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Thread: High water temp. Can’t figure this out.

  1. #1
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    High water temp. Can’t figure this out.

    So I have been chasing lower water temperatures for a while now and I can’t seem to figure this out. On my 95 M3 I am running the following:

    Stock clutch and fan
    Stock auxiliary fan (verified that both low and high speeds work)
    Stock water pump
    Stock fan switch
    Stock 88 degree thermostat
    “Upgraded” to the s54 z3 m radiator


    All of the above have been replaced and have less than 30,000 miles. My water temps are being measured with one of those adapters that go in between the hot side of the thermostat housing to the radiator inlet. Prior to my stock radiator inlet pipe cracking at the track, I was running the stock radiator and I feel like my temps were easily under 220 degrees Fahrenheit and under normal traffic conditions rarely over 200.

    After switching radiators to the supposedly more efficient/better z3 m radiator I noticed higher temps. I have bled and bled and bled and can’t figure it out. Temps seem to be running around 200-210 under normal driving conditions. The track I’m hitting 220 after a few laps and have to constantly back off. I have built some new radiator shrouding since the z3 radiator is a few rows shorter and not getting as much airflow and that seemed to help as I see a pretty quick drop in temp after I start moving. I did a coolant flush (engine block as well since I haven’t tried that yet) the other day and bled with a vacuum bleeder and also bled again the “usual” way.

    Drove last night (70 maybe 80 outside) and temps seemed nice. Below 200 and would drop down to 194 at times. Usually sat around 196 then would go to 199 and the thermostat would open and drop back down to 196. Seemed great.

    Topped off the coolant this morning and drove to work (all highway going 3200 rpm maybe in 5th) and was hitting 207 degrees it’s a warm day (90s) but still seems terribly high based on other threads I’ve seen with people running similar setups and measured at the thermostat housing.

    I’ve got a track day coming up and I’m worried I will be seeing super high temps again. I try to back off before reaching 220 but idk if I could really push it any higher.

    I’m starting to consider upgrading water pumps or maybe even going with a new radiator at this point. Would the lower temp fan switch help or is this more of a fix for temp at idle? I’d really prefer trying to get the stock system working properly but I’m out of ideas and out of coolant.
    Last edited by ewrjontan; 09-20-2022 at 11:44 PM.

  2. #2
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    My thermostat was stuck open and I was getting way hotter than I should have - kind of what you describe. This was happening both on track and just driving.

    The car would run as low as 185 even in 100+ ambient weather while sitting in traffic, but would get up to 215 in sustained highway driving, and got super hot on track - I was constantly having to back off.

    I'm still figuring things out, but I DID replace my thermostat. I think it was both not closing and also not fully opening, either. I also did the Z3M radiator, as well as all new ducting including the aluminum bottom duct.

    I did a track day this weekend and by the end of the day ambient temps were reading just over 100 in the car. I was running happily cool but getting warmer as the day heated up. I got up to 223 at the end of my last session, which I think was a pretty good indication that things were being kept under control.

    Did you replace your thermostat?

  3. #3
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    The thermostat is most likely the culprit. Whenever I replace a thermostat I always test it before installing it. Even new thermostats can be faulty. All it takes is a pan of water on the stove and a thermometer.

    It eliminates having to replace the thermostat twice.

  4. #4
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    Interesting. I guess I should add that all of the components have been replaced and have less than 30,000 miles. Obviously things can fail before that though.

    The thermostat definitely seemed to be working as my radiator inlet hose did not start to get warm until higher temps (when I was bleeding) but I guess if it’s not opening fully that could be an issue. Is just hate to replace parts that are working properly.

    Any reason NOT to go with a low temp thermostat? I don’t drive in winter anymore so not getting up to temp won’t be an issue. But I also don’t know if it would make any difference on the track.

  5. #5
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    A few thoughts: look at ONLY the things you changed when the problem started, not everything. I once had a new tstat fail to work properly. ....... You say the Z3 radiator is "a few rows shorter", so it is probably the S54 radiator, meant to be run with an oil cooler. Either way, an oil cooler helps. I installed an oil-cap oil cooler on my Z3M S52, and I think it helped. Water temp never goes above thermostat opening temp (TDC on gage). Oil temp ranges from 205-215 max during phoenix summer under any conditions. ....... What do you mean " topped off the coolant this morning" ? Where did it go? If it's not leaking out, or going out the exhaust pipe, then the coolant was low before (not bled properly).

  6. #6
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    Correct. I guess I figured everyone saying it was more efficient compared to the stock e36 radiator that I didnt necessarily consider that it may be more efficient WHEN PAIRED with the oil cooler.

    I bled the system last night. Went for a drive and what not. The level dropped this morning after it cooled down so I topped off to the appropriate level of coolant.

  7. #7
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    Well, something is wrong if you have to "top off" the coolant after one drive. It's either leaking (first place to look is water pump or tstat housing or hoses: the things you messed with recently), going out the exhaust pipe (shouldn't be this because you have not said the car overheated), or not bled correctly (not to insult of course). I would figure this out before replacing/buying any parts.

  8. #8
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    Interesting. I thought that was completely normal? I have always had to do this after a bleed. No leaks whatsoever. I fill the coolant all the way to the top of the reservoir and constantly refill as it slowly flows out of the bleeder with the air bubbles along with it. I usually bleed with the motor on so at this point car is up to temp and fluid is hot. Once it cools down the fluid level drops down and my reservoir was a little low. Literally every write up mentions this step after every bleed so I don’t think that this is weird especially with no signs of leaking.

    But here I am with temp issues so fuck me right? Haha.

    Edit: so I went ahead and tested my auxiliary fan to make sure both low and high speeds are working by jumping the switch harness. Both settings work fine. I have certainly seen the fan turn on and off as well so it seems to be working fine.
    Last edited by ewrjontan; 09-20-2022 at 11:47 PM.

  9. #9
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    Here's a thread on bleeding, read post #2. ..... https://www.bimmerforums.com/forum/s...question-(S52) ..... You say "mentions this step after every bleed", which may be right, but not "bleed or top-off after every time you drive the car". Something is wrong. I drive my S52 Z3M all summer in Phoenix, and "top-off" about 1 cup a year.

  10. #10
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    Brother I’m not bleeding the car every time I drive it. I literally just flushed the radiator and block the other day and then bled it. I then topped it off to the appropriate level after it cooled down in the morning.

  11. #11
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    Quote Originally Posted by ewrjontan View Post
    Brother I’m not bleeding the car every time I drive it. I literally just flushed the radiator and block the other day and then bled it. I then topped it off to the appropriate level after it cooled down in the morning.
    Sorry, I misunderstood. This is good: no coolant loss to chase.

    I think the S54 radiator is 3 row and shorter than the S52 which is 2 row, so about the same capacity. Neither one would be a "downgrade", so that should not be the problem. Tstat?... several comments above Yes, if it is not opening fully, it could act normally until the engine is run hard. That's what my brand-new-bad tstat did. Fan clutch?... you didn't change it, so not really suspect, but still should be checked.

  12. #12
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    Fan and clutch were replaced. Everything in the coolant system in terms of main components (so everything other than any of the little hoses near the manifold) has been replaced with Genuine BMW parts. The S54 radiator is shorter and possibly a tad bit thicker.

    I am considering the thermostat which is a real bummer. I might go ahead and grab a high flow water pump while I am in there as well. Any reason to grab a low temp fan switch or low temp thermostat or just call it a day with an oem 88 degree thermostat?

  13. #13
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    Quote Originally Posted by ewrjontan View Post
    Brother I’m not bleeding the car every time I drive it. I literally just flushed the radiator and block the other day and then bled it. I then topped it off to the appropriate level after it cooled down in the morning.
    I think he misunderstood. You're correct about topping off after a major replacement / bleed.

    I'd also suggest that might be part of the problem you're having - there might still be air pockets.

    I swapped to the Z3M radiator and it IS more efficient - full stop. I haven't installed the oil cooler yet and I'm still running cooler than I ever have.

    So yes, your temps are higher than I'd expect. There must either be some air in your system still or something else is weird, like a bad thermostat. As I mentioned before, they can fail to open fully which can cause your symptoms. How hot does it get just sitting there idling? If it stays cool, that works also suggest it's not opening fully.

    I can't think of a reason a low temp thermostat would be problematic, especially given your location.

  14. #14
    NeilM is offline Member BMW E36 M3 Expert
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    Quote Originally Posted by blckstrm View Post
    I can't think of a reason a low temp thermostat would be problematic, especially given your location.
    Because under low cooling demand conditions a low temp t'stat will make the car run cooler than designed. Under high cooling demand conditions it won't help at all because the t'stat setting doesn't affect the total cooling capacity of the system (except in a negative way*) — it just initiates the same cooling ability a bit earlier.

    Also, if the OP has emissions testing where he is, an abnormally cool running car will almost certainly fail.

    * Other things being equal, a higher temperature differential between the cooling air and the coolant temperature increases the rate of heat energy transfer. Therefore an unusually low coolant temperature will reduce the system's cooling capacity.

    I agree the OP should drop in a new (standard calibration) t'stat and see what happens.

    Neil

  15. #15
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    Quote Originally Posted by ewrjontan View Post
    Fan and clutch were replaced. Everything in the coolant system in terms of main components (so everything other than any of the little hoses near the manifold) has been replaced with Genuine BMW parts. The S54 radiator is shorter and possibly a tad bit thicker.

    I am considering the thermostat which is a real bummer. I might go ahead and grab a high flow water pump while I am in there as well. Any reason to grab a low temp fan switch or low temp thermostat or just call it a day with an oem 88 degree thermostat?
    FYI: I installed a Stewart water pump when I was trying to replace the engine fan with an electric fan (I gave up and re-installed the engine fan), and it made no significant difference. It's nice to know it's in there, but not worth $175 (or whatever they cost now) I agree with previous post: don't go to low temp switch or tstat. You want the tstat controlling the water temp, so it should be close to normal operating temps.

  16. #16
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    So at idle yesterday (99 degrees) I was hitting 210. It would somewhat quickly drop back down to 205 or so as soon as I started moving but stop and go traffic didn’t help.

    Here in Nebraska we don’t have emissions so a low temp Thermostat should t be a problem however, with our cold winters it the car would probably run a bit cooler than I’d like. That being said I never drive the car on the winter and anymore so realistically wouldn’t be an issue.

    Good to know about the water pump. It sounds like the best upgrade would be to get a bigger radiator. Would the low temp fan switch help at all? Obviously won’t make a difference on the track but at idle I think it could.

    I’m going to try bleeding again tonight and let y’all know how that goes. Tough to test as it’s a pretty cool day today.

  17. #17
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    Absolutely no reason to get bigger rad, except for track maybe. Also agree no reason to change to cooler tstat of fan switch. These are all things you might do on a track car. Swap the tstat again, test it before it goes in, and I would suggest drilling a hole in the tstat top to help bleeding.

    When the temp spikes sitting, are both rad hoses hot? If not, it's likely your tstat. If they're both hot and super firm, it's probably something else. You could get a hydrocarbon tester ... maybe you're pushing combustion gas into the coolant heating it up (HG leak)
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  18. #18
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    This is my track car. I store over the winter, drive it maybe a couple weeks throughout the rest of the year and then to and from the track.

    The radiator inlet hose is hot and the radiator outlet is cool to the touch. I will say that neither hose feels super firm. I squeeze them during bleeding and I want to say they don’t require too much effort. So perhaps there is still air. How firm we talkin?

  19. #19
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    Quote Originally Posted by ewrjontan View Post
    This is my track car. I store over the winter, drive it maybe a couple weeks throughout the rest of the year and then to and from the track.

    The radiator inlet hose is hot and the radiator outlet is cool to the touch. I will say that neither hose feels super firm. I squeeze them during bleeding and I want to say they don’t require too much effort. So perhaps there is still air. How firm we talkin?
    Ahh, will if it's a track car, go wild

    Based on the fact there is a temp mismatch, I'm gonna say thermostat as well. Did the problems start after your swapped that, or did you have them before? How is it on track? Seems ok for a few laps, then temp spikes? After it sits overnight (like stone cold) you open the tank, is there any pressure?
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  20. #20
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    Wait so they should feel about the same temp? I figured the inlet (from the thermostat side) hose would feel hot, then the outlet should feel warm since the coolant has cooled down after passing through the radiator.

    Before my old radiator failed, I honestly can’t remember the temps. But I do remember I could do several laps before hitting close to 220 where I usually start to back off and do a cool down lap or two. I definitely did not find it to be a problem.

    After switching radiators I feel like I could only go maybe three laps before needing to cool down. It could be that I have also gotten faster (which I have) compared to when I first started.

    After sitting overnight, there is pressure upon opening the cap. When I tried to bleed with my vacuum tool (after I flushed my block and radiator last weekend) pressure held great so no leaks afaik.

  21. #21
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    Yeah, you got an issue ... if you can't do more than a few laps without hitting over 200. Should be able to run all day under 200, unless you're on someone's bumper. And because of the residual pressure, I'm revising my diagnosis to a HG leak. most likely at cyl 6, into the big coolant port at the back of the block.
    Last edited by ScotcH; 09-21-2022 at 09:28 PM.
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  22. #22
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    Oh, should there not be any pressure whatsoever? I can check tonight as the car has been sitting for over 24 hours at this point.

    Wouldn't I notice something with the coolant vacuum tool? Like it would not be able to hold -25 Hg under vacuum if there was any sort of leak whatsoever?

  23. #23
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    Quote Originally Posted by ewrjontan View Post
    Oh, should there not be any pressure whatsoever? I can check tonight as the car has been sitting for over 24 hours at this point.

    Wouldn't I notice something with the coolant vacuum tool? Like it would not be able to hold -25 Hg under vacuum if there was any sort of leak whatsoever?
    It should have zero pressure ... in fact it might have negative pressure if it's colder than when you last closed it. If the HG lean is small enough, you'll never see it when the car is cold. It opens up when it heats up, and of course under heavy load (ie, track). Typical symptoms, been there done that.
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  24. #24
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    Alright so I undid the coolant reservoir cap and didn’t seem to release any pressure. I’ll probably try bleeding again and also check for bubbling in the reservoir with the car on. Youve got me nervous now.

  25. #25
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    There is a cheap test for combustion gasses in the coolant. You can buy a do it yourself kit, or a shop will do it for about $30. It's probably more accurate than looking for bubbles.

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