Cooling - Page 3

jimh · 23-10-21, 08:08 PM

A big temperature gradient from top to bottom of the rad like that seems to suggest slow flow though the rad (the water has plenty of time in the rad to cool before it is pumped back into the block).
If you've had nice, clean coolant for ages it seems less likely to be blocked and more like a feeble or not working water pump, or the thermostat is not opening fully.
Some water pumps have a plastic impeller that can detach from the shaft, some have a metal impeller that can detach from the shaft.

The thermostat is much easier to check / change than the water pump.

darreno'd' · 24-10-21, 06:04 PM

Thanks jim, both thermostat and water pump are new this year, I suspect limescale is playing some part as the last few years have seen very little use. Today though it decided to lob a load of water out the expansion tank after a run, all the time with the gauge in the middle, temp on the head outlet was 90 degrees, thermostat housing was 80 degrees and the rad seemed to be in the 70’s

jimh · 27-10-21, 09:43 PM

Did it spew the water on its own with the cap on, or as you took the cap off?
After shutdown, the water in the engine will go over 100 degrees and only the pressure in the system is stopping it boiling. Removing the cap will drop the pressure and allow the water in the engine to boil.

To flush the system, you're obviously going to have to drain the coolant.
I think if you remove the thermostat, you should be able to reach into the hole and check the water pump impeller from the back to check it hasn't come free on the shaft. Drop the thermostat in hot water on the stove.

Of course, it could well be that the rad is all blocked up with scale, it's just the thermostat & water pump are easier to check and get a definitive answer on - might as well verify when the coolant is drained.
How is the condition of the outside of the rad? Fins in place / reasonably straight / not filled with dirt etc?

darreno'd' · 28-10-21, 08:21 AM

Yes cap on Jim, water pump is new as is the thermostat, the rad is original as far as I can tell, but in externally good condition and not blocked or folded over on the fins. I think a good flush is in order first, to try and remove limescale. I had been considering going to waterless coolant, but no point if I have an underlying problem.

Isimmo · 28-10-21, 10:10 AM

If it’s the original radiator Darren, with the system drained you might as well send it off for a re-core during the winter downtime. Ours was re-cored by Guildford Radiators about 10-years ago. Came back like new and not had any issues. Think they might have been bought out since though.

BackintheFold · 31-10-21, 09:45 AM

Is the expansion tank cap new? If they leak they allow the pressure to drop and the coolant boils over.

darreno'd' · 31-10-21, 03:17 PM

Yep new cap too, I’d already considered that, no cracks in the tank either, I’m going to go down the radiator refurb or replacement route now, and also try for a good engine flush beforehand.

24-10-21, 06:04 PM	#22
darreno'd' Mr Sixty Thousand!! Classic Audi Club Member Join Date: Jul 2007 Location: berkshire Posts: 1,729	Thanks jim, both thermostat and water pump are new this year, I suspect limescale is playing some part as the last few years have seen very little use. Today though it decided to lob a load of water out the expansion tank after a run, all the time with the gauge in the middle, temp on the head outlet was 90 degrees, thermostat housing was 80 degrees and the rad seemed to be in the 70’s __________________ http://www.oesems.co.uk/

28-10-21, 08:21 AM	#24
darreno'd' Mr Sixty Thousand!! Classic Audi Club Member Join Date: Jul 2007 Location: berkshire Posts: 1,729	Yes cap on Jim, water pump is new as is the thermostat, the rad is original as far as I can tell, but in externally good condition and not blocked or folded over on the fins. I think a good flush is in order first, to try and remove limescale. I had been considering going to waterless coolant, but no point if I have an underlying problem. __________________ http://www.oesems.co.uk/

28-10-21, 10:10 AM	#25
Isimmo Super Moderator Classic Audi Club Member Join Date: Jul 2007 Location: Sissix-by-the-sea Posts: 15,218	If it’s the original radiator Darren, with the system drained you might as well send it off for a re-core during the winter downtime. Ours was re-cored by Guildford Radiators about 10-years ago. Came back like new and not had any issues. Think they might have been bought out since though. __________________ 1985 WR quattro, 1985 20vT RallyRep, 1993 MTM ABY S2 Avant. 2010 S3 Sportback.

31-10-21, 09:45 AM	#26
BackintheFold Senior Member Classic Audi Club Member Join Date: Feb 2019 Location: Near an MB ur Quattro Posts: 1,171	Is the expansion tank cap new? If they leak they allow the pressure to drop and the coolant boils over. __________________ 2006 A3 (daily drive) 1987 MB ur

31-10-21, 03:17 PM	#27
darreno'd' Mr Sixty Thousand!! Classic Audi Club Member Join Date: Jul 2007 Location: berkshire Posts: 1,729	Yep new cap too, I’d already considered that, no cracks in the tank either, I’m going to go down the radiator refurb or replacement route now, and also try for a good engine flush beforehand. __________________ http://www.oesems.co.uk/

23-10-21, 08:08 PM	#21
jimh Grown up member Classic Audi Club Member Join Date: Dec 2008 Posts: 122	A big temperature gradient from top to bottom of the rad like that seems to suggest slow flow though the rad (the water has plenty of time in the rad to cool before it is pumped back into the block). If you've had nice, clean coolant for ages it seems less likely to be blocked and more like a feeble or not working water pump, or the thermostat is not opening fully. Some water pumps have a plastic impeller that can detach from the shaft, some have a metal impeller that can detach from the shaft. The thermostat is much easier to check / change than the water pump.

27-10-21, 09:43 PM	#23
jimh Grown up member Classic Audi Club Member Join Date: Dec 2008 Posts: 122	Did it spew the water on its own with the cap on, or as you took the cap off? After shutdown, the water in the engine will go over 100 degrees and only the pressure in the system is stopping it boiling. Removing the cap will drop the pressure and allow the water in the engine to boil. To flush the system, you're obviously going to have to drain the coolant. I think if you remove the thermostat, you should be able to reach into the hole and check the water pump impeller from the back to check it hasn't come free on the shaft. Drop the thermostat in hot water on the stove. Of course, it could well be that the rad is all blocked up with scale, it's just the thermostat & water pump are easier to check and get a definitive answer on - might as well verify when the coolant is drained. How is the condition of the outside of the rad? Fins in place / reasonably straight / not filled with dirt etc?