QuestionHow to proceed in logical steps to eliminate OVERHEATING.
AnswerThere are two ways to go at any problem: the fastest way to cure a problem is to attack the possible causes in the order of likelihood -the most likely cause first. The cheapest way to do it is to attack the causes in order of cost and trouble to diagnose, the cheapest and easiest first.
I am assuming in the following discussion that the engine runs well, and has normal power - if that is not the case, diagnose and fix the engine problems first - otherwise you may be chasing the wrong gremlin entirely.
I am also assuming that by "overheating" you mean that after a normal drive in normal weather, you have a pegged temperature gauge, sounds of boiling when you turn the engine off after a drive, and water coming out of the overflow tube after a drive (and you didn't overfill the radiator - only fill it to 2 inches below the cap!)
I'll just list the possible causes in order of ease in diagnosis.
1. Take the radiator cap off and using a flashlight, look in the top of the radiator to see if the top ends of the tubes are clear of debris. If not, have the radiator removed and "rodded out", then flow checked. If the tubes look clear of debris, go to step 2.
2. Go to a supermarket housewares department and buy a "Candy Thermometer". This looks like a giant glass/mercury fever thermometer, about 12 inches long (or you may take one from your kitchen, if your cook isn't watching). Now, fill the radiator until the water level is above the tube tops and stick the thermometer in the top of the radiator. Then start the engine, and allow it to idle until it comes up to normal operating temperature. Keep feeling the top radiator hose as the engine warms up, and look into the top of the radiator and watch to see when the coolant begins to flow sideways across the tube tops. This should happen somewhere near the thermostat setting, and the upper radiator hose should stay cold until that happens, then suddenly warm up rapidly to pretty hot, assuming you have a thermostat installed. If the coolant does not circulate rapidly when the thermostat opens, you may have a bad thermostat, or your water pump may be not pumping well, due to a failed water pump impeller, or a slipping belt. Investigate.
If the coolant starts circulating at about the thermostat setting (180, for instance), look at your temp gauge on the dashboard- to see if the two instruments agree - 180 should be somewhere around normal on the gauge. If it does, you've eliminated a bad gauge from your causes, and also eliminated a bad thermostat.
If the coolant starts circulating immediately after you start the engine, your thermostat is missing or failed. This isn't causing your problem, but it is an indication that some previous person has removed it - leading to a strong suspicion that this car has had this problem for some time.
If everything seems OK so far, and assuming the engine runs well and has normal power, we have narrowed down the overheating to two remaining likely possibilities.
3. Air flow: Next, inspect the front surface of the radiator for accumulated crud, leaves, dirt, greasy grit, excessive paint etc. Anything that restricts air flow will add to the problem. Also, make sure the fan is installed correctly and has the right blades and is the right distance from the radiator core. Make sure all air deflectors, flaps and sealing gaskets around the radiator are in place so as to force air to go through the radiator, not around it. Pay particular attention to the underside of the hood- if there are supposed to be rubber flaps there to seal against the top of the radiator to control air flow, make sure they are present and in decent shape.
#4. If all of the above looks OK, you are down to reason #4, which is probably the most likely cause, but the hardest to fix: accumulated mud in the block water jackets. Open the block water drain (or remove the brass plug from the drain opening, whichever is on your car. What happens? Nothing? OK, you've got crud in the water jackets. Poke gently with a tiny screwdriver into the drain hole. Dirty, rusty water will probably start squirting out. Stick a length of baling wire or the like into the hole and wiggle it around, then pull it out and look at it. Mud on it- diagnosis confirmed! Unless this clean out has been done within the last few years, and unless the car has been operated by the book (30% ethylene glycol or more, changed every 24 months) since it was cleaned out, the only cure is to remove the core plugs (AKA "freeze out plugs") and manually, using any tool you can find that works, and a high pressure garden hose nozzle, flush out all the crud you can get. The water jackets to the rear of the block are always the worst. If there is a drain and core plugs on the other side of the block, do those too. One can expect to get pounds of mud out of a neglected block. If the block is this bad, the head also has accumulated mud in it. If cleaning out the block only improves the problem part way, the head should be hot tanked to clean out the water passages. The water pump should come off the engine and the water passages behind it should be cleaned out too.
When you have the block and head free of accumulated loose crud, install a coolant filter in the upper radiator hose before you start the engine again - otherwise any remaining loose debris will wind up blocking the upper radiator tubes and you'll be back to step 1! I recommend the GANO coolant filter - because it is clear and you can see the crud accumulate before it blocks the water flow.
Dick
