Tips When in doubt - Change the thermostat, they are cheap and responsible for 40% of cooling problems. 40% is due to corrosion and buildup and the rest is mechanical failure, gaskets etc. Always keep the radiator water green (glycol) - prevents rust (read MUD), icing and shows your system is clean.It also raises the boiling point of the water, ie it will not boil at 100 deg/C. Remove all hoses, thermostat etc and blow out all hoses, radiator, head, heater at least once a year from all directions. On cars fitted with factory oil coolers, remove & clean it out as well (a pain), you cannot blow it clean in the system and it is a collecting point for mud. NEVER put water into a steaming radiator! - It will crack/warp your head and/or radiator.Let it cool down first! Never open a hot radiator! - leave it for 15min or ground the fan for a few minutes first. You will burn yourself and those around you. If it has boiled, it could vomit hot water at any time! Put a small amount of grease on all fittings before re-fitting the hoses - prevents rusting and will make removing hoses easier (No it won't leak). NEVER throw glycol (antifreeze) on the ground (kills the grass) or leave it lying around, animals (esp kids, dogs, cats, birds) will try to drink it (smells nice) and it's lethal! Do not mix diffent types of antifreeze, always empty into a pan and flush the system first. Always check new thermostats in boiling water first! Fill the system slowly, squeeze the hoses to check no air is in the system. Before upgrading your motor, seriously consider fitting a thicker, aftermarket radiator as well! Periodically check your fans are working. In sub zero temperatures and your car is not heating up properly - tape a piece of board or thick plastic over part of your radiator, experiment with different sizes. Mysterious loss of water and eventual overheating. Let car idle for 10 min and then check for water under the car, around the radiator (the top tank is suspectable to small cracks which leak under pressure) and the bottom of the cambelt cover and inside the car around the passenger footwell. Check exhaust for white smoke, white smoke = head gasket leak.Exhaust will be wet and sweet smelling. Check spark plugs - Any "clean" plugs will show where gasket is leaking. Check engine oil - white/milky oil indicates water in the oil. Check fan operation Check around engine block, welsh plugs will usually rust through and start seeping from the centre of the plug. They are bastards to find as the water will boil away on the hot block. Look for stains under the plugs. Same goes for small leaks around the water pump Gauge moves up and then comes down Thermostat is sticking and not opening fast enough, in that time the pressure has risen and dumped water into the overflow bottle. If the fan is faulty it could blow a hose or head gasket. Dumping water into overflow bottle Radiator cap faulty, replace Thermostat faulty, replace Fans not working - sender, fuse, relay, motor faulty Radiator blocked - clean entire system. Head gasket leaking gas into water - bubbles in radiator, steam. Perform pressure test. Burst Hose Thermostat stuck closed - remove it and immerse it in boiling water, if it does not open - chuck it. Major water leak - fill system and check for leaks Perform steps under tips to remove any potential obstructions. Check fan operation. Radiator cold in places Radiator tubes blocked It's overheating and I'm miles from home If there's a leak - fix the leak! - any water you put in will be pumped out in seconds. Refer to tips section before burning yourself. Make sure you have plenty of water and spare water in the trunk, keep the revs down (shortshift), coasting on flats, switch the motor off on downhills and WATCH THAT GAUGE! Frequent stops to check the water and grounding the fan sensor will help. Switch the heater to high heat and open the windows, it will help cool the motor. Spraying the radiator with cold water will also help DO NOT spray a hot engine block with cold water - you risk cracking it! If you can - remove the thermostat till you get home/garage. Fan/s not working Sender unit on thermostat housing faulty? Remove wire from sender and touch it to the motor, fan should switch on.If not it could be a fuse, sender, relay or fan motor. NOTE - fans will not work when radiator is empty, sender can only work when immersed in water not steam. Heater not working Heater valve on firewall jammed Heater radiator blocked - remove two hoses and blow out repeatedly with water. Heater radiator control flaps stuck, can be a cable or electric motor fault. Car takes ages to warm up Either your thermostat is jammed open, or Your motor is so worn, there's hardly any friction and it's running rich. Car takes ages to warm up and gauge drops lower than normal at speed Your thermostat is jammed open, not good. Refer to Thermostat section. Thermostat Always check new thermostats in boiling water first Never run without a thermostat or modify the thermostat, the engine temp will not be constant and take longer to warm up. Causes accelerated engine wear & gasket problems. Yeah I know race cars don't have them - don't do it a) they modify (restrict) the housing b) they are flat out all the time c) the motor is pre-warmed d) most use electric water pumps Water Pump The water pump bearing and seal will eventually go. When it does it will scream on startup and start to leak water or start/stop screaming loudly while driving - CHANGE IT IMMEDIATELY!- The water pump on these motors runs off the cambelt, if it seizes - it could destroy your motor There is an O-ring on the rear of the pump and a gasket on the front, if either leaks it is advisable to change the pump as well.