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Cooling Systems -- Problems & Solutions (Radiator, Fan, etc)



  • kiawahkiawah Posts: 3,666
    Coolant leaks typically could be (in no particular order):
    - heater core inside car, typically you might smell antifreeze in cabin, passenger carpet wet, or windows fog up
    - engine head gasket, allows coolant to leak into cylinder, get's burned up when car start and comes out as vapor out the exhaust. Can ruin cat converter, and of course water in engine is not good.
    - water pump, could drip around shaft
    - any and all hose connections, as previously mentioned
    - radiator core, sometimes obvious, sometimes pin holes will drop so little that the air flow vaporizes and hard to find. Could also leak internal into transmission cooler section, disaster for transmission.
    - cracked overflow container, or hose to the container.
  • Thanks for your detailed reply!

    From your list, I think I shall check the overflow container and the water pump first.

    If it is a leaking water pump, approximately how much should it cost to replace?
  • fullerrufullerru Posts: 1
    Greetings friends

    I've been having a slight problem with my 1998 toyota mark II - 1G-FE 1988cc engine.
    Here it goes: whenever I pressure the car (drive real hard) or use the ac the temperature gauge rises and will continue to rise to even red zone if I dont ease up. When this happens the radiator loses no coolant nor does it boil, it just seem to be cool and normal and i never have to top it up...ever.
    The radiator have been removed, flushed and rod out, cap has been changed, clutch for fan replaced and also the thermostat has been replaced but still the problem remains.
    I am now suspecting that the problem is stemming from either a faulty coolant temperature sensor or temperature switch, however, i've looked for a temperature switch where I know they are normally located (at the exit or inlet goose-neck where the hoses are connected) but cant seem to locate it.
    Can anyone offer some input on this problem or help me locate the temp. switch or temp. control unit on this car?????
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,416
    You mean, by "switch" the fan sensor as opposed to the gauge sensor?

    If your fan turns on during this "overheat" then no sense chasing the fan switch/sensor or the relay.

    I'm sorry but we don't see this engine in the USA, so I can't locate the part---unless you know of some older US model that might have used it.


  • Hi everyone,

    I hope someone can help me out. I have a 99 Chevy silverado, 5.3, 4 weel drive. Started overheating so flushed out radiator and changed thermostat. Next day, still over heating, replaced water pump and verified fans are working. STILL overheating, The BIG question, WHAT'S LEFT??? Any one know what steps I am missing? Any help would be great.

    Thanks to ya all
  • imidazol97imidazol97 Crossroads of America: I70 & I75Posts: 18,048

    How do you know it was overheating?
    Is the temperature gauge reading high?
    Is the coolant bubbling?
    Is the engine actually above the permitted range?

    Possible factors:

    Temperature gauge reading wrong due to gauge or sensor bad?
    Head gasket leaking?
    Pressure cap not sealing and holding proper pressure allowing the engine to go above the boiling point of the pressurized coolant giving boiling?


    Infrared heat thermometer to see if thermostat area/upper radiator hose are actually above the 230 or so it might reach under pressure in a hot environment.
    Check coolant with a test strip or sensor to see if hydrocarbons are in it from leaking head.
    Clean pressure cap. Check pressure if a cap check device is available. Is upper hose becoming very solid because of pressure--that might indicate the cap is working. I do not recommend opening cap when car might be under pressure warm because of danger from coolant spewing out.
  • Well, have pressure on upper hose, gauge is reading hot, no "Bubbling" in over flow to indicate overheating, replaced thermostat, water pump, chemically flushed radiator, put in fresh antifreeze, new radiator cap. Checking clutch fan to make sure it is working properly.
    I read there is a sending sensor for this year? Is that correct?
    Think the sensor could be bad since there are no other obvious indicators?

    THANKS for any help
  • imidazol97imidazol97 Crossroads of America: I70 & I75Posts: 18,048
    Is there a time or type of driving when it overheats? That might indicate inadequate flow through radiator.

    Have you used a chemical test strip or the sniffer type sensor to check for hydrocarbons in coolant as a worse case possibility?

    Has interior of lower hose collapsed restricting flow to water pump when it sucks the coolant through the hose?
  • I am not familiar with that kind of testing. Actually called chevy shop and for $49.95 they can run diagnostic.
    The "Worse case" possibility is what? I have exhausted my knowledge at this point. Granted, I am no mechanic either.
  • imidazol97imidazol97 Crossroads of America: I70 & I75Posts: 18,048
    Shops use a tailpipe type sniffer that senses hydrocarbons coming from the coolant. That indicates a combustion leak into the coolant, typically a head gasket. There also are test strips that can be dipped into the coolant to sense hydrocarbs that I've heard mentioned on car repair programs on radio.

    Radiator shops do a flow test on radiators to see if enough coolant can flow through the radiator.

    If the lower radiator hose is somewhat soft after years, it might have the inner layer pulling away from the outer part and partially blocking the flow of coolant from the radiator.
  • OK You have helped alot. Just 2 questions, How hard is it to change head gasket?
    How can you test the lower hose for integraty?

    Very thankful for your input
  • imidazol97imidazol97 Crossroads of America: I70 & I75Posts: 18,048
    Feeling the hose is one technique. If uncertain, taking it off and looking at interior is best. By then it's cheap just to go ahead and replace it.

    Does it overheat driving at speed along the highway or roads? Overheat sitting idling?

    Head gasket requires careful diagnosis and checking pressure inside cylinder with compression tester to see if a particular cylinder doesn't maintain as high pressure as next one. It requires removing the intake manifold, valve covers, and then the head bolts. Head needs to be inspected for cracks, etc., that might cause leaking.
  • Just went out and started truck for 2 minutes, let it get to operating range, no change in resistance on fan but let it run idle, not highway. It heats up at highway speeds, not on idle. Felt top and bottom hoses, top felt hot and bottom did not.
    Suggestions on the "Cheaper" way to check for sure?
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,416
    Okay, if it heats up at speed but not at idle you have a coolant circulation problem, not an air circulation problem.

    By the way, a chemical flush of the radiator is a pretty lame procedure---you could still have a clogged radiator.


  • imidazol97imidazol97 Crossroads of America: I70 & I75Posts: 18,048
    Agree with shiftright. Now that you've said it's an overheat at higher speeds, it's back to the radiator and or lower radiator hose.

    The cheapest is to take the radiator out yourself and take it to shop for proper cleaning.
  • just ran it at speed for a few minutes (Actually went on highway for a few miles) The gauge never mooved but after coming back, I felt no resistance change in the fan, is that a correct way to see if the fan clutch is bad or going bad?

    Any idea whats the best way to make sure radiator is not plugged? (No more LAME testings)
    Thanks for your input.
  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,416
    You'd have to pull it out and have it flow-tested.

    Again, if you have high speed overheat, this is probably not a fan problem (air problem).


  • oldfarmer50oldfarmer50 Posts: 6,229
    Ok let's see how smart you guys are.

    1984 Corvette 5.7L with 100+K miles runs hot at lower speeds. Gets up to a 235 temp before radiator fan kicks on and cools things off. Runs normal at highway speeds.

    Am I looking at a sticking thermostat or a defective fan switch or something major?

    2009 PT Cruiser, 2008 Eclipse, 1995 Mark VIII, 1988 GMC Van

  • Mr_ShiftrightMr_Shiftright CaliforniaPosts: 44,416
    If you overheat at lower speeds but not at higher speeds, you have an AIR circulation problem, not a coolant circulation problem.


  • bolivarbolivar Posts: 2,316
    Your car may be running correctly.

    Does it hit 235 before fans with the AC off? Or is your AC dead and not running? The Cadillac referenced below will not let the AC turn on if the AC pressure is low or high.

    In other words, for Cadillas Northstars, if you are running the car with the AC off, it is set to let the temp hit about 225 before it turns the fans on. That's just the way they programmed it.

    If you have the AC working and on, the fans run all the time (above 195 or so??).
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