do you do and need to bypass the valves. will this cause the matrix to fail if it does work? Quote Share this post Link to post Share on other sites
seanl82 23 Posted December 17, 2014 (edited) They were added years back as the matrix could sometimes fail and spill hot coolant into the cabin. The valves are pressure relief valves so should the water pressure become too high, it was diverted from the inlet pipe to the outlet pipe. (not flowing through the matrix). Newer matrixes are much more reliable and better put together, so the valves were not needed. To test, just remove both valves and the pipe that connects the two, and run some copper pipe directly to the matrix in their place. This obviously ensures the water passes through the matrix. Found a pic of my old valver when I did it. Remove these. Edited December 17, 2014 by seanl82 Quote Share this post Link to post Share on other sites
Drucey 10 Posted December 17, 2014 Thanks so much for your help. If this fixes the problem will it no ok to run without popping the heater matrix? Mine is a 1989 car (g reg) it is very well looked after tho. Hoping I can do this without the hassle of changing the matrix. Can you remember the size pipe you used? B&b will sell the pipes I'm guessing? Awesome help m8!! Thank you. Quote Share this post Link to post Share on other sites
seanl82 23 Posted December 17, 2014 I can't remember the diameter of the copper pipe sorry. If you measure the inner diameter of the hose that should give you an idea. It'll be OK running it short term I expect, but I'd change it out before too long. If the matrix fails, it'll spill hot coolant all over your feet and will steam up your windscreen pretty sharpish! If you have confidence in your matrix go for it. In the short term it's worth a try even if it just pinpoints your problem. Quote Share this post Link to post Share on other sites
Joe3954 10 Posted December 21, 2014 Looks either 15 or 22mm copper Quote Share this post Link to post Share on other sites
swiftkid 1 Posted January 11, 2015 Just found this thread, hopefully you've sorted it out now but useful for people searching for similar problem http://www.clubgti.com/showthread.php?261279-Heater-blowing-cold-not-hot-matrix-cleanse-and-air-flaps-foam-refurb-guide Quote Share this post Link to post Share on other sites
Drucey 10 Posted January 11, 2015 Flushed all the system today and bled it correctly, not had the time to get it upto the max temp today, will test this week. Put the hose pipe through the matrix, all seemed to gush out ok.. Did the thermostat test and the top rad hose gets hot and the bottom stays cold, could it be possible that it is "stuck shut" rather than open?? Would that cause the problem? Will see if both pipes get hot when at fully operating temp this week tho. (Just Preparing for the disappointment!!) :( Quote Share this post Link to post Share on other sites
seanl82 23 Posted January 11, 2015 Bottom hose should stay cold until at full operating temp (90 degrees). If it was stuck closed, you'd have overheating problems. Just leave it running for 10 mins on the drive and it should be up to temp. Quote Share this post Link to post Share on other sites
Drucey 10 Posted January 11, 2015 I'll try it this week and get it red hot, it never over heats and runs fine. Everything work as it should temp goes up when in traffic and down when moving. Just no hot air when selecting face blowers and only mild warm air when selected to window screen position.. The matrix seem to flush out ok, did it through both pipes and gave the system a good flush. Coolant was only 12 months old and still looked like new when was flushed out.... Let's hope it was just an air lock or something? I'm not holding my breath tho :-/ haha Quote Share this post Link to post Share on other sites
