philwalter 30 Report post Posted March 6, 2011 My M3 seems to be leaking a decent amount of coolant ( out of the overflow pipe by the looks) and when in stop start traffic the temp rises very quickly and up to a temp to be of concern. Would a leaky radiator cap be the problem ? With the cap on I can blow up through the overflow hose and hear the air leaking out of the cap. This shouldn't happen right ? Thanks :-) Quote Share this post Link to post Share on other sites
Mark 178 Report post Posted March 7, 2011 I'd say the viscous fan is shot. Quote Share this post Link to post Share on other sites
philwalter 30 Report post Posted March 7, 2011 Radiator fan is coming on if thats what you mean ? Did a test, left idiling in the driveway. Water temp gauge came up to 3/4 mark, fan came on and went back down to around half way mark which seems normal. So maybe its fine - and just replace radiator cap as that is leaking pressure for sure. Quote Share this post Link to post Share on other sites
Dave@nz 11 Report post Posted March 7, 2011 (edited) Hi Phil, Temp should run at about 1/3 mark when th engine is at full temp, If it has a viscous fan on the water pump this may not be working properly or another problem could be the thermostat not opening fully. I have a very good used thermostat which works correctly for sale if you requir one. Check that the water return line from the L/H side of the cylinder head to the catch tank is not blocked. Dave. Edited March 7, 2011 by 87M3@NZ Quote Share this post Link to post Share on other sites
