Portent 0 Posted March 20, 2012 Just wondering if mine is behaving as expected or whether it's worth swapping it out... When driving the water temp usually stays at about 70 deg (oil temp around 90 deg). However if I stop for a period of time with the engine idling then the water temp rises to almost match the oil temp. Is this the expected behaviour or should I swap the thermostat? Quote Share this post Link to post Share on other sites
CazzaVR 0 Posted March 20, 2012 Change it. Should be around 90 c once up to temp. Quote Share this post Link to post Share on other sites
fendervg 32 Posted March 20, 2012 Doesn't sound normal - it may be that your fans are not kicking in when they should - if you are sitting in traffic the temp will rise until the fans start - there is a switch on the bottom of the rad that controls this. Also check that your top radiator hose becomes hot once the engine is good and warm. Quote Share this post Link to post Share on other sites
Portent 0 Posted March 21, 2012 I think the fans are kicking in ok as it never goes above 90 deg on the water. But I will check it at the weekend and the hoses as suggested. I was going to do a coolant change soon anyway so I will factor in a thermostat change at the same time. Thanks guys. Quote Share this post Link to post Share on other sites
Stonejag 10 Posted March 21, 2012 (edited) What water temp should the rad fans kick in at? My temperature gauge has always read a little on the low side but since replacing all my hoses yesterday (thanks again, Stu!) the needle rests at approx 85º when cruising at 50mph and rises to approx 110º when sitting in traffic. However I don't think my fans are kicking in at all :( Shorting the two pins inside the connector for the yellow temperature sender does make both fans come on at high speed - does this imply my fan controller is working OK? Is there a more thorough way to test it? I had the radiator thermoswitch replaced with a new one 2-3 months ago but I suppose it could be dead, can one do the same pin-shorting trick to test them? I really want to make sure they are working OK since I am now using an oil-to-air gearbox cooler - I don't want it to roast itself sitting in traffic if the fans aren't coming on when the coolant temp rises. Stone Edited March 21, 2012 by Stonejag Quote Share this post Link to post Share on other sites
seanl82 23 Posted March 22, 2012 That's not good. It shouldn't really rise above 90. Are you sure you bled it properly? With 2 stag fans, I can't remember exactly, but the first one should kick in around 94, and second around 98. Run it up to warm at idle with the bonnet open, and watch for them to come on individually. If there only coming on together at high temp, it suggests the first stage has been bypassed due to a fault somewhere in the past, or it's just another dodgy sensor. I'm sure someone else will confirm though, mines just single fan so I'm guessing a bit here! Quote Share this post Link to post Share on other sites
Stonejag 10 Posted March 22, 2012 Are you sure you bled it properly? No :) What's the proper method? I've had it up nice and hot (and heaters on full) and then slowly undone the expansion tank cap - lots of air bubbled out and the coolant level dropped, then topped it up. Done that a few times. I'll have to have a play at the weekend, think there might be something on how to test them in the Bentley too... I've only ever seen the fans come on together, so could be a duff thermoswitch I guess. Quote Share this post Link to post Share on other sites
seanl82 23 Posted March 22, 2012 Run it up from cold with the expansion tank cap off. With the stat at 90, rev it up to about 2.5k rpm for 30 second periods. Do it a few times until the coolant starts bubbling up, then switch off and rinse any overflowed off with fresh water. Top up to max, job done. If you've not already done it, swap your stat out with a new o-ring and get a new housing as well to be safe. Its only a few quid, that with some fresh coolant should see it working much more efficiently anyway. :thumbleft: Quote Share this post Link to post Share on other sites
Stonejag 10 Posted March 22, 2012 I only did the hoses on Tuesday (and Wednesday morning...:oops:) so the coolant's pretty fresh anyway ;) Will give it another go at the weekend. Quote Share this post Link to post Share on other sites
seanl82 23 Posted March 23, 2012 Oh right, i wasnt sure if youbhad changed the stat already is all. Quote Share this post Link to post Share on other sites
Stonejag 10 Posted March 25, 2012 Bled it out properly yesterday and the level did drop a fair bit so hopefully I have got the last of the air bubbles out. Also noticed the aux pump running for the first time - it helps there's a clear section in the return to the expansion tank on my top hose so you can see it glug past! Neither of the fans came on while I was bleeding it, but if it's got really hot they do come on together for short bursts (ten secs or so at a time) once the engine's stopped. It's an auto so has the same extra temp sender as found on the cars with aircon - that's probably responsible. While bleeding it the temperature gauge never rose above 90 even when it boiled over so the reading is obviously wrong - reading the temperature from the ECU with VAGCOM (blue sender) it was 20º-30º higher than indicated on the dash gauge. As I said above, shorting the two pins on my yellow sender's connector makes the fans come on on stage 3, which would imply the correct bit of the harness is plugged into the correct switch and that the fuses are OK. Is there a more in-depth way to check the fan controller other than buying a new one and swapping them over? New parts in the last three or so months: water pump, thermostat, stat housing, crack pipe (second-hand) radiator fan thermoswitch, yellow sender (second-hand). I'll get a replacement yellow sender in new from VW and see if that helps the gauge read more accurately, but the fans not spinning still bothers me. It's fine at speed, but has been getting extremely toasty when I drive slowly (last time I was stuck behind a bus the oil temp reached 122ºC!) so it really needs sorting. Stone Quote Share this post Link to post Share on other sites
