Edmunds Answers



  • zaken1 03/29/11 11:13 pm PST

    If the radiator has become restricted from deposits; it could cause overheating. So would a radiator cap that did not hold pressure, or which had a lower pressure rating than the original 16 psi cap. A leaking radiator or heater hose will also cause the motor to heat up. A defective fan clutch would cause a tendency to run hot; as would having removed the original fan shroud. A defective water pump, or a loose water pump drive belt will also lead to hotter running.

    Using 100% undiluted coolant will also cause overheating. Coolant is engineered to be mixed with at least 30% water (preferably distilled water), in order to transfer heat out of the engine effectively.

    Many companies produce thermostats for this motor in both premium and economy models. The premium models operate more stably and respond faster to heat input than the economy models. Thermostats also are available in three different temperature ranges; 195 degrees; 180 degrees; and 160 degrees. The cooler thermostats will be less likely to lead to rising temperature; expecially if the radiator is partly clogged. There are also different design radiators available; the heavy duty radiators will cool better than the light duty ones.

    In order for the engine to be coolest; it is important that the coolant reservoir tank is in place, is kept properly filled with coolant mixture, and the hose from the radiator to the reservoir is undamaged and free of leaks. Modern cooling systems are designed to be used with the radiator always filled to the very top. If the coolant level in the radiator is not kept absolutely full; the siphon between the radiator and the reservoir will not work. In that situation; the level in the radiator can drop; while the reservoir level remains full. This can lead to serious overheating, if the radiator cap is not removed to check the level. Also; whenever any parts are replaced in the cooling system; there is bound to be trapped air left in the system. The air will gradually work up to the top of the radiator during the first few days after the system is refilled; which will leave the coolant level low in the radiator. This is why it is necessary to recheck and refill the radiator at least three times after initially filling the system. If the level still is not found to be full on the third check; keep checking the level on subsequent days until the level either stops dropping; or the leak is discovered.

    A leaking cylinder head gasket can also make the motor heat up; as well as causing a loss of coolant without there being an external leak. Repair shops can pressurize the cooling system and quickly find out if there is an internal or external leak.

  • greatestmind 03/30/11 3:05 am PST

    Start your engine and let it run and when the temperature gauge begins to rise beyond half way, see if the fan come on. If not there's your problem or at least part of your problem. If so, now being very careful to avoid the fan, feel the large inlet radiator hose along with the large outlet radiator hose. Do they feel the same temperature, or is one cooler than the other. Report back.

  • zaken1 03/30/11 1:21 pm PST

    Dodge pickup trucks do not have electric radiator fans; so you can ignore the previous bit of advice about that item.

  • greatestmind 03/30/11 2:35 pm PST

    If you look at my statement more carefully you'll notice I never said the type of fan, whether it be Electric or Thermostatic. All I mentioned was the fan coming on, and no matter what type fan it is, it will still come on at a certain temperature. So unless you're ready to say it doesn't have a fan because it is not electric, please do not indicate that I don't know what I'm talking about. Afterall I thought we were supposed to be on the same team, trying to help someone with car troubles, not letting them see us battling over information. I would have said, "in case it doesn't have", or "also check to see", not disregard the previous information. Believe me, I'm not in competition with you or anyone else, only trying to help someone. This is not about you me, and in the end I stand by my information, and putting the type fan aside is the procedure correct?

  • zaken1 03/30/11 9:32 pm PST

    The reason I disputed your response is that there are only two non-electric types of cooling fan drives used on belt driven fans; thermal and viscous. And neither the thermal nor the viscous fan clutch has a definite temperature point at which it "comes on" when the motor is idling. There is enough friction in both of those clutches that they will rotate the fan at idle as soon as the motor begins running, even when it is cold. Granted; at higher engine speeds; a clutch which has activated will transmit more power into the fan than it does when cold; but the average person cannot notice from looking at the fan rotation whether the clutch is "on" or "off" while the motor is idling. In my experience, your description of "checking whether the fan comes on when the temperature gauge gets about half way up the scale" is only applicable to electrically controlled fans. This type of test cannot be done on a Dodge pickup. And that's what led me to criticize your response.

    I, too, am mainly interested in fixing people's problems. Because of this; I typically don't say anything about people's mistakes in grammar, spelling, or word usage; since it does not mislead people about the technical information they seek. But when an answer comes across as misleading; I feel it is important to point that out to the person who asked the question. But I can only use my own perceptions to gauge whether to criticize an answer. The person who wrote the response is not by my side when I write; so once in a while; we will have a difference of opinion.

    The amount of misleading and innacurate information posted on this site both messes up people's efforts to fix their cars; and also reduces the credibility of this site. I have seen many caring people who contribute here point it out when they see something that sounds wrong to them. If you don't think that is a good thing to do; you're entitled to your opinion; but I, too, am entitled to do what I think is right.

  • 0patience 03/30/11 10:49 pm PST

    Actually, the 5.9L (which I assume is the engine he has) has a viscous fan with a thermostatic spring, which are prone to failure.

    The fan drive clutch is a fluid coupling containing silicone oil. Fan speed is regulated by the torque-carrying capacity of the silicone oil. The more silicone oil in the coupling, the greater the fan speed, and the less silicone oil, the slower the fan speed.
    The fan drive clutch uses a heat-sensitive, coiled bimetallic spring connected to an opening plate. This unit causes the fan speed to increase with a rise in temperature and to decrease as temperature decreases.
    If the fan is not working properly, it will cause it to over heat.
    To check the clutch fan thermostatic spring, disconnect the bimetal spring and rotate 90┬░counterclockwise. This disables the temperature-controlled, free-wheeling feature and the clutch performs like a conventional fan. If this cures the overheating condition, replace the clutch fan. If it does not cure the overheating problem, re-connect the spring and check cooling system.
    You can also check the fan by checking to see if it will move laterally. Meaning if you take the fan blades on each side (engine NOT running of course) and see if it will move. If it does, then the bearing may be failing.
    Then turn the fan blades by hand (again, not running) and there should be some resistance in turning the blades. If there is not, the fan hub has failed or is failing. This movement should not exceed 1/4 inch (6.5 mm) as measured at the fan tip. If this lateral movement does not exceed specifications, there is no cause for replacement.
    I've had to replace a bunch of these fan hubs.

  • greatestmind 03/31/11 2:02 am PST

    Can I again state that I was more interested in water circulation than fan operation. I'm not familiar with every type fan in every car, but I am familiar with coolant system operation and I was really trying to lead him there (maybe water pump). Some radiators have caps where you can see the water circulate upon the thermostat opening and some do not. Because I wasn't familiar with the components I spoke in general which you can do sometimes like setting ignition timing by engine pitch when you don't have a timing light. STREET MECHANICS.

  • zaken1 03/31/11 2:39 am PST

    When trying to answer questions about vehicles I am not familiar with; I have found that first looking up the parts on that vehicle in an online parts catalog (like www.rockauto.com) has saved me from posting serious mistakes time and time again. Even then; I still run into unexpected issues often enough that I have learned to avoid writing about things which I don't know well. Starting many years ago as a street mechanic like yourself, I also became good at setting ignition timing by ear. But I then learned that it is very difficult to set timing by ear precisely enough to pass emission tests (which will fail a car if the timing is even 2 degrees off the factory spec). So I had to start using a timing light; even when I thought it was not necessary. This whole path has been a growth process; but the things which led to the most growth were sometimes the things that were most uncomfortable for me to face at first. Curiosity, a thirst for information, a love of reading manuals, and the willingness to face and accept the value of constructive criticism have done more for me in my 40 year career as a performance tuner, diagnostic specialist and shop teacher than anything else.

  • greatestmind 03/31/11 2:59 am PST

    Once more I'm going to respond than quit. It doesn't take a rocket scientist, or a bunch of diagnostics technology, or whatever to understand a simple request, feel the temperature of two hoses. This has gotten way out of hand and I do apologize for any confusion I may have caused. ( I felt some test could be spoken to him in basic layman terms.


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