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Thread: 328i Temp gauge won’t reach middle

  1. #1
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    328i Temp gauge won’t reach middle

    After swapping in another M52 from a 528i into my 328is (old motor blew), the temp gauge struggles to reach operating temp. Couple weeks ago, car threw a code for a bad engine coolant sensor and the code reader showed it idling at 140 Fahrenheit. Replaced it right away. Gauge still has same issue. Tried bleeding the coolant system more, no air seems to come out. Figured it could be a bad t-stat so I replaced it today, but temp gauge still stays below 1/2 mark unable to reach operating temp. After more bleeding and the heater still blowing solidly warm air (not piping hot or anything), issue still persists. Could there still be air in the cooling system? What other reason could it be?
    I’m afraid to drive it too far if the temp gauge could possibly be inaccurate, don’t want to blow another motor here boys. Any help is appreciated!

  2. #2
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    I once put in a new, but el-cheapo, tstat, (probably autozone) and continued to have problems. I finally put in a good one, and problems went away.

  3. #3
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    Quote Originally Posted by zellamay View Post
    I once put in a new, but el-cheapo, tstat, (probably autozone) and continued to have problems. I finally put in a good one, and problems went away.
    I replaced it with a Wahler 92C tstat, which is OEM. The old tstat I replaced was the exact same. When it comes to the cooling system I never go cheapo, I stick to OEM or better. I upgraded my entire cooling system, I have an aluminum Mishimoto radiator and expansion tank, all new hoses and clamps, Stewart metal water pump, aluminum thermostat housing.

  4. #4
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    Did you test the Tstat before install? Put it in boiling water? Installed with arrow point up?
    1997 Arctic Silver/Black M3
    CES Stage IV (651rwhp/615rwtq @ 24 psi)

    1999 Techno Violet/Dove M3
    Auto/Convertible and staying stock!

  5. #5
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    Quote Originally Posted by BMWManiac View Post
    Did you test the Tstat before install? Put it in boiling water? Installed with arrow point up?
    I didn’t test it but yes I installed it correctly, arrow pointing up. Also worth nothing that the old tstat was not stuck open or closed, seems to still be fine and probably reusable. I’d hope that a brand new oem thermostat works correctly but you never know I guess. Both upper and lower rad hoses get pretty warm after running for a while, upper being hotter obviously.

    This might be a dumb question but are the radiator hoses supposed to be squishy/squeezable after warming up? Or stiff? And what about when cold?
    Last edited by shadze36; 01-04-2020 at 09:35 PM.

  6. #6
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    At that temperature you will not build any pressure and the hose will be soft. If you get near 100 deg C, you will build lots of pressure until the pressure relief opens in the expansion tank cap at 30psi.

    - - - Updated - - -

    Is your fan clutch disengaging correctly? It could provide too much cooling.

    The only time I've experienced cold coolant issues was when the thermostat was bad in my e39 M5.

  7. #7
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    So it’s more likely that my temp gauge is accurate and my engine is just running cold and my coolant is not getting up to temp enough to even open the thermostat? I would be more worried if the gauge is just inaccurate for some reason. But still, a cold engine is bad.

    I’m not sure about the fan clutch, I haven’t given it a look because I’ve been more focused on the other parts. How do I tell if it’s disengaging correctly?

  8. #8
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    Quote Originally Posted by shadze36 View Post
    So it’s more likely that my temp gauge is accurate and my engine is just running cold and my coolant is not getting up to temp enough to even open the thermostat? I would be more worried if the gauge is just inaccurate for some reason. But still, a cold engine is bad.

    I’m not sure about the fan clutch, I haven’t given it a look because I’ve been more focused on the other parts. How do I tell if it’s disengaging correctly?
    Its not that your car isn't opening up the thermostat....it is that your car is running with an open thermostat. The coolant temp sensor for your gauge is plugged into the side of the block, under the intake manifold. Once your car gets up to a certain temperature, your thermostat should open, allowing coolant to flow throughout the cooling system to maintain the correct temp. So, typically when these engines don't get to operating temp, it has to be the thermostat. Maybe test the coolant temp sensor in the radiator next.
    Last edited by BMWManiac; 01-05-2020 at 07:40 AM.
    1997 Arctic Silver/Black M3
    CES Stage IV (651rwhp/615rwtq @ 24 psi)

    1999 Techno Violet/Dove M3
    Auto/Convertible and staying stock!

  9. #9
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    Quote Originally Posted by BMWManiac View Post
    Its not that your car isn't opening up the thermostat....it is that your car is running with an open thermostat. The coolant temp sensor for your gauge is plugged into the side of the block, under the intake manifold. Once your car gets up to a certain temperature, your thermostat should open, allowing coolant to flow throughout the cooling system to maintain the correct temp. So, typically when these engines don't get to operating temp, it has to be the thermostat. Maybe test the coolant temp sensor in the radiator next.
    Right. The fan clutch has nothing to do with it. If the tstat is working properly, none of the water being cooled in the radiator will enter the engine until it's up to running temperature.

  10. #10
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    Quote Originally Posted by shadze36 View Post
    After swapping in another M52 from a 528i into my 328is (old motor blew), the temp gauge struggles to reach operating temp. Couple weeks ago, car threw a code for a bad engine coolant sensor and the code reader showed it idling at 140 Fahrenheit. Replaced it right away. Gauge still has same issue. Tried bleeding the coolant system more, no air seems to come out. Figured it could be a bad t-stat so I replaced it today, but temp gauge still stays below 1/2 mark unable to reach operating temp. After more bleeding and the heater still blowing solidly warm air (not piping hot or anything), issue still persists. Could there still be air in the cooling system? What other reason could it be?
    I’m afraid to drive it too far if the temp gauge could possibly be inaccurate, don’t want to blow another motor here boys. Any help is appreciated!

    You are describing a tstat that is stuck open. Also, how long are you waiting for it to come up to temp? At idle, it can take a long time. Go for a spin around the block, a few miles -- less than 5 -- should do the trick.

    - - - Updated - - -

    Quote Originally Posted by zellamay View Post
    Right. The fan clutch has nothing to do with it. If the tstat is working properly, none of the water being cooled in the radiator will enter the engine until it's up to running temperature.

    Not to put too fine of a point on this, but the tstat cycles open and closed to hold the temp. If the engine is running cold, the tstat is stuck open, as you stated. Coolant in the engine heats and the tstat opens, the relatively cold coolant in the radiator and the hot coolant in the engine exchange places and the tstat closes again, the cycle repeats.

  11. #11
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    The fan clutch, if defective, will create a condition where the temperature will rise if the car is stopped -- heavy traffic, that sort of thing -- then come down again when the car speeds up again. As the car is moving, air is forced through the radiator to cool it, the fan essentially free wheels to save energy (gas). When the car stops moving, the fan clutch kicks into action to force the fan to spin and draw air through the radiator. The fan clutch -- also called a viscous couple -- has a jelly-like material inside that expands when it heats up, this expansion causes the fan to be coupled to the pulley that is driven by the serpentine belt. You can test for a bad fan clutch by CAREFULLY using a folded rag to rub on the edge of the fan to bring it to a stop as the engine idles. Then, spin the fan in the opposite direction that it wants to go, it should go the right direction soon after completing one revolution in the wrong direction. It it coasts in the wrong direction for several rotations, the couple is worn out.

    The fan clutch would give the opposite problem you are reporting, the car would heat above midpoint on the gauge at idle.

  12. #12
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    Quote Originally Posted by JDStrickland View Post
    You are describing a tstat that is stuck open. Also, how long are you waiting for it to come up to temp? At idle, it can take a long time. Go for a spin around the block, a few miles -- less than 5 -- should do the trick.
    After putting in the new tstat yesterday, during the bleed the car was on for about 10-12 minutes. It slowly crept up to a little past the 1/4 mark. Then I gave it a few revs, letting it hang around 2500rpm for a few seconds, with the bleed screw open. Temp gauge didn't budge. I shut the car off and I checked the rad hoses after, upper was pretty hot and the lower was cold. With the old tstat both hoses wouldve been warm at this point. This gave me the impression that the tstat didn't open yet.
    Last edited by shadze36; 01-05-2020 at 04:25 PM.

  13. #13
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    Quote Originally Posted by JDStrickland View Post
    The fan clutch would give the opposite problem you are reporting, the car would heat above midpoint on the gauge at idle.
    Thank you, this is what I assumed. In this case my fan clutch is not the problem then. Now I will just have anxiety for another cooling system component that could possibly blow up my motor if it fails

  14. #14
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    Quote Originally Posted by shadze36 View Post
    After putting in the new tstat yesterday, during the bleed the car was on for about 10-12 minutes. It slowly crept up to a little past the 1/4 mark. Then I gave it a few revs, letting it hang around 2500rpm for a few seconds, with the bleed screw open. Temp gauge didn't budge. I shut the car off and I checked the rad hoses after, upper was pretty hot and the lower was cold. With the old tstat both hoses wouldve been warm at this point. This gave me the impression that the tstat didn't open yet.

    Go for a drive, a couple of laps around the block so you don't have to walk too far if it does not go well, and it should heat up fine. Your test is flawed, mostly due to not enough time. I live 1.5 miles from the freeway, it takes all of it to warm up to midscale.

  15. #15
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    UPDATE -

    Listened to JDStrickland and he was absolutely right. After a couple miles of driving around, the temperature gauge finally hit dead center and actually stayed there! The heater also felt hot as well, during driving and idle, probably due to my obsessive bleeding beforehand. I will continue to monitor the coolant level. It's safe to say that the old thermostat was the culprit. I feel pretty stupid now, but given my past experience with overheating issues, I was just trying to play it as safe as possible and not risk anything. Also shoutout to zellamay, BMWManiac and pizzaman for the input and helpful comments

  16. #16
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    Quote Originally Posted by shadze36 View Post
    UPDATE -

    Listened to JDStrickland and he was absolutely right. After a couple miles of driving around, the temperature gauge finally hit dead center and actually stayed there! The heater also felt hot as well, during driving and idle, probably due to my obsessive bleeding beforehand. I will continue to monitor the coolant level. It's safe to say that the old thermostat was the culprit. I feel pretty stupid now, but given my past experience with overheating issues, I was just trying to play it as safe as possible and not risk anything. Also shoutout to zellamay, BMWManiac and pizzaman for the input and helpful comments

    I have let my car idle for 20 minutes and not get up to temp. Undertemp is never a fatal condition, so you can drive a car with a cold engine. Overtemp is always a problem. After doing service, I take my car for a mile or two, it will either hit midscale and stop, or if it keeps climbing, I can get home before it becomes a fatal condition.

  17. #17
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    Quote Originally Posted by JDStrickland View Post
    Go for a drive, a couple of laps around the block so you don't have to walk too far if it does not go well, and it should heat up fine. Your test is flawed, mostly due to not enough time. I live 1.5 miles from the freeway, it takes all of it to warm up to midscale.
    I'm having the same issue. Replaced the fan clutch and now have the issue. I'll take the car for a drive and see what happens.

  18. #18
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    took it for a drive. Started out right at the edge of the cold mark. Drove about a mile and it started to get get off the edge of cold. Wouldn't get any higher that 1/2 way between the cold mark and the next mark for the next 7 miles. I decided to drive it hard. Kept the RPM's above 4k for the next 5 miles and it finally got to half on the gauge. As soon as I started driving more like normal the gauge went back down to half way between cod & the next line. I'm assuming thermostat.

  19. #19
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    I have tried "burping" the system for a few days and driving it after. Still can't get it to come up and stay up.

  20. #20
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    Anybody have a clue?

  21. #21
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    Looks like your thermostat is broken and always in full open position. Was the same on my M3 some years ago when the t-stat broke. Replaced t-stat and all was fine.
    Shogun tricks and tips for the E32 series are HERE!

  22. #22
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    I'll give it a go and let you know. I hope that's all it is.

  23. #23
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    Quote Originally Posted by B328iC View Post
    took it for a drive. Started out right at the edge of the cold mark. Drove about a mile and it started to get get off the edge of cold. Wouldn't get any higher that 1/2 way between the cold mark and the next mark for the next 7 miles. I decided to drive it hard. Kept the RPM's above 4k for the next 5 miles and it finally got to half on the gauge. As soon as I started driving more like normal the gauge went back down to half way between cod & the next line. I'm assuming thermostat.

    T-stat.

    I was doing 70+ on the freeway one day, and the temp gauge actually fell from midscale to the blue mark. The t-stat was stuck open. Given the options of sticking open or sticking closed, I'll take open any day of the week.

  24. #24
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    Pulled that out today. Doesn't look stuck open. I'm going to check it in a pot of water tomorrow to verify if it works or not.
    This is a total mind bender for me. Doesn't make sense. What temp should it start to open?

  25. #25
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    as per realoem installed is thermostat 92 CEL 11537511083 for a 328i.
    Shogun tricks and tips for the E32 series are HERE!

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