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Thread: Overheating issue

  1. #1
    Join Date
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    1990 325i BMW

    Overheating issue

    I have a 1990 325i its been parked for a few month while I took the head out and replaced a bunch of gaskets. I also replaced the timing belt, waterpump, thermostat, the two sensors on the thermostat. I had some starting issues a few weeks ago but I think those have resolved by just running the car.
    Now the engine sounds great, better than it has in the last 2 years. On cold start the rpms are a little erratic, but this has been ongoing for years, once the engine warms up the rpms settle. The issue is it overheats real fast.
    I checked the new water pump by disconnecting the exit hose and watching the water pump out. I had a faulty thermostat but it's been replaced, and even without the thermostat the car still overheats. I disconnected the radiator hoses and ran water through the top and it came straight out through the bottom.
    Some known issues are: my distributor-cap cover is loose (I think the female-thread came out for one of the bolts holding it in), The sensor on the passenger side of radiator could have the wires on wrong leads, I think its right via a old picture of mine but my plastic piece broke and i'm holding it together with electrical tape and connectors. My coolant bleeder valve is stuck shut, I have tried loosing it while my car was overheating to get it hot but to no avail.
    Thanks! any ideas on what to check next are appreciated. Im kind of lost here.

    edit:I have noticed the lower radiator hose is still cold while the engine is overheating.
    Last edited by donfly; 06-13-2024 at 12:38 AM.

  2. #2
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    you checked the temp with a gun? not just going by the gauge? the gauge can easily read high while the engine is not actually that hot.

    you need to get the bleeder bolt to come loose so you can bleed the air out but you should also be able to loosen the hose and bleed it too.

    how long does it take to get hot? it gets hot idling, running, or both?

    and you said you checked the water pump by disconnecting the outlet hose and watching the water come out? so you are sure the water pump is the correct direction pump? how old is your radiator? they stop working over time and you know how hot it gets here in our parts of texas. at least i have the breeze off the gulf here in corpus where you don't really have any cooling breezes up there, if i remember right from the snake farm and outlet malls

    - - - Updated - - -

    your electric fan comes on when the gauge gets to a certain point? and if you hit hte ac button, it comes on immediately? and your fan clutch is still good?
    woohoo!! finally found an early 318 again.
    september of 1983 build date.
    5 speed, roller windows, and non-pop out rear windows. also, so old that it has no overhead check panel, its on the dash.

  3. #3
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    goood chance it's an airlock ... get the bleed screw working and bleed out the system properly.

    if that doesn't do it there's an entire rabbit hole of issues it could relate to. bad fan clutch, warped head, cracked block or head, all sorts of stuff.

  4. #4
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    Quote Originally Posted by superj View Post
    you checked the temp with a gun? not just going by the gauge? the gauge can easily read high while the engine is not actually that hot.

    you need to get the bleeder bolt to come loose so you can bleed the air out but you should also be able to loosen the hose and bleed it too.

    how long does it take to get hot? it gets hot idling, running, or both?

    and you said you checked the water pump by disconnecting the outlet hose and watching the water come out? so you are sure the water pump is the correct direction pump? how old is your radiator? they stop working over time and you know how hot it gets here in our parts of texas. at least i have the breeze off the gulf here in corpus where you don't really have any cooling breezes up there, if i remember right from the snake farm and outlet malls

    - - - Updated - - -

    your electric fan comes on when the gauge gets to a certain point? and if you hit the ac button, it comes on immediately? and your fan clutch is still good?
    Ya thats my part of texas, my radiator is only about 2 years old, the water pump is orientated correctly if thats what you mean and i don't think theres much of a way to put the hoses in the wrong place otherwise.
    just tested the fan clutch and it is working
    I don't have a temp gun but the water I put in is boiling out when I leave cap off and run car. it takes about 8-10 mins to start overheating like that when idle, given I do rev the engine up a bit when idling.
    I have drove it around and I would say it takes about the same amount of time when driving.
    Thanks I will mess with the bleeder bolt some more tomorrow and if not just try to loosen hose. Maybe I can just bring the thermostat housing somewhere and get them to drill it out.

  5. #5
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    keep us updated
    woohoo!! finally found an early 318 again.
    september of 1983 build date.
    5 speed, roller windows, and non-pop out rear windows. also, so old that it has no overhead check panel, its on the dash.

  6. #6
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    Okay, took me a while to post. I've narrowed some things down. I went ahead and replaced the water pump again just in case. It was still overheating. I checked the compression and all 6 cylinders held good compression.

    For some reason, sill unknown the water is not circulating through the radiator even though I bleed the air, make sure radiator has good flow, make sure pump is pumping water through engine, and have the thermostat out.

    Again the car sounds great, it runs at a steady idle now, until it gets to normal operating temperature then the idle goes up about 1000 rpms. This is also the time when the temperature gauge has a steady rise until it reaches red. And the water starts steaming out of coolant tank if I leave it open.

    The oil has no cloudy appearance.
    In an attempt to force water through my radiator I plugged the hose from thermostat to radiator and thermostat to water pump. And connected it so that water goes from engine>radiator>water pump>engine. Doing this it seemed like it was working and water was moving through radiator but after about 20-25 mins the engine got to red and water began steaming again.

    I checked the compression again while car was hot and it was still holding compression. I assume the I will have to take the head out and probably resurface it. Not sure what else to do at this point or even if that's the real issue.

  7. #7
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
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    I don't know what all you've covered, but here's a good bleed procedure:
    https://www.bimmerforums.com/forum/s...6#post28749366

    Also, when you installed the thermostat did you ensure the pinhole was at the top?
    "Howdy, Folks!"

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  8. #8
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    To bleed air I just poured water directly into thermostat, and into the radiator separately. Until no more bubbles of air came out. I should try to jack up the front of car. I also have the bleeder screw unstuck now, but my cousin plugged the heater a few years ago not sure exactly why but I don't think it works, will this method still work?
    And I still haven't put my thermostat back, because I wanted to rule it out.

  9. #9
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    since the bleeder screw is unstuck, you can have the cap off the reservoir and the bleeder open. start the car and put coolant in the reservoir as you watch the bleeder. when you are getting a steady stream at the bleeder, no more air bubbles, than you can lock the bleeder down and put the cap on the reservoir and it should be good.

    my two boys and i are traveling through your area saturday. we are going to pick up another e30 from fort hood. another coupe with the engine in the trunk because they overheated it. definitely a surprise trip since the car just showed up on facebook out of nowhere for 1300 and looks great.
    woohoo!! finally found an early 318 again.
    september of 1983 build date.
    5 speed, roller windows, and non-pop out rear windows. also, so old that it has no overhead check panel, its on the dash.

  10. #10
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    Hope your having a safe trip. I went ahead took the head out again, took it down to Houston to get it resurfaced. Maybe this will work will keep updated.

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