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Thread: Engine not heating

  1. #1
    Registered User BillD's Avatar
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    Question Engine not heating

    During the summer Atlanta heat, my 240z ran beautifully, never going over about 180F. Now that the temperatures have gotten a little cooler, (40-50F), it is taking close to 10-20 miles to show any movement at all on the temperature gauge. Even then it stays very low. I've taken readings from the radiator with a non-contact thermometer and they read less than 120F when the needle hasn't moved. It still runs beautifully other than than those readings. (Of course, the heater blows cold air during this time!)

    Am I correct in assuming that the thermostat is either faulty or removed. I plan on changing it. I've done this on other cars, but is there anything I should look out for on the 240z. (It has a 2.8L engine transplanted.)

    Thanks in advance.
    1973 240z L28 engine
    1985 300zx
    1959 AH 100-6 289 v8
    1947 Ford 2N/8N hybrid (SN 8N0268)
    Kawi ZX11, Ural
    GaZClub #676

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    Default Re: Engine not heating

    Originally posted by BillD
    ...............Am I correct in assuming that the thermostat is either faulty or removed. I plan on changing it. I've done this on other cars, but is there anything I should look out for on the 240z. (It has a 2.8L engine transplanted.)

    Thanks in advance.

    I would say that there is a good chance the thermostat has become stuck in the open position (or was removed for some reason); I'd do as you mentioned, and replace it (or add it back). It's quick and easy, and good preventative maintainance.

    When you start the engine from dead cold, with the radiator cap off, can you see the water in the radiator top tank "flowing" from the water pump? If so, that would confirm the thermostat either stuck open or missing. There should be no "flow" until the water in the engine gets hot enough to trigger the thermostat opening (usually a 180 degree thermo, though some run a 160 degree).

    BTW, I just came back from a drive in my Z. Temp is about 55 degrees, and it took 5 minutes at high idle w/ choke on for the thermostat to open. Before it opened, the water in the radiator was cold to the touch and the surface of the water was "still", when the thermo opened, the water got too hot to touch immediately and "flow" was obvious.

  3. #3
    HLS30165540
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    Don't forget to replace the gasket and take advantage of this opportunity to flush and replace the coolant.
    The 1973 240Z 165540 Slightly modified. L28, 5sp, cam, headers, MSD 6AL, power windows, power door locks, leather seats, custom this and custom that.

  4. #4
    Registered User BillD's Avatar
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    Default

    Thanks for the advice. Any recommendations for gasket sealant?
    1973 240z L28 engine
    1985 300zx
    1959 AH 100-6 289 v8
    1947 Ford 2N/8N hybrid (SN 8N0268)
    Kawi ZX11, Ural
    GaZClub #676

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    Sounds like you're on the right path.The biggest gotcha is bolts on the thermo housing snap !!Especially the one closest to the block.I would suggest first very gently tighten that bolt just a fraction.Then loosen a little.Continue this tighten a little,loosen a little. What that does is lets the threads cut and clear themselves.The tightning clears the build up on the threads that accumulates from continualy going in one direction.Apply teflon tape or such for easy future removal. DON"T FORCE IT OR YOU"LL SNAP IT!! Take your time. Oh yeah its common to get air in the system that causes the car to get hot when you think there is enough coolant. Carry some with you .
    Last edited by Daniel; 11-17-2003 at 05:33 AM.

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    Default

    Originally posted by BillD
    Thanks for the advice. Any recommendations for gasket sealant?
    With clean surfaces, none should be necessary. If you "must" use something, I would use common silicone sealant in this location, but it should not be necessary to use any sealant.

  7. #7
    Registered User BillD's Avatar
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    Smile Success

    I finished my 240z thermostat project this afternoon. Everything now works fine. After about three miles, the needle passes 120F and after about five miles it has reached the center of the dial (about 190) and stays there. Before, it was still not past the 120F point after about 20 miles on a cool day. The strange thing is that the old thermostat looks like it was shut and when I tested it in a pot of hot water, it opened at 180F just like it was supposed to. So I fixed the problem, but I'm not sure why it was a problem. Maybe the old thermostat was stuck open and I scared it shut when I took it out.

    I didn't use any sort of gasket sealer and I can find no leaks, so that looks good. The only strange part about the gasket was that the replacement gasket had two holes (like the picture in the Chilton Manual) but the actual gasket and thermostat housing had three bolts. I was able to modify the gasket to fit, but I'll have to remember this in the future.

    Thanks for the help and advice.
    1973 240z L28 engine
    1985 300zx
    1959 AH 100-6 289 v8
    1947 Ford 2N/8N hybrid (SN 8N0268)
    Kawi ZX11, Ural
    GaZClub #676

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    Default

    Later Z's (I do not know when the change occured) had the Thermo Housing with three bolts needed to hold the cover to the housing. Sounds like they gave you a gasket for a 240 and your L28 was out of a car that had the other (3 bolt) Thermo housing.

    I've had the same situation with the Thermostat looking OK and operating OK in a pot of water, but it had obviously not worked earlier when installed in the engine, Never did figure out why, but now days I routinely change the Thermostat at the first sign of any unusual heating or lack of heating of the engine. I try to have a couple of new ones, and gaskets in my parts stores.

  9. #9
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    Yes the deinstall may have seemed to fixed the old thermo. but, hot water test under no pressure is not absolute. The thermo opens and closes alot during normal operation.It doesn't just open and thats it until the car is cold again.Its job is to maintain a constant temp. The absolute test is to replace it. You did and it is now absolutley fixed. Absolute good job!!

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