Header tank cap issues

Fox3 · 26th January 2018, 08:31

I'm losing coolant from, what appears to be the header tank cap. I've changed the cap for a new one and it’s still the same.

What purpose does the tiny hole on the left hand side of the neck of the tank do? Mine spews out coolant when topped up to the correct level, but from what I can see this is sealed between the two O-rings on the cap.

I've been chasing my tail with the coolant system for some time now, the previous owner repaired a leak with a 'few' tins of rad-weld that I'm pretty sure has caused a number of the issues I've had.

Any help would be much appreciated, I'm going through about a litre of coolant a week at the minute!

fandango151 · 26th January 2018, 08:47

Silly question but when you say correct level where do you mean ?The level is actually a max marker in the bottom of the tank not the neck so looks pretty empty. If it is filled to the brim it will overspill and pop passed the cap.

Sorry if it sounds patronising but the header tanks are not intuitive on these.

Fox3 · 26th January 2018, 08:57

Thanks for the reply, I can see the max 'step' in the bottom and try to avoid overfilling it.

It seems to spew out until the heater goes cold, then requires about half a litre to get back up to the min level

trikey · 26th January 2018, 09:06

Quote:

Originally Posted by Fox3

Thanks for the reply, I can see the max 'step' in the bottom and try to avoid overfilling it.

It seems to spew out until the heater goes cold, then requires about half a litre to get back up to the min level

Try changing the tank next, I have heard of one or two being the culprit.

T-Cut · 26th January 2018, 09:50

Quote:

Originally Posted by Fox3

What purpose does the tiny hole on the left hand side of the neck of the tank do?

Read this: https://www.the75andztclub.co.uk/for....php?p=2293452

Quote:

I'm going through about a litre of coolant a week at the minute!

Are you sure all that is being lost via the header tank cap? Diesels rarely get warm enough to have pressure cap ejection issues, but are prone to simple leaks. A common leak spot is the thermostat housing. Both the main housing o-ring/gasket and the coolant rail to housing o-ring are common failure points. Of course coolant might leak from any of the dozens of joints in the system. It may need careful examination to find them.

TC

Fox3 · 26th January 2018, 13:36

Thanks TC, very nice piece of work there!

I've fixed a leak near the FBH location and the top radiator elbow.

I cant see any evidence of coolant elsewhere, apart from the top of the expansion tank.

I did have an issue with it holding pressure for days, I've found another thread on here with similar symptoms to mine, it turned out to be a blocked oil cooler.

26th January 2018, 08:31	#1
Fox3 Avid contributor MG ZT CDTi and MG ZT 190 Join Date: Oct 2016 Location: North Yorkshire Posts: 188 Thanks: 53 Thanked 45 Times in 30 Posts	Header tank cap issues I'm losing coolant from, what appears to be the header tank cap. I've changed the cap for a new one and it’s still the same. What purpose does the tiny hole on the left hand side of the neck of the tank do? Mine spews out coolant when topped up to the correct level, but from what I can see this is sealed between the two O-rings on the cap. I've been chasing my tail with the coolant system for some time now, the previous owner repaired a leak with a 'few' tins of rad-weld that I'm pretty sure has caused a number of the issues I've had. Any help would be much appreciated, I'm going through about a litre of coolant a week at the minute! __________________ 2003 ZT+ CDTI

26th January 2018, 08:57	#3
Fox3 Avid contributor MG ZT CDTi and MG ZT 190 Join Date: Oct 2016 Location: North Yorkshire Posts: 188 Thanks: 53 Thanked 45 Times in 30 Posts	Thanks for the reply, I can see the max 'step' in the bottom and try to avoid overfilling it. It seems to spew out until the heater goes cold, then requires about half a litre to get back up to the min level __________________ 2003 ZT+ CDTI

26th January 2018, 13:36	#6
Fox3 Avid contributor MG ZT CDTi and MG ZT 190 Join Date: Oct 2016 Location: North Yorkshire Posts: 188 Thanks: 53 Thanked 45 Times in 30 Posts	Thanks TC, very nice piece of work there! I've fixed a leak near the FBH location and the top radiator elbow. I cant see any evidence of coolant elsewhere, apart from the top of the expansion tank. I did have an issue with it holding pressure for days, I've found another thread on here with similar symptoms to mine, it turned out to be a blocked oil cooler. __________________ 2003 ZT+ CDTI

26th January 2018, 08:47	#2
fandango151 Loves to post Rover 75 Join Date: Jul 2015 Location: Tamworth Posts: 291 Thanks: 2 Thanked 72 Times in 65 Posts	Silly question but when you say correct level where do you mean ?The level is actually a max marker in the bottom of the tank not the neck so looks pretty empty. If it is filled to the brim it will overspill and pop passed the cap. Sorry if it sounds patronising but the header tanks are not intuitive on these.