Four Malpractices That Can Cause Overheat


Every morning you see your neighbor’s uncle cleaning the family car in meticulous detail, this includes popping the bonnet doing an untrained detail job on the engine cover, removing the pressurized radiator cap, cleaning off the coolant that smudged the rubber seal and all that shit that makes him like an auto guru and you wonder in amazement “oh boy, that car must be in tip-top shape!”. And one day you spotted the car smoking at the curb. What happened?

The Fountain of Life!

First, let’s intimidate your uncle with the workings of a modern car cooling system.

Show this to your uncle

If you’re asked by your uncle what the hell is that diagram, tell him to get his hands off your car specially at the engine bay.

  1. Removing Pressure Cap – The pressure cap has a rubber seal which holds the water pressure inside the engine’s water jacket, it is important that pressure is kept at manufacturer’s specification. Regularly removing the pressure cap for no reason will wear out the rubber seal and will cause pressure to leak resulting in weak flow of water around the radiator and engine. Tell your uncle not to do this again.
  2. Overfilling The Reservoir – While the car is operating at a normal temperature, the engine is still producing excess pressure, this excess pressure is dumped to the reservoir. If the reservoir is filled to the cap, the excess pressure will find the weakest part of the cooling system to release its outrage, and the last place you want it to happen is in your radiator hose. Tell your uncle to just fill the reservoir at the maximum level indicated properly. 


  3. Bypassing The Thermostat – That “sanga ng bayabas” you heard from your uncle, it has no purpose anywhere in your engine. Do Not Bypass the Thermostat! It’s there for a reason, it provides a supply of cooler fluid (water or coolant) from the radiator when fluid inside the water jacket of the engine is reaching boiling point. Do the math, if the radiator water temperature and the engine water temperature are equal, there’s no way to go but up to the “fountain of life”.

    That uncle, is a thermostat

  4. Repairing radiators – For private vehicles, don’t do this even if it’s cheaper it will kill your car eventually, repairing radiators require hot lead to be soldered to the fins or walls of the radiator, the heat can degrade the strength of the metal around the radiator so don’t be surprised if you get leak after leak following a repair. Replace your radiator once it starts leaking or on the advice of your dealer’s service department.


Learned something? Now, relegate your uncle to gardening.
Stant 10227 Radiator Cap – 13 PSI

Stant 45878 SuperStat Thermostat – 180 Degrees Fahrenheit

1 comment for “Four Malpractices That Can Cause Overheat

  1. R. Rawlings
    April 7, 2014 at 7:16 pm

    Cooling systems are very simple, and determining when you are having over heating problems will tell 95% of the story. First things first… The entire cooling system only consists of a few simple things, a radiator, a water pump, a thermostat, a couple of pulleys, a fan belt, a fan and a coolant recover bottle. Keep in mind, horsepower makes heat. With that, let’s go with the most common heating problem first. In street rods and performance cars, the single most common heating problem is when idling in traffic or sitting in the drive-thru waiting for your burger and fries. If a car heats up while sitting, but not when it drives down the road, it is telling you something. What it is telling you is that when driving down the road and the engine is under a load, the cooling system is doing its job just fine, but when the engine is simply idling and has no load on it, it overheats. The main difference between driving down the road and sitting still is the amount of air coming into the front of the vehicle and getting through the radiator. When you drive down the road, (after about 25MPH or so) the air being forced through the radiator exceeds what the fan can pull through. So in essence, after about 25 or 30MPH, the fan is pretty much useless. With that, below 25 or 30MPH the fan is the only thing pulling air through the radiator, and is also the single most common problem with cars running hot in traffic. You have to look at a few things. First; is the fan big enough to draw enough air through the radiator at an idle to let the radiator do its job? Second; is the pulley the right size to allow ample fan speed at an idle? Power pulley kits spin the fan slower to make the horsepower gains, and slower fan speeds mean less air being sucked through the radiator. Third; is the fan close enough to the radiator? If not, get a spacer and get it closer. A shroud may also be needed of you can’t get the fan close enough to the radiator. Pretty much, those are the only causes and fixes to cars that run hot in traffic.
    Now, let’s say your car runs cool at an idle but runs hot when driving down the road or when pulling hills. Well, the first thing to check is if the radiator is full. Radiators don’t work when they are partially full. The second thing would be to make sure it isn’t clogged. A radiator can’t do its job if it can’t flow enough water. It may be too small of a radiator for your engine. You can’t expect a stock radiator, that was designed for a stock engine, to keep a serious performance engine cool, so make sure your radiator is large enough to do its job. Another thing to look for is the water pump. It may not have the water flow capacity to keep your engine cool, so a new high flow pump may be needed, OR, possibly one or more of the impellor blades have rusted off or the impellor itself is slipping on the shaft and not moving the water it needs to move. Another thing to look for is the lower radiator hose. The lower hose should have a spring inside of it. This is because the bottom hose is the suction side, where the water pump sucks water out of the radiator and pushes it through the engine. When the spring is removed or it simply rusts and disintegrates, this leaves nothing to prevent the hose from collapsing under the suction of the pump. If the hose sucks closed, it cuts-off the water supply to the engine. This is easy to check. All you have to do (with the engine off) is reach down and squeeze the hose. You should not be able to squeeze the hose closed. Sometimes the spring inside gets sucked-up inside the water pump inlet a few inches, which exposes a few inches of lower hose to be vulnerable to being sucked closed, especially after the engine has warmed-up and the hoses become even more soft and supple.
    If your engine overheats on occasion OR all of the sudden just started heating-up, this indicates a sticky or stuck thermostat. The fastest way to check for this problem is to start the engine, and let it warm-up and observe the temperature of the upper hose with your hand. If the engine gets warm but the upper hose stays much cooler than the engine, it is telling you that no water is passing through that hose. If the engine is hot, then the water in that hose should also be hot. If not, it’s because the T-stat is closed and it isn’t allowing any hot water to get out of the engine and into the radiator. The second easiest test is to simply remove the thermostat and test drive the car. It will most likely run cooler, and if it does, then it’s telling you it was the T-stat stuck shut. In text books, you’ll read that by removing the T-stat, the engine will run hotter because the water passes through the radiator so fast that the radiator doesn’t have time to cool it down. I have to tell you… this isn’t my first day. I’ve been doing this for about 30 years, and to this day, I have never seen an engine run warmer when the T-stat was removed… NEVER. They have always ran cooler for me, and this goes for every Chevy, Ford, Chrysler, flathead, in-line, pancake, stock, performance, race or whatever kind of engine you can think of, and we’re talking hundreds and hundreds of cars and trucks, not a just a couple.
    Now; for you guys that want to “believe” an engine will run warmer when the T-stat is removed because you think water flows through the radiator too fast and won’t have time to cool, I have a few things to say. Think about it for a moment. What happens when you remove the T-stat? You increase the water flow. If water is flowing too fast through the radiator to get rid of the heat, remember that the cooling system a closed loop system which means the water is also passing by the heat source inside the block too fast to pick-up too much heat. Just remember, for every action there is an equal reaction. Second; If increasing water flow through the cooling system is so bad and causes an engine to run hotter, then please go ahead and enlighten Edelbrock, Stewart, Weiand, and all of the companies that make HIGH FLOW water pumps to cool engines down more than standard flow pumps do, because obviously they don’t know what they are doing then according to your logic. If decreasing the flow & speed through the radiator was the key to cooling an engine, then don’t you think that maybe all of the companies that make aftermarket water pumps would make low flow pumps instead of high flow pumps? But they don’t now do they? No, they make high flow pumps that increase the water flow, speed, & volume. Well, by removing the T-stat, you are removing a restriction in the system which will now make the water flow faster and with more volume. Just remember; ALL a T-stat does is keep the water from flowing so the engine will warm-up faster so your heater will work quicker, and so the engine will warm-up and run more efficiently. Once that T-stat is open, if your engine wants to run warmer, it will continue to rise until the engine reaches its normal running temperature. All it means is the engine cannot drop below what the T-stat is calibrated at, so if it is a 160 degree T-stat and your engine wants to run at 200, then it’s going to run at 200 degrees no matter what. All the 160 degree rating means is that the T-stat won’t open to let water flow through the engine until it reaches 160 degrees. Remove the T-stat and you remove a restriction, which will cause the engine to run cooler just like a high flow water pump will when it “increases” the flow.
    When you have an engine that doesn’t warm-up as fast as it used to in the mornings, then it’s telling you the T-stat is probably stuck open, and isn’t allowing the water in the engine to warm-up fast enough anymore. With thermostats always remember to install it correctly! The side with the spring goes into the motor. If you install one upside down, (with the spring facing up, or towards the radiator) it will take too long for it to open and the engine will overheat before the T-stat opens.
    Let’s say your engine runs cool for a few days, and then starts running warmer and warmer until it finally starts running hot and you have to add water. This is usually caused by not having a water recovery bottle or by not having a proper radiator cap for a recovery system. On cars equipped with nothing more than a puke tube for the water to just dump-out, onto the ground, here’s what happens; each time you run the engine, the water expands, which causes the radiator cap to open at its given pressure setting and puke some water on the ground. Let’s say your radiator holds 3 gallons of water. The first day you run it, you puke-out a cup or so of water. The next day, you puke a couple of more cups. After a few days of this, you have puked-out a half gallon or so of water from the radiator. Now you only have 2 1/2 gallons (or less) of water in there. With less water, the engine will start to run a little warmer, which in turn causes even more heat and expansion, and even more water to puke out of the radiator. Now you are down a gallon or so of water, and guess what, the engine starts running warmer each day you drive it until you simply over heat and have to add more water.
    A coolant recovery bottle saves the water being puked out of the radiator and when the engine cools down, it sucks all of the water back into the radiator again, so you don’t actually LOSE any water. It just passes back and forth instead of being dumped and gone forever. If you don’t have a coolant recover bottle (aka a radiator overflow bottle), then you should get one.
    Another cause for an engine to run warm is if the timing is too far retarded. Every 10 degrees of timing, can cause a 10 to 20 degree difference in heat. When the timing is too late (retarded), it will also cause the headers to glow red.
    If you just built an engine (especially a Ford or a late model Chevy), and you are having overheating problems from the start, you have to make sure you installed the head gaskets pointing in the right direction. Some engines only have water passages on one end of the head gasket. If one (or both) of these gaskets get installed facing the wrong way, it blocks-off the water flow and you’ll have an instant overheating problem, and the only way to solve it is to remove the heads and replace the gaskets with new ones, facing the right way.
    For you Early Mustang people out there, there is an old tale about 289’s and 302’s running hot when bored-out. Factory spec is up to .060” and in 99% of all cars, that is just fine and will not present any heating problems. In 65 and 66 Mustangs though, it is taboo. It isn’t the engine’s fault though it’s the crappy radiator support’s fault. Have you ever noticed that 4 row radiators are extremely common in early Mustangs? You don’t see Camaro’s or Chevelle’s needing 4 row radiators, or 67/68 Mustangs needing 4 row radiators. You don’t see little 289’s in early 5,000 Lb Galaxies needing 4 row radiators do you or late model 5.0 Mustangs needing 4 row radiators? The reason for this is the width and design of the early Mustang radiator support. The first problem is the size of the radiators those cars have. They are very narrow and short compared to just about any other car out there. That’s why the aftermarket “performance” versions go 3 and 4 rows thick, rather than going wider. Well, this doesn’t always solve the problem. What needs to be done is to cut-out the radiator support and fit a radiator that is wider, such as one from a 67 or 69 Mustang. This allows for more cooling surface area and more capacity of coolant. The second and probably even more important thing wrong with these cars is the location of the radiator hose inlets and outlets. If you look at one of these cars, you’ll see that the upper and lower radiator hoses are right in-line with each other. This is about the worst thing you can have. The water only flows down the one side of the radiator and leaves the rest just sitting there. I mean, think of it like this, why should the water flow through the rest of the radiator when it is being dumped in and out of the same side. This is why cross flow radiators were invented. You don’t see cooling problems in later model 5.0 Mustangs do you? It’s the same engine, so if there was a problem with the engine itself, these cars would have it too. These cars also have the same cooling capacity, the same water pump (although reverse rotation) and so on, so it isn’t like they are totally different. They are very much the same indeed, yet one has a serious cooling problem and the other doesn’t, so how could that be the engine’s fault? It’s because the radiator inlets and outlets in the 5.0 Mustangs are on opposite sides of the radiator which forces the water to utilize the entire radiator’s surface for much more efficiency. Again, don’t blame the 289/302 or listen to wives tales created by someone who obviously didn’t know what they were talking about. If 289’s and such had that bad of a heating problem, then 1: Ford would have re-designed the cooling systems on these engines for the later model 302’s and 351W‘s, (which they didn’t because there is no problem to begin with), and 2; Larger, heavier cars with the same engines (like big old Galaxies or trucks) would have even worse problems, and that simply isn’t the case. It’s only the early Mustang’s with the cooling problems, so it obviously isn’t the engine’s fault for being bored oversized or for having a cooling problem.

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