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Thread: Engine overheating but lower radiator hose is cold

  1. #1

    Engine overheating but lower radiator hose is cold

    I was having issues with overheating and leaking out of the weep hole on my water pump so i replaced a few things. I replaced the water pump along with thermostat. Before I did all of this the engine had overheated but doesnt show any bad signs while driving around afterwards. But Once it gets to the point where the thermostat should open it just keeps over heating. But when I put my hand on the lower radiator hose it cold as where my upper is too hot to touch. Any ideas?

  2. #2

    Re: Engine overheating but lower radiator hose is cold

    how much time are you giving when your warming up the car?
    new thermos need to settle so it will stay closed for a few mins then open up.

  3. #3

    Re: Engine overheating but lower radiator hose is cold

    At first I just let it idle for about 15min but would't go above below middle of the temp gauge. I drove it around taking it no higher than 3.5k. With in 2-3min the temp gauge was pegged up top. When I pulled back into my driveway the overfull was bubbling after i turned it off. Left it cool down added more coolant and started it up again and then it over heated and started bubbling again. It really seem my thermostat isnt opening at all.

  4. #4

    Re: Engine overheating but lower radiator hose is

    It's not opening..there's air in the system, you'll have to bleed it.

  5. #5

    Re: Engine overheating but lower radiator hose is

    I am going through the same stuff right now. Are you absolutly sure you have ALL the air out? Every time I think I got, nope. More issues. Try bleeding some more.

  6. #6

    Re: Engine overheating but lower radiator hose is cold

    a friend with an s14 sr20 had the same problem. The lower hose wouldnt get warm. Replaced the thermo and same thing. when bleeding the system, jack the front end of the car up, when it reaches normal operating temp, put the heater on full blast, then as the bubbles pop out from the radiator top(keep topping off with anti-freeze/water).

    -Also heard from a mechanic to put Asprin in the thermo-stat(keeps it open for faster/easier bleeding). But i never tried it. good luck

  7. #7

    Re: Engine overheating but lower radiator hose is cold

    Also heard from a mechanic to put Asprin in the thermo-stat(keeps it open for faster/easier bleeding).
    Never heard of that one. That's actually kind of a slick idea. If the aspirin tablet can stay intact for a few minutes, it would prop the thermostat open a bit so you dont have to wait for the car to warm up to get the coolant circulating and the bubbles moving. Cool!

  8. #8

    Re: Engine overheating but lower radiator hose is

    Also heard from a mechanic to put Asprin in the thermo-stat(keeps it open for faster/easier bleeding).
    Never heard of that one. That's actually kind of a slick idea. If the aspirin tablet can stay intact for a few minutes, it would prop the thermostat open a bit so you dont have to wait for the car to warm up to get the coolant circulating and the bubbles moving. Cool!
    I tried that too after hearing about it. Good luck, the spring on the thermostat is pretty taught, it crushes the aspirin into powder.

  9. #9

    Re: Engine overheating but lower radiator hose is

    Park on an incline and jack the front of the car up. It makes bleeding the system way easy. I personally have filled up the cooling system in my S13 about 20 times doing various things and I've never once thought it was hard or spent more than 5 mins on it.

    My M3... now that's a completely different story. That thing takes at least 30 mins to get the air out since it doesn't have a radiator cap like Nissans do(it has an integrated expansion tank that is part of the cooling circuit and a small plastic bleed screw on a radiator endtank).


    Make sure to use the bleeder screw when pouring in coolant, it really pushes the air out when you jack the front up a bit.

  10. #10

    Re: Engine overheating but lower radiator hose is

    heh u know if all else fails that means ur radiator might be clogged... (experience from customer cars comming in for same reason top hot lower cold... good luck, hope its air and not anything else.

  11. #11

    Re: Engine overheating but lower radiator hose is cold

    Two things:

    1) use a Nissan OEM thermostat

    2) make sure the thermostat was not put in backwards

    On a long night, I ended up putting the thermo in backwards and had the same issues you described (over flow tank bubbling after a few mins, upper hose hot, lower hose cold, etc).

    good luck

  12. #12

    Re: Engine overheating but lower radiator hose is


    2) make sure the thermostat was not put in backwards

    thermo could also be upside down. make sure that bleeder valve thingy is facing up.

    lower hose is supposed to be cooler than the upper hose...that means the system is doing its job. is it actually cold or is it just warm compared to the upper hose?

    has it been driven long while overheating? i was running into the same issues as you and found it to be a warped head. got that milled down, put a new headgasket in, worked like a charm.

  13. #13

    Re: Engine overheating but lower radiator hose is

    The car has been driven while overheating. My sister was driving and didnt know what to do. It seemed to overheat but then go down pretty quick often.

    I took out the thermostat and tested it and its fine and right side up. The I made sure the radiator wasnt clogged.

    The car runs very well untill it overheats. No smoke during any point and starts up right away. But if you were to tell me the head was warped i wouldnt be shocked at all. Is there a way to test for this?

  14. #14

    Re: Engine overheating but lower radiator hose is

    The car has been driven while overheating. My sister was driving and didnt know what to do. It seemed to overheat but then go down pretty quick often.

    I took out the thermostat and tested it and its fine and right side up. The I made sure the radiator wasnt clogged.

    The car runs very well untill it overheats. No smoke during any point and starts up right away. But if you were to tell me the head was warped i wouldnt be shocked at all. Is there a way to test for this?
    Compression test or Leakdown test will both tell you. If it was warped, you'd probably be burning coolant and you said it doesn't smoke. Anyways, your cylinders should be within 20 psi of each other for compression.

    Just to make sure, you put the air hole that's on the thermostat at the top and you put the spring of the thermostat IN TOWARDS the thermostat housing/or engine, right?

  15. #15

    Re: Engine overheating but lower radiator hose is

    The car runs very well untill it overheats. No smoke during any point and starts up right away. But if you were to tell me the head was warped i wouldnt be shocked at all. Is there a way to test for this?
    sound identical to my problem. in fact, if you look far enough back, you'll see i started an identical topic and came up with plenty of theories of what it was.

    if the car was driven while overheated, a warped head is more than just a possibility. mine didnt smoke or have coolant on the oil. there is a way that shops can test it. someone else will have to fill you in on the details, but there is an additive that you put in the coolant that can detect leaks. i think it changes color if it does..im really not sure.

    if you do go ahead and get the head milled, make sure to attach the upper timing cover to the head before you take it in. that has to be the same level as the head. i learned that the hard way.

    good luck

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