Very cold starts

Probably a defective temperature sensor not properly adjusting the fuel mixture for the conditions.

Because it's cold

HTH

or an air leak that reduces with heat or is adequately compensated for when warmed up. or maybe just a dodgy spark plug or lead, tracking coil etc. etc. the list is quite long without doing some diagnostics. A squirt of carb cleaner up the air intake will show (by better running) if it is too weak.

Or shagged plug leads not liking the damp.

Do they have plug leads? I thought the coil was on the plug with no lead, but I could be wrong, if so then add HT tracking to the list.

I have no idea...just general advice.

All of the failed temperature sensors I've come across have gone open circuit and therefore to max fuelling. Which just shows I've not come across ones with a positive coefficient or have shorted. ;-)

There's also a rare symptom of very cold weather with oil that's too thick. The increased oil pressure can pump the hydraulic lifters up and the valves don't shut fully. I've seen it happen on CVHs and the early Zetec engine was well known for it. The engine will run very rough, if it starts at all, until the oil has thinned out again. Might be worth checking you have the correct grade of oil in and not some cheap 20/50. It's more likely to be something else though.

I came across that once on a mark 5 escort, it span over like it had no compression, fired on one and eventually got going on the rest and was perfect when warmed up. I serviced it and the problem never recurred.

On Tue, 20 Jan 2009 09:19:24 GMT, I waved a wand and this message magically appears in front of Mrcheerful:

I'll check the oil level. I also think there might be a very small oil leak somewhere because I keep topping it up every thousand miles or so, and I certainly can't smell any burnt oil from the exhaust (can catalyst exhausts hide the smell?)

Checking the level isn't going to tell you anything. Either it has the right grade of oil in or it doesn't. I'd suggest something like a 5/30 synthetic in this weather if it isn't already using that. Most modern engines ought to be running on something thin like that anyway. Look in the handbook.

Vehicles with cats will not give out any oil fumes when hot (while the cat still works OK), but can when cool. A top up (litre or so) every thousand is within normal usage.

On Tue, 20 Jan 2009 13:02:56 GMT, I waved a wand and this message magically appears in front of Mrcheerful:

I've just checked the oil and water. Oil seems ok, just topped it up with 10W40 oil as that's what suitable for the car given its age and mileage (257,000 miles and still going).

Unfortunately the level of coolant was rather low, given that it had some more antifreeze added to it a couple of weeks ago so it was at maximum. It was below its minimum level, so I've topped it up to the minimum level with water, intending to add some antifreeze later so it doesn't get too dilute. I think there must be a water leak somewhere. The colour of the coolant hasn't changed (the coolant tank is transparent) so it's hopefully not a leak inside the engine.

An internal leak would give you rough running till it clears the water out. I would get a head gasket leak test performed immediately, don't leave it, as the fault will compound and may even get terminal. Coolant colour is not a guide as to head gasket failure.

>

On Tue, 20 Jan 2009 14:59:10 GMT, I waved a wand and this message magically appears in front of Mrcheerful:

How could an internal leak inside the engine be repaired? And how big a job would it be?

The internal leak would likely be head gasket failure, repair is possible but may be obscenely expensive on your vehicle. A likely figure is between

750 and a thousand to have a garage do it, more if the head/s are damaged or corroded or extra unforeseen bits are needed. You may have difficulty finding a garage that will do it at all.

First thing though is to get a head leak test done, using a coolant gas analyser, the simple colour change variety will do, also known as a 'block test'