Thought I'd start a new thread since my last one went off on a tangent.

Rebuilt the head on a 1.6 16V petrol mk6.5 and the coolant needed topping off the last couple of days by about a pint or two. I can't remove the radiator bleed screw so have relied on squeezing hoses and topping up after short trips to and from work today. It looks like I need another half to a pint to get it to max now. I'm assuming it will settle very soon, am I correct? The heating has been on full for at least five minutes driving today and I topped that off at work with a pint.

There is no water vapour from the exhaust, no abnormal pressure in the expansion tank and the oil is clear (although I need to do another oil change after rebuilding the head). There are no obvious leaks but, will stick some cardboard under the engine bay this evening if I can find something suitable in recycling, to detect smaller leaks.

It might just be pockets of trapped air working their way around and to the expansion tank. In the absence of an obvious leak I wouldn't draw any other conclusions just yet.

Thanks @MJNewton it's only been three days driving, topped up another pint today, half a pint yesterday. Your response gives me some reassurance.

The idle was a little lumpy though nothing like before the gasket job or the broken plug, just something not quite right. I popped some Redex in and ran it to around 3K RPM for a couple of minutes and could hear some gurgling from the heater matrix, the coolant hand't gone down at all after that time. I hoping that's the last top-up, but I think I've put in over 5l in total, so there could be a small leak. I'll find a big bit of cardboard and leave it under the engine bay for a day or two this weekend to see if I can spot something.

The lumpy running has reduced too, so I'm feeling a lot better about it. Going to replace the fuel filter. The clips on the intake hose from the airbox to TB are missing so ordered a couple of jubilee clips to secure it properly. Fingers crossed!

Not worried about the lumpy running any more, it's improved massively since putting in some Redex.

Did a drive today and the coolant level went down by about half a pint. I'm thinking about changing the steering pump belt to a 2mm larger one tomorrow due to a squeak when steering. The original belt was 692mm, the replacement one that's on is a 690mm, so got another 692mm. So the car will be jacked up, I'll pressurise the system with a pump to about 20 psi and see if I can spot any leaks.

Edit: Just read this 

I'll let it drop and keep and eye on it. Could be the cap needs replaced though.

Edited May 10, 20251 yr by MAH310583

Just a quick note: checked the cap, outer seal was good condition, flipped it over anyway. When I compressed the spring it was initially very difficult to do and appeared stuck, now it's not and moves freely. Ordered some more silicone spray and will treat it. Doesn't explain the coolant loss though, it's probably there's a leak under pressure I haven't spotted yet and this might reduce or stop it if it wasn't releasing pressure at around 20 PSI.

Saw a mark on the drive this morning where the car had been overnight, looked like it might be pink coolant, so assumed the thermostat housing wasn't sealed properly. Four hours later and a new belt on the power steering, it's not the thermostat housing.

Ran it up to temp, could see and feel the heat, the coolant surface being agitated by the pressure coming in and still no leaks. I noticed the tube wasn't fully on, it is now. Still can't see anything, so probably just paranoid. I'll get another bottle of coolant, run it round for the week, topping up as necessary and cross my fingers.

These engines can be a pain to bleed the cooling system.

The easiest and most reliable method is vacuum filling. During this method the cooling system is vacuum tested for approximately 30 minutes. If the vacuum does not drop within the 30 minutes the cooling system is OK to be filled. The vacuum inside the system is used to draw the new coolant into the system without introducing any air pockets.


As an alternative to vacuum filling the following method can be used (this is basically a 2 person job):

1. Raise the front of the vehicle 15 to 20 cm.
2. Remove the cap of the coolant bottle.
3. Run the engine at approximately 2000 RPM until the thermostat opens.
4. Make sure the coolant remains at the correct level (add coolant if the level drops).
5. Switch the engine off.
6. Lower the front of the vehicle and make sure it is level.
7. Check the coolant level and correct if required.
8. Install the cap of the coolant bottle.


Remember that an air pocket that is trapped inside the engine block in worst case scenario cn result in partial overheating without any warning light or message. This is why vacuum filling became the prescribed method Years ago. 

Thanks @JW1982

I'll try to get it up on ramps soon and get squishing those hoses. Will take it down a notch or two onto a couple of stands and do the same. I did take the top hose off the radiator this evening because I can't get the bleed screw loose, a little air came out along with fresh coolant from the hose and radiator.

The level didn't change much on this morning's drive, but there was about 1/4 pint missing this evening. Ordered more coolant and a new tank and cap - when I was doing the belt and checking the thermostat yesterday I noticed a wide pink stain on the inside of the lower aux belt cover, directly below the tank. I've also noticed increasing dampness below the thermostat housing which is brand new with the new thermostat so, might need to add some liquid gasket to it.

What a PITA this is.

This explains a lot...

It's replaced, along with a new cap. Not Ford part, so I might end up paying more later. 🤞 I didn't notice it when doing the head gasket and moved it out of the way to get more access to the belts, the pigment in the new coolant highlighted it.

The alternator had started to fail, so I added some liquid gasket to the thermostat housing as well - belt & braces - another alternator fitted and almost all back together. Took a bit over two hours with quite a few breaks.

Leaving the sealant to dry over night, will refit belt, headlamp, wheel back on and coolant refill tomorrow.

Got one of these for the stretch belts...

It's solid though the belts need extra help to come off and go back on, not the best but makes the job a bit easier. This is the fourth time I've stripped down the intake, alternator and thermostat housing to solve various problems which were missed when I did the head gasket.

Finally realised you can loosen the injector rail bolts slightly and remove the whole intake at the same time. The second time I did it, I stripped the thread on the rail bolt on the battery side. Repaired with stripped screw hole repair strip shaped to the hole with the rough side out, hammered gently into the hole and used a handy saw to cut the excess off, worked a treat!

Fitted the new tank, refilled and managed to combine the RELD kit tank bung with a vacuum break bleeding kit to get enough vacuum to bleed most of the air out. This uncovered the fact I'd forgotten to tighten the jubilee clip on the lower radiator hose to the thermostat housing, thankfully I could get to it with a flexi drive adapter on my cordess driver. I then attempted the method of getting it up to temp and revving 2K-3K for 30 seconds to get any air out, which worked partially but made a real mess so let it cool for a while.

Went back for a second try, this time to check pressure was being held too, so revved 2K-3K for 30 seconds at a time and could hear the air from the heater matrix getting moved. Each time I checked the tank by releasing any pressure and topping up. Did this about three times, the third time there was no bubbling so let it get up to temp and then very slowly released the cap - plenty of pressure but noticed a tony leak from the lower hose to the radiator. I'm hoping this is just a matter of repositioning the spring clamp to it's original position on the old hose. All being well, job done but, I don't trust the new cap, so using the original Motocraft one.

Very crudely tested the pressure resistance of the new cap with the old by pushing on the valve, the new one seemed to required only slightly less pressure to release than the old one. Given the split on the old tank and even though it was possibly caused by the recent gasket failre, I've switched back to the new cap today. I'm just paranoid the new tank is going to split on the seem.