George - changing the oil and filter on your car is the simplest and most important thing you can do to ensure your (expensive) car gives you a long life. I do mine twice a year regardless of mileage. It takes half an hour and costs £15- £20 depending on what oil you use. Lecture over! Now the good news.
Luke warm heating DOESN'T suggest head gasket to me (though the mayonnaise gunk could).
If you're planning on keeping this car then I would suggest it needs a good 'going over'. Drain the cooling system, flush out the radiator, renew the coolant and antifreeze, change the oil and filter and air filter and spark plugs. When you've done that (£50? - DIY) see how the car runs.
Richard
January 2009
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