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Sigma 1.6 engines - loosing (a little) coolant over time?

Dave Eastwood (Gadgetman) - Club Secretary

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Dave Eastwood (Gadgetman) - Club Secretary

In Ford Focus world, this is a known issue, but I've not really heard it brought up on here, before, so....


For those Westfield owners with the Sigma 1.6 litre engine, sometimes known as the Zetec SE, it's worthwhile periodically inspecting the core plugs on top of the cylinder head - they're know to rot, and on occasional use cars like ours, it can take less time than you might imagine! They are in a slightly fiddly spot to get to, but it's only a five/ten minute job to give a basic look see.


Because they can fail quite gradually, if you only mainly do short cross country blats, you may not even notice the coolant loss, as apart from the lowering level in the header tank, there aren't any outwardly visible signs, till you've lost quite a lot!


Note, running temperatures are barely affected, because of where the leak(s) are.


To check, you need to take off the Spark plug cover, if fitted, on top of the cylinder head, then pull out the centre two spark plug leads from the head, so that you can look down, through the cam cover into the valley below. If you can see water in there, you may have leaking core plugs and will need to dig deeper, and remove the cam cover. If it's all dry. You're good to go!


Sadly, I knew I had a bad leak, when the engine was under load and revs on long trips with lots of dual carriageway and or fast a road overtaking, so for me, once I'd spotted the coolant, it was on to the next step...

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Dave Eastwood (Gadgetman) - Club Secretary

With the cam cover off, I had about 1/2 -3/4 Litre of coolant sat in the plug valleys - I used a wet/dry vac with an adapted nozzle to get the coolant out, and mopped up what was left with paper towels.






(Note, I did start removing spark plugs for easier access, but in my case it proved unnecessary!) You can clearly see the two 25mm core plugs in the picture above, not perfect, but not horrendous. One in each plug valley, facing upwards, between the plugs. (Engine has circa 12000 on it now and was supplied new with the kit).


A visual check from above didn't really prove much, so I hooked up a pressure tester, and let the system sit, with 1.2 bar pressure applied. (The workshop manual is 1.2 bar held for two minutes), which was sort of inconclusive. So I gave it another five minutes, and coolant could be very gradually seen rising from the core plugs. Left overnight, untill the pressure bled away by itself, this was the scene the next day!






So, all was drained out and dried off again. And a set of replacement core plugs, (and spark plugs) ordered from the local Ford dealer. (Who were also cheaper than quite a few of the online suppliers for the core plugs.)




After picking them up, it was time to swap them over - a task I was dreading, having taken out core plugs before. These came out rather worryingly easily! Only two taps with a hammer and punch in one case !! First step was to drain the remaining coolant out of the system, I also used the vac again, to get rid of some of the trapped coolant beneath the removed core plugs.




The bores they fit in weren't too bad, but needed a tidy up to make sure the faces were completely smooth and flat - a quick going over with a small wire brush in the drill soon did it, without getting any nasty contaminants into the engine.


Once on the bench, the old plugs were shocking - though do note, I'm positive that the hammering out and extraction process has made them slightly worse than when they were on the engine, opening up, what were pin hole leaks.


- Balanced on top of an inspection lamp, you can certainly see the light!




And the backs of them tell their own tale of woe...




The new plugs had a smear of Hondabond applied around the edges, and were carefully tapped home, using a socket, as a drift.




I let the engine have 24 hours, for the sealant to cure, before re-filling the cooling system, and re-running the pressure test - this time, fifteen minutes, no loss of pressure, and no tell tale moisture in the head valleys.


So, I swapped the plugs over - it must be said, at no time did I have any of the common symptoms, like missfires, that you get when the plug valleys are full of water - in fact you can see from the tide mark on the old plugs, that no coolant made it up inside the plug boots.




However the upper threads and hex sections of the plugs were nasty, and it was a false economy not to replace them. 


Once done, the cam cover went back on, and after a good clean up, and a spot of contact lube on the electrical connections, the plug leads went back on.




Still needs a bit more cleaning up, but pleasingly, it all started first time, and idled fine, with no weeps etc.


So, check those core-plugs!

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Thanks Dave. Top work, I'll keep an eye on my engine.



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