Results 1 to 5 of 5

Thread: Cooling Systems - Overheating Problems.

  1. #1
    Just Another Part Time Grease Monkey
    Join Date
    Apr 2006

    Default Cooling Systems - Overheating Problems.

    Several people seem to be having overheating problems I thought a comprehensive new topic might be worthy. Thanks to those who have helped others with their problems as I have included your suggestions here as well. Some have been missed, some have not been made so please add your comments.

    Before spending $$$ fixing an overheating problem it is best to make sure you actual have one first.

    Symptom 1.
    Make sure your gauge is reading correctly. Does the engine itself feel hotter than normal? Can you get another measuring system? One of those infrared pyrometers is good for diagnosis, but maybe a bit expensive. Stick on strips, which have square that change colour over the temp range – I have seen some going from 70degC to 110degC with 4deg increments and must be relatively cheap (maybe one for the engine and one for the radiator).

    Is it the gauge? If the sensor is disconnected under the bonnet will the gauge go down and then go all the way up when earthed onto the engine. Check this before buying a new sensor as it will also make sure you are replacing the correct one.

    If everything is reading correct and you have a problem then read on.

    Symptom 2.
    If you just lost a bunch of water, was it just caused by the water level being just a bit too low? Fill the system up with coolant again and see if the problem remains. Some cars are not so easy to fill due to air locks in the system and the radiator being low at the front of the car.
    1. Make sure the heater is switched on.
    2. Angle the front of the car up a hill so air ends up in the radiator.
    3. Only tip cold coolant into a cold engine or slowly into an idling hot engine to prevent cracking the head.
    4. The engine will need to be running to get the last of the air out of the system since the moving water should push the air out.
    5. To ensure there is water in the heater (not air) ensure it is getting hot. If not you might need to pull the top hose off the heater valve and tip some coolant in there. This will also let the air escape

    Hopefully when full there will be no problem, but if you continue to lose water then the problem needs to be sorted. Check for leaking hoses, water pump, heater core and poorly tighten clamps. Then consider the blown head gasket issue.

    If you assured the car is actually getting hot and there is coolant in the system you can look at troubleshooting the issue.

    What Next.
    If the engine is actually getting hot you need to consider what the basic requirements of the cooling system are:
    1.Coolant (of good quality) must fill the engine and radiator
    2.Engine Cooling - water must be getting circulated from the engine to the radiator.
    3.Water Cooling - the water in the radiator must be cooled sufficiently by airflow.

    Replace the thermostat with one in a fully open position (read below). Get the fans to run full time and then take it for a drive to see the car still gets hot.

    If it does not get hot then you can reinstall the thermostat to see if the problem remains. Maybe you need a colder thermostat. If the run was OK then see what happens when the thermo-fan switch is reconnected.

    Before the thermostat opens water is sent via a bypass circuit, which helps the engine to warm up evenly and maintain a constant temp across all cylinders– without the bypass, one part of the engine might be really hot before the thermostat starts to open. When the thermostat opens (allowing water to the radiator) it starts to block off flow through the bypass circuit with the back of the thermostat. If the bypass circuit is not blocked off by the thermostat when the engine is hot, it is possible that not enough water will not go through the radiator to be cooled.

    Coolant Quality.
    A lot a workshops will use the brand of coolant is recommended by the car manufacturer for their own liability. There has been the claim that certain alloys used for cylinder heads by manufacturers are not compatible with any other brand of coolant than their own brand – who knows. I have come across one guy who claims to have tested all the coolants on the market so he could feel happy selling it but since nothing came up to his standard he got his own made.

    Coolants have various attributes. Some of these are:
    1. Glycols heat transfer ability is worse than water, so a higher percentage means worse performance.
    2. Some coolants have a detergent in them to “wet” the surfaces and improve the water contact. I have seen a brand that after being placed in a 600ml cool drink bottle and shook took a long time for the bubbles to get to the top. The problem here is that your pump will start pushing a percentage of bubbles, rather than water, around the system. If the bubbles accumulate in the head not heat can be removed from that area.
    3. Colour changing coolants only change colour after they have been harmful to your system. It is best to change all coolants once a year.
    4. Some allow build up of scum inside the system.
    5. Additives raise the boiling point of water – good thing.

    Engine Cooling Troubleshooting Points.
    For an engine in standard form with relatively standard output the OEM water pump and thermostat should be up to the job. You just need to make sure they are both working properly.

    Before installing a new pump make sure the impellor and pulley are not going to spin off the shaft. Once installed make sure it can still spin freely. IMHO the pressed steel “impellor” is not actually able to move as much water at the high rpms (due to cavitation) as it does at normal RPM. I have had a hand made one fitted with closer tolerances to the wiping face, which looks a like more like one you would see in a non-automotive water pump (curved and tapered fins etc). In this case you can find/make a better impellor, which will actually move the water, change the drive pulley size or take the normal route and fit an electric pump to move the water around.

    If your pump and thermostat are working once the engine heats up you should feel the radiator hose warm up. Before installing a new thermostat check to make sure it opens by placing it in a pot on the stove with a thermometer. Place the thermometer and thermostat in the pot while cold and let it warm up over the heat.

    The optimum setup is to find the best speed and type of fluid to pump through the engine for maximum heat (and steam) removal, and then maintain this throughout the rpm range. The water temp across the engine (via the bypass circuit) could be kept as high as safely possible (since it would be even) with a varying amount sent to the radiator to maintain that temperature.

    If the water pumping through the engine is insufficient to absorb the heat then a temperature difference across the engine is introduced from where it enters to where it leaves, resulting in localised boiling. Fixing this using bigger, more efficient radiator cores just reduces the overall temperature, but does not address the temperature difference.

    Water Cooling Troubleshooting Points.
    1. Is the radiator blocked – remove it and take to shop for a quick flush. Normally not too expensive if you do the removal/install.
    2. Radiator, a/c condenser and/or FMIC blocked to air flow from bugs, grass, too many bent fins etc.
    3. Make sure air is flowing through the radiator front to back the same direction. Sometime thermo-fans can be wired incorrectly blowing air the other way. Put a piece of paper in front of the fan and make sure it is getting sucked in the right direction. If it is wrong try to reverse the polarity.
    4. Neatly fitting shroud around the fan blades and between the radiator and its supports to make sure all the air you want to send through the radiator is actually travelling through it.
    5. Sealing around the edges of the shroud and radiator might be required.
    6. Ensure the thermo-fans are they turning on at the right temperature, if at all. This may be more likely if overheating occurs at low speed since at higher speed the motion of the car should solve the problem.

    Head gasket / Head leaking.
    Bubbles coming out of the radiator are a bad, but not definite sign, especially if the engine is cold. When the engine is hot, localised boiling of the water inside the head (mainly around the exhaust port) causes the system to pressurise. Normally this will be absorbed back into the water, but could be incorrectly interpreted as a blown head gasket on a hot engine.

    Head gasket options (more likely than cracked head).
    A compression check is always the first thing done if the head gasket is suspected, but also reflects the condition of the valve seating and piston ring condition - so it is not definitive.

    There are three separate systems inside the head being oil, water and the combustion chambers. Usually it will be the water communicating with either one or both the others.

    Water to Oil – you will get milky oil and the water level will drop causing overheating. Also might see oil in the radiator. Either way the head is coming off.

    Water to Combustion Chamber – will cause bubbles in the radiator from gases in the combustion chamber (can get a teekay test done). You will also get moisture going the other way when the engine is not running. To test this you can insert a cold screwdriver into the sparkplug hole on each cylinder of a warm/hot engine that has just been turned off. After a couple of minutes remove the screwdriver. If there is moisture you will see condensation on the screwdriver and know the head needs to come off.

    Another method is to look for condensation on the spark plugs once removed, but it is more likely to collect on something cold.

    If all other options have been exhausted then a crack between the cooling system and the exhaust port has been seen, which would not show up in the above tests. In this case a pressure test of the cooling system might actually give reason to remove the head and send it off for a full pressure test.

    Backup Warning System.
    To try make sure I do not cook my engine I have purchased a thermostat switch from Jaycar (part number ST3825) which closes the circuit at 100degC. With the addition of an electronic alarm buzzer (mounting under the dash) I plan on mounting the switch (with glue) onto the alloy housing of the return from the radiator (normally 88degC) such that if it ever gets to 100degC I will know immediately.

    This is a backup system in case, I, or whoever is driving my car don't notice the gauge or blow a hose and the gauge won't show me the engine is about the seize. For under $10 is must be worth it.

    There are normally closed ones rated for 70 and 90 degC (ST3825) which might be a good temporary replacement for a thermoswitch since they cost only $4.45 each. I have seen them in use for that very purpose.

  2. #2
    serial biochemist Automotive Encyclopaedia
    Join Date
    Apr 2006
    South Australia

    Default Re: Cooling Systems - Overheating Problems.

    great post. covers a number of important points for people with heat problems. good work!
    your rep rating is not a reflection of your worth to the community

    Quote Originally Posted by H1TMAN
    wtf? I want to do track racing, and f#@k you...
    that's very flattering but no thanks.

  3. #3
    JZ Powered Too Much Toyota EldarO's Avatar
    Join Date
    Oct 2005
    Western Aus

    Default Re: Cooling Systems - Overheating Problems.

    great post, ill also add, toyota red coolant FTW!


  4. #4
    Gobble, Gobble! Automotive Encyclopaedia mrshin's Avatar
    Join Date
    Nov 2005

    Default Re: Cooling Systems - Overheating Problems.

    Another thing, many mulletmeters come with a thermocouple - slip one under a hose, it's a handy way to keep an eye on temp when you want to.

  5. #5
    Low rep
    Join Date
    Feb 2006

    Default Re: Cooling Systems - Overheating Problems.

    Great post! That own help anybody !

Similar Threads

  1. Sam-Q's 20V RWD Cooling System Guide
    By Sam_Q in forum Engine & Driveline Conversions
    Replies: 14
    Last Post: 27-03-2007, 06:08 AM
  2. 4AC Problems....
    By Rallystanza in forum Tech and Conversions
    Replies: 16
    Last Post: 04-02-2006, 10:36 AM
  3. MA70 heating problems.
    By EldarO in forum Tech and Conversions
    Replies: 50
    Last Post: 02-02-2006, 02:35 PM
  4. Overheating problems. 7M-GTE
    By 7mSupra in forum Tech and Conversions
    Replies: 20
    Last Post: 04-01-2006, 12:01 PM


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts