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Thread: Missing coolant (aka, well crap...)

  1. #1

    Missing coolant (aka, well crap...)

    I haven't driven the 4Runner for 2 weeks so this weekend I decided to give it a bit of exercise and figured I'd do a quick fluids check first. It turns out the radiator overflow tank is bone dry, and looking in the radiator cap I didn't see any fluid. Obviously this is not a great thing to see. The truck also been loosing some oil recently, which I think is due to a leaky valve cover gasket.

    The oil on the dipstick looks normal and not milky, so I'm really hoping this is not something dumb like a blown head gasket (truck only has 110k miles), and instead suspect a coolant leak somewhere such as the rear heater lines. So, the plan is to remove the skid plates, put some water in, bring things up to temperature and look for leaks. As a precaution I'll also pull a couple spark plugs and look for any signs that coolant is getting into the combustion chambers. Any other suggestions on how to debug this?

    - Matt
    2000 4Runner Sport / 4x4 / 5spd / E-locker / SS 1.2 / 265x75x16 Bighorns / ARB Prado / HD-SKO

  2. #2
    Your year isn't really prone to head gasket problems so probably not that. I could be hoses, but I'd guess water pump. Check the weep hole, there might be crusty red stuff around it.
    -------------------------
    Steve
    1993 4runner, SAS, 3.0L, Auto Tranny
    2007 4runner, stock. For now.

  3. #3
    Our engines aren't know for HG problems but it's not unheard of and does happen. As far as leaking do you or do you recall smelling any coolant? Our Subaru had a pin hole leak on the top plastic of the stock radiator and I could smell it 10 feet away. It was small enough I wasn't too concerned but did watch it while a new radiator was ordered.

    Two weeks is a while but a leaky heater core may wet carpet in the cabin so run the heater and check the carpet. In two weeks if it did leak I'm sure it's dry but maybe check for discoloration or smell in the carpet near the firewall/footwells.

    Keep us updated.

  4. #4
    I haven't owned a Toyota truck yet that would keep any measureable amount of fluid in the overflow container.

  5. #5
    I've had the IAC gasket go bad and burn up coolant that way. It was extremely slow, but it would empty out the overflow tank pretty often.

    Ken, I had that problem for a while, but now my tank stays where I fill it to. Not sure what I did different, but it seems to be working.

    I would look for some external leak in the cooling system, likely a pinhole in the radiator or hose (have the hoses ever been changed with such low mileage?) or heater core.
    2005 Lexus LX470 - Stock for now...

    1998 Toyota 4Runner SR5 V6 4x4 + a bunch of goodies. Lifted, Locked, Illuminated and Armored. Winner,"Best Offroad Truck" - 2010 Pismo Jamboree. It's been upside down and still drives me to work.

  6. #6
    The overflow tank has always baffled me. It gets filled when the radiator gets hot enough and has enough pressure to push the cap up and have fluid pour into the bottle. To me if it's empty it's not a big deal. Right? Fluid can't get back to the radiator as the overflow is not pressurized and even if it were the radiator cap acts like a one way valve most of the time. I know some European cars are different but our Subaru and the 4Runner are as I described.

    Matt, I think that if you had a leak you'd see or smell it as the truck has not been moved for 2 weeks. Even if it happened coming down the mountain I think you'd pull into your parking spot hot and pressurized.

    Have you opened the system recently? Like Sean mentioned, the IAC has coolant lines to at albeit small and at the highest point of the system.

  7. #7
    As far as I know, the "overflow" tank supplies coolant back into the system as it cools, and should always at least cover the bottom of the tube when cold. There are low and full marks on the bottle as well. Maybe I misunderstand that process, but that was always my assumption.
    2005 Lexus LX470 - Stock for now...

    1998 Toyota 4Runner SR5 V6 4x4 + a bunch of goodies. Lifted, Locked, Illuminated and Armored. Winner,"Best Offroad Truck" - 2010 Pismo Jamboree. It's been upside down and still drives me to work.

  8. #8
    Not to totally hijack Matt's post but I thought it worked the same way Sean. Except when you think of it how can the bottle supply the radiator? I guess under some kind of vacuum the radiator could suck it back in but the radiator is a pressure vessel or sorts. The inlet to the over flow hose is also between the seal of the radiator cap and the bottom of the cap which is held in place by a spring. As the vessel gets hot, it pressurizes and pushes up the spring to allow overflow. To get it flowing the other way is a mystery to me.

    Edit: Mystery solved?
    http://auto.howstuffworks.com/cooling-system7.htm

    I guess it does pull a vacuum. The "other" spring was something I didn't know about. I don't think I've even been able to keep an overflow bottle with coolant in the Toyota or Subaru. My Chevy truck could but that tank was well over a gallon.
    Last edited by 4x4mike; 04-22-2014 at 12:31 PM.

  9. #9
    Actually, inspect the hose system and bottle for cracks or leaks. It might be a non pressurized part leaking, especially since you haven't had an overheat. On my friend's '82 3/4ton, his overflow bottle disintegrated because after driving home every day, his dad, and then him, opened the hood to cool the engine off. What saved most of the underhood parts ruined the bottle, since it was not UV stable.
    2005 Lexus LX470 - Stock for now...

    1998 Toyota 4Runner SR5 V6 4x4 + a bunch of goodies. Lifted, Locked, Illuminated and Armored. Winner,"Best Offroad Truck" - 2010 Pismo Jamboree. It's been upside down and still drives me to work.

  10. #10
    Quote Originally Posted by 4x4mike View Post
    Not to totally hijack Matt's post but I thought it worked the same way Sean. Except when you think of it how can the bottle supply the radiator? I guess under some kind of vacuum the radiator could suck it back in but the radiator is a pressure vessel or sorts. The inlet to the over flow hose is also between the seal of the radiator cap and the bottom of the cap which is held in place by a spring. As the vessel gets hot, it pressurizes and pushes up the spring to allow overflow. To get it flowing the other way is a mystery to me.

    Edit: Mystery solved?
    http://auto.howstuffworks.com/cooling-system7.htm

    I guess it does pull a vacuum. The "other" spring was something I didn't know about. I don't think I've even been able to keep an overflow bottle with coolant in the Toyota or Subaru. My Chevy truck could but that tank was well over a gallon.
    i love how stuff works. i remember reading the article on how an IC engine works back when i got my 4runner (first car) and it was a big reason for me getting interested in maintenance/DIY/modding to begin with.

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