BDR/X Flow Cooling System - Closed or Open?

[anthonym]

yes, so how much liquid given there are no markings?

[OldAndrewE]

Not an easy question to answer and probably needs some experiment.  I would say as much as possible without causing the bottle to overflow.  If you are sure the system is properly full with no airlocks then I would start at 1/3  to 1/2 full

[Roger King]

Sealed system every time. Both systems are pressurized, but the "open" version is meant to pull (alright, technically, atmospheric pressure is meant to push) expanded water back into the system. It just doesn't work properly, sucking in air instead, whereas a healthy sealed system never loses coolant, merely allowing it to expand into space within the system; i.e. in the header tank. You don't need a cap of any sort on the thermostat housing, provided you use a housing with no facility for a cap, and filling is carried out via the expansion tank. However, you MUST run a thermostat to prevent water rushing out of the top of the engine and straight up the hose to the header tank.

The most common fault with an "open" system is for a driver to check their levels, go out and do a morning session of a track day, and then forget to check the water level for the afternoon. What will have happened is that a significant amount of coolant will have been expelled into the catch tank, but not been drawn back as the engine cools, resulting in lovely great air pockets forming in the cylinder head at exactly the point where cooling is most critical. The afternoon session should then be just enough to cause major damage. The difference in head gasket failure numbers and overheated exhaust valves between the systems has to be seen to be believed.

[Ian Macquarie]

The cap needs to seal in 3 places. The low pressure fluid return that you highlight in your first picture #23, the high pressure relief against the lower part of the filler neck and the top sealing ring against the top of the filler neck. From the last photo, it looks as though part of the sealing ring at the top of the filler neck is missing / damaged. If the filler is damaged then you may be sucking air in there rather than sucking water from the overflow container. It could of course just be a trick of the light and the filler neck may be perfect!
Ian

[anthonym]

trick of the light, fuzzy pic but you can see - it's a brand new cap. 

I feel I will be forced to do the sealed system, just be nice to avoid even more work. -

this evening's test has resulted in less than full bottle and the engine is still hot, so will check again later, and temp went to about 95c  where previously it had sent steam through the bonnet.

anthony

 

[Ian Macquarie]

I expect you're right but it was the arrowed area on the filler neck that I was looking at.
Roger has far wider experience than me - I'd listen to him. At the moment the unsealed system seems to be working on my 1990 crossflow.

[anthonym]

o i c - I'll have a look when the cap comes off (currently still too hot).  

 

edit it will be very cool if you have spotted something

[jbcollier]

The stock system is a pressurized system.  It is designed to be completely full at all times.  As the coolant heats up, it expands and excess volume is released into the reservoir when the rad cap's pressure rating is exceeded.  The correct cap is double sealed so that when the coolant contracts, coolant flows back in from the reservoir.

Any leaks in the system will result in the coolant being pushed out but not drawn back in.  The coolant level in the engine will drop leading to overheating.

The same problem happens when people replace the sealed system cap with an ordinary cap.  Again, coolant is not drawn back in leading to coolant loss and overheating.

I would recommend making sure the system is worKing as designed before modifying it.  YMMV

[GordonW]

The thermostat housing with the top bleed fitting as mentioned by RK in the original post is available on ebay, search -

"Thermostat housing to suit Ford Fiesta Mk3 6814635 New"

Should you choose to go this route.

It's what I used to good effect.

[anthonym]

Yes I have a new one based on the Ford part number and it has the required pressure release valve. How to test that is s question. 
 

If air is getting in, it is doing so without losing fluid.

Air must be getting in.

My current suspect is the quality of the seal between the outer seal in the cap and the stat housing. The cap is new but the stat housing surface is 37 years old.

The inner seal looks a bit approximate, but that shouldn't stop the fluid retirn process Anthony