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Thread: Car overheats

  1. #1
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    Car overheats

    I wont lie I only have just water in the coolant system right now I know that's retarded I understand that. Inky have it in there cause I found multiple leaks from thermostat housing and water pump and havent out coolant in it. Heres the story. Its 8o degrees out in great old ct. I drive to the parts store and I'm watching the thermostat go almost read I start driving it goes down. Only stays at optimal temp when I'm going 50 or above. My question is I found 2 wires that connect for what I'm guessing is the heatercore. Could that cause my car to overheat

  2. #2
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    Sounds like the thermostat has failed in open position. Additionally, something is amiss with your water pump and thermostat housing/housing seal.
    I would recommend replacing the thermostat, thermostat housing, water pump and related seals. Then go from there with further repairs.

    As for the loose wires, as I cannot see them, you are going to have to track that down.


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  3. #3
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    Quote Originally Posted by usarmy188 View Post
    I wont lie I only have just water in the coolant system right now I know that's retarded I understand that. Inky have it in there cause I found multiple leaks from thermostat housing and water pump and havent out coolant in it. Heres the story. Its 8o degrees out in great old ct. I drive to the parts store and I'm watching the thermostat go almost read I start driving it goes down. Only stays at optimal temp when I'm going 50 or above. My question is I found 2 wires that connect for what I'm guessing is the heatercore. Could that cause my car to overheat
    If its overheating while stopped or moving slowly and cools back down at speed, I usually suspect the fan clutch first. You also mentioned that there are leaks in the system, you need to address those soon and refill and bleed the system. From the sound of it without knowing more details, it sounds like you need a full cooling system overhaul regardless.

    Where are these unplugged wires located?

  4. #4
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    Quote Originally Posted by ChuckDizzle View Post
    If its overheating while stopped or moving slowly and cools back down at speed, I usually suspect the fan clutch first. You also mentioned that there are leaks in the system, you need to address those soon and refill and bleed the system. From the sound of it without knowing more details, it sounds like you need a full cooling system overhaul regardless.

    Where are these unplugged wires located?
    I've replaced water pump thermostat coolant hoses radiator mass airflow sensor headgasket all the other gaskets. Throttle sensor camshaft sensor 02 sensors. I dont understand

  5. #5
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    Since you overheated your going to have to check that the head is not damaged, you have to do a compression test. If you let the temp get anywhere near the red then the head can crack and warp.
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  6. #6
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    Quote Originally Posted by ChuckDizzle View Post
    If its overheating while stopped or moving slowly and cools back down at speed, I usually suspect the fan clutch first. You also mentioned that there are leaks in the system, you need to address those soon and refill and bleed the system. From the sound of it without knowing more details, it sounds like you need a full cooling system overhaul regardless.

    Where are these unplugged wires located?
    I've fixed the system and bleed it already.

  7. #7
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    Quote Originally Posted by usarmy188 View Post
    I've fixed the system and bleed it already.
    You mentioned that you had done the headgasket recently. Was the cylinder head checked at a machine shop for cracks or warping. Like Eric93se said, the heads can warp and crack when overheating. If you simply replace the gasket without machining the head it will eventually fail again. I made that mistake with my e30 the first time I did the head gasket and took the risk by skipping the machine shop process as I wanted to do the job quickly and for less money.

  8. #8
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    No I never sent it out to a shop. And when it overheated it wasnt even bad. The car didnt even force itself off. The headgasket was original and messed up anyways. I checked with 3 of my friends that were mechanics they said it was fine and sent it out.

    - - - Updated - - -

    My question is can it be overheating due to the fact I dont have the heater core electrically hooked up.

  9. #9
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    Quote Originally Posted by usarmy188 View Post
    No I never sent it out to a shop. And when it overheated it wasnt even bad. The car didnt even force itself off. The headgasket was original and messed up anyways. I checked with 3 of my friends that were mechanics they said it was fine and sent it out.

    - - - Updated - - -

    My question is can it be overheating due to the fact I dont have the heater core electrically hooked up.
    Answer to your question: No, can't be related to this.. Whether the heater core (cabin heater) valves are open or shut, this should not influence the cooling. Yes, opening the valves and running the cabin fan at full speed will help cool down the coolant, but this is only for emergencies when the cooling system isn't working okay.

    The first you want to check is your viscous clutch fan. If the clutch doesn't engage fully when the radiator is hot, you won't get enough airflow through the radiator when standing still. That will cause your engine to overheat.

    A very easy and cheap fix for now (if the problem is ONLY the viscous clutch fan) is to install the lower temperature 'temperature switch' in the radiator. Should cost only 20-30 dollar and you can install it in 5 minutes. Next, the aux fan will turn on when the coolant on the cool side of the radiator rises above 80 degrees C. And it will turn on the high speed fan at 88 degrees C. Should help a lot and will prevent the engine from overheating in most cases (if indeed the ONLY problem is the viscous clutch fan).. You have a 98 328i, so you'll need the modern type temperature switch with small pins. Part number can be found in the numerous fan delete mod threads on this forum.

    The fact that the coolant temp remains okay while driving means the rest of the cooling system is working more or less, and only fails when there is not enough air flow through the radiator.

    P.S. You'll have to replace water pump probably and thermostat gaskets.. But those leaks don't mean the pump isn't functioning properly. Leaks will need to be fixed though, because you'll probably also get air in the system, and you risk running low on coolant if the leaks get worse or on long trips.

    P.P.S. "The car didnt even force itself off." is no guarantee at all. It will have to overheat extremely for the pistons to seize in the cylinders.. If the temp gauge gets anywhere the red zone, you're in risk of cracking your head and headgasket.. The temp gauge was badly designed by the BMW engineers and the red zone should have been positioned at a lot lower temperature, and every BMW should have had an alarm once the temperature rises above say 110 degrees C.
    Last edited by ed323i; 07-21-2018 at 01:05 PM.


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  10. #10
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    I think your car might be overheating because it is only water in there. Water can only reach a certain temperature (boiling point) before it turns into steam. Steam carries more thermal energy than water and it gets much hotter as a result. If you mix in some actual coolant to raise the boiling point I think you will stop overheating

  11. #11
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    Actually the system is pressurized so the boiling point of water is raised, also the system under normal operation is just below the boiling point of water (unpressurized). Boiling point of water at the 30psi rated stock cap is 250F.

    The OP probably warped the head from overheating it.
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  12. #12
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    Getting slightly off-topic here, but I think you'll find this interesting:
    Decided to look up all the parameters/dynamics of the water-coolant mixture, and found this very interesting article: https://hellafunctional.com/?p=629 (also has some great charts).
    Interestingly pure water has a lot higher heat capacity compared to pure ethylene glycol.
    Here is a quote: "The heat capacity is basically how much heat energy the coolant can carry out of the engine and to the radiator. As far as carrying heat goes, water does a really good job. It’s actually one of the most effective coolants that could possibly be used. The specific heat capacity of ethylene glycol is only about 65% of water at the temperatures seen in a cooling system. That means that to cool the engine by one degree, you would need about 50% more of it than straight water. So even though you could use pure antifreeze as a coolant, or any other liquid for that matter, you would need a bigger radiator and more robust cooling system compared to one that used straight water."

    So, if there is no risk of freezing, you don't mind the added corrosion with pure 100% water coolant (which can be fixed by using additives), and you assume your cooling system is always pressurized once the engine reaches operating temperature (which it won't if you have a more than small leak in your system), then pure water is the best you can choose.

    His conclusion:
    "So, in conclusion, you should only use as much anti-freeze as is necessary for your climate and operating conditions, and those coolant “wetting” additives are generally a good thing to use."

    I'm gonna refill the coolant soon and I'll use even less of the BMW coolant and add more distilled water this time.
    Last edited by ed323i; 07-21-2018 at 08:01 PM.


    1997 E36 BMW 323i
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  13. #13
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    Quote Originally Posted by XnWarden View Post
    I think your car might be overheating because it is only water in there. Water can only reach a certain temperature (boiling point) before it turns into steam. Steam carries more thermal energy than water and it gets much hotter as a result. If you mix in some actual coolant to raise the boiling point I think you will stop overheating
    Lots of people run with distilled water only, especially for track use. For the track, I prefer distilled water and then I add some Redline Water Wetter (highly recommended and approved pretty much by every race organization). Many motorsports organizations have rules where you do not add coolant to the cooling system. I don't think OP's overheating is an issue with the water in the system.

  14. #14
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    Quote Originally Posted by ChuckDizzle View Post
    Lots of people run with distilled water only, especially for track use. For the track, I prefer distilled water and then I add some Redline Water Wetter (highly recommended and approved pretty much by every race organization). Many motorsports organizations have rules where you do not add coolant to the cooling system. I don't think OP's overheating is an issue with the water in the system.
    Thanks for the info. Learn something new every day

  15. #15
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    I don't think the water is the issue. However considering you have leaks on the WP and t-stat you just did, and also didn't get the head checked when doing the HG, you could have a litany of problems and I hate to say can't rule out any potential causes because you just did the work.

    Based on your symptoms I'd initially lean towards an issue with the fan clutch though.

    Sent from the dark side of the Moon

  16. #16
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    Besides providing antifreeze and boiling point benefits coolant also acts to lubricate the pump, resist corrosion and maintain pH. Distilled water is fine in moderate climates but you need to flush it far more frequently than coolant.

    But anyway, do what ed3231 said in his first post.
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  17. #17
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    Quote Originally Posted by XnWarden View Post
    I think your car might be overheating because it is only water in there. Water can only reach a certain temperature (boiling point) before it turns into steam. Steam carries more thermal energy than water and it gets much hotter as a result. If you mix in some actual coolant to raise the boiling point I think you will stop overheating
    It wont turn to steam at 100°C because it's under pressure ergo higher boiling point.

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  18. #18
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    If you let it get hot you likely have damaged the head. They can crack between the exhaust valve seat and the cooling port. It is not easy to see unless you know exactly where to look. The temp gauge is not linear and by the time it is moved past center you have problems. The red zone means your head is likely damaged. Also the surface finish of the head is critical for a long lasting head gasket seal. Several engine shops I have talked to will do a very slight skim on every head even if it is perfectly straight just to make sure the surface finish is optimal.

    You need to fix the obvious problem which is that your mechanical fan isn't working. Or the water pump isn't flowing as much as it should. I have heard of water pumps with the impeller backwards so a visual comparison to the old one would be helpful. If you overheat while moving slow but cools down when moving fast then air flow through the radiator is not adequate at low road speed or water flow through the engine/radiator is not adequate at low engine RPM. A centrifugal pump like our water pumps will flow some if spinning the wrong direction but not as much.

    Do you get a misfire or rough running for a few seconds after a cold start? That is a good indicator of water being in a cylinder, pushed there by the cooling system pressure after the engine is shut off.

    A hydrocarbon test of the coolant/water would also check for exhaust gasses in the cooling system, pushed there by higher pressure in the combustion chamber than the cooling system while the engine is running.

    A leak down test, not just a quick compression test will tell you if there is a slight leak.


    Just as a comparison though I have a stock radiator, Stewart water pump, 88C Wahler thermostat no mechanical fan, and 80/88C aux fan switch. I have an Autometer water temp gauge with the sending unit in the stock cylinder head location. I see 200F rock solid even when moving slowly like 15 mph, the fan only runs when I have been stopped for a decent amount of time in hot weather. Like at least a couple minutes. The temp gauge NEVER goes above 210F even with continued idling. The fan will bring the temp down and turn off for a while just like any other car.

    What I am getting at is that you should not need to be going 50 mph to keep it cool even with a totally broken or removed mechanical fan. Which is why I suspect a problem with the pump or possibly the thermostat itself isn't opening adequately and only the higher revs while driving faster increase the flow enough keep it cool.
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