I am Surprised. Every year I get phonecalls from Dozens of people advising me of their overheating problems, but refusing to diagnose it or going through basic maintenance. First thing check out at what Road and Engine speed your vehicle is overheating and then use a radiator/block cleaner on your cooling System after which you can flush it properly. Remember to also clean the radiator Air path. Then you fill it with clean water fit the Cap and let her warm up watching for leaks. Fix the leaks! Then you bleed the system of Air and go driving noticing if she heats up as before or not, then you can diagnose. Now if it seems if I wrote the above for a fool, fear not, there seem to be plenty Experts who don’t bother going through ALL the Basics. Oh yes, if she Overheats, wait for her to cool down and then check the radiator fluid- if its dirty, you have not cleaned the system properly, if its oily, consider your head gasket a goner, the same if she bubbles at idle. Actually a gone head gasket is good news because you can send your Head to someone like us and have it PORTED and repaired, please just find out first why it went.
Now for the Symptoms:
Seems to overheat regardless: Thermostat, Waterpump or Blocked System. Maybe a too small radiator?
Low Rpm is often a cause of Water circulating to slow through the radiator caused by the wrong Pulleys or a shot Pump.
Low Speed is normally caused by the Fan not getting enough cooling Air through the Radiator.
High speed, does not need a fan, could be that your Pump is circulating the Coolant to fast.
High Rpm, low speed could mean your radiator is flowing coolant to quickly or your flex fan is opened up and is not flowing Air, (A clutch or solid fan is a better deal on a 4*4).
The moment your motor is under Load, seems to be typical of an undersized or inefficient radiator.
An Aluminium Radiator is more efficient while a Brass one is easier to fix in the field. A shroud is essential, unless you want to use a Gruntous Fan! The “Antifreeze” is more a Corrosion protector and a system to increase the Boiling point of your radiator, as well as something to lubricate your Waterpump. Another way to increase the coolants Temperature is by pressurising it- that is the job of your cap. I personally prefer fitting the Radiator with the largest frontal Area to a vehicle, but with the laminations to be far apart and not too deep. The stock temperature gauge is normally inefficient and I personally prefer a decent aftermarket unit that is well calibrated. Below 74 C is to cold, while 100 C is hot and from about 120 C you start damaging the Motor.
A wrongly adjusted carb or dissy can also make the temperature soar. Also remember a Rebuilt motor often runs hot until it has run in. This is because of the tight clearances, my own Buick did so for 40 000 Km’s because it seldom runs high RPM which will speed up the break in process (and decrease life expectancy). If a radiator has many close lying capillaries it can often block itself, especially during Slow Road speeds. Increasing your coolant amount (large radiator tanks, swirl tanks etc.) will make a car take longer to overheat. Spotlights, spare tires and a lot of things can restrict cooling air to your radiator.
Inside your cooling system the following happens; The Combustion process generates Heat, which is absorbed by the Oil and water. A Thermostat then opens at a preset Temperature (82- 94 c) and the Waterpump then Circulates the Coolant through your Block, heads radiator and heater. If the Coolant drops below the thermostat temperature, it closes letting the motor not get to cold to do damage. If you drive without a thermostat, it is probably to late to help you- read my Engine rebuilding Article, which is to appear in the future! On an efficient cooling system the thermostat should never be completely open. Should your Coolant get to hot the pressure in the system increases and gets blown off through the Cap.
Now for your Oiling system. It is pretty difficult to get the coolant temperature within limits, if the oil reads 180 C! Apart from that Oil is part of your Engine cooling system, and on some Motorbikes it is the only cooling system. Quite a few American Vehicles get to overheat at high speeds simply because they have to little Oil. An oil cooler is step #1, but please ensure that the oil is only circulated through it from a preset temperature. Cold oil is thick and can harm motors bearings, while also putting excessive stress on the Oil pump system. That is why a Race motor normally is warmed up until the Oil Temperature gauge shows over 80 C and for the first few laps the driver revs the motor according to oil Pressure!
Ok by now you will have noticed that ignoring your cooling system gives you about as much chance as a head of cabbage at a rabbit convention. If your vehicle runs to cold, your clearances are too tight meaning excessive wear or even seizure. Too hot means that you will not notice temperature runaway and your rings can only take a certain amount of heat before becoming pap. A lot of people advise colder thermostats for more power, listen what GM says (that’s general Motors, not my friend with the loud voice). “ Competition and street engines should be run as hot as they can be run without encountering problems, as hotter-running engines improve fuel economy and horsepower” – “ heat pumped into the radiator is horsepower the engine is not feeding to the driving wheels” – “you should shoot for an operating temperature of 180 degrees “ that’s 82 C for the youngsters.
If you are now as confused as a Baby at a topless bar, you can always go to a knowledgeable radiator place. But beware there are a lot of sharks out there that seem to use a customers ignorance to further their exorbitant lifestyle. Case in Point; we modified a Mazda 2.6 to push out 30 % more power. Thereafter we advised the owner to have his Radiator cleaned, due to years of abuse of him filling it with water from the dam (I would not want to know where else that mud in his cooling system originated from). His Radiator shop convinced him to Install a Heavy Duty Radiator due to “ that’s what you need with a Modified Motor” (not even a Turbocharged 2.6 needs more than a stock radiator) Annycase thereafter he continued overheating his car at low speeds, such as when checking his farm. This was due to the Radiator fins being to tightly spaced, to let air through! A stock radiator cured all his problems. Of course said radiatorshoppe did not want to hear any of his problems once they received his money, hopefully they will shut down soon to protect us all.