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Temperature at idle

Discussion in '365 GT4 2+2/400/412' started by Schumi, Oct 11, 2021 at 8:34 AM.

  1. Schumi

    Schumi Formula Junior
    Silver Subscribed Owner

    Jun 5, 2002
    755
    Missouri
    Full Name:
    Daren
    What temperatures are you all seeing at idle after the engine is warmed up?

    My car runs at 86C or so down the road, but then pretty quickly goes over 90C on idle. It was always rock solid at 86C before the rebuild regardless of at-speed or idle.
     
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  3. raemin

    raemin Formula Junior

    Jan 16, 2007
    990
    Lyon (FR)
    Full Name:
    R. Emin
    During the last tests of my (failed) rebuild, the right cylinder head was at 85°C, whereas the left (faulty one) was at 95°C.

    You should point a laser gun to the cylinder heads. If there is a significant temperature difference you may have a problem in one bank? Perform the same on the exhausts. Check also for exhaust fume differences?

    If both banks are homogeneous, there are a few tricks you can implement in order to increase cooling :
    • place the Lucas cooling fans as close as possible to the condenser/radiator
    • use the proper coolant mix (see the 365 manual)
    • check that the felt rubber (? sorry for my bad english) that surrounds the yellow fan is still present as it significantly increase the suction
    • replace the infamous yellow fan by something that works...
    • add a bit more ignition timing (use with caution)
    • add a bit more fuel (either adjust CO or decrease K-Jet hot control pressure so as to make the meter more responsive under limited airflow)
    (that's applicable to the 400i as the 412 cooling is much improved)
     
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  4. Schumi

    Schumi Formula Junior
    Silver Subscribed Owner

    Jun 5, 2002
    755
    Missouri
    Full Name:
    Daren
    I've had a temp gun on it several times but never thought to compare the left and right head to each other.
     
  5. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,400
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    Schumi
    An idle temperature of 90 C is not a high number. The thermostat is he main controller of this temperature as long as all the fans are running. Do you have two or three fans? In either case be sure they are all running at eh 90 C condition. The fan thermostat can be changed easily. I put in one that comes on at a bit lower temp and does not shut off until down in the 60's. I don't think you have a big issue.
    Ken
     
  6. samsaprunoff

    samsaprunoff F1 Rookie
    Silver Subscribed

    Jun 8, 2004
    3,378
    Edmonton, AB Canada
    Full Name:
    Sam Saprunoff
    Good day Daren,

    Adding to what Ken said... Also confirm that your radiator fins are free of any debris, are not bent, and there is no obstruction in front of the radiator. The system cannot cool efficiently if air cannot go through the radiator. Lastly, when was the last time your radiator was cleaned and/or coolant changed. Over time as coolant ages a electro-chemical reaction can occur resulting in bits if crap floating around and plugging up various radiator passageways. Secondly, aging coolant looses its heat transfer efficiency. Thirdly, assuming all your fans are running, when was the last time they were internally cleaned/checked? I ask, as the fans internal bearings can become dry or gummed up, the carbon brushes can be nearing the end of their travel, and/or the motor's commutator can become oxidized. All of which will affect the fan's performance which will limit its efficiency to push/pull air through the radiator. I would check all of the above before looking deeper.

    Cheers,

    Sam
     
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  8. Schumi

    Schumi Formula Junior
    Silver Subscribed Owner

    Jun 5, 2002
    755
    Missouri
    Full Name:
    Daren
    Ken - Thanks for the response and I'll bet you are right. The fans do come on around 88C or so.
    Sam - I don't think the fans are bent or damaged in any way. There is no obstruction to the radiator other than the A/C condenser. The radiator was removed, cleaned and flushed (3x) and all new BMW coolant added. As for the fan motors, I haven't checked that.

    I am beginning to think the new A/C condenser is more restrictive than the old one as the fins seem very close when compared to the original.

    Thank you all for the comments as they are very helpful.
     
  9. raemin

    raemin Formula Junior

    Jan 16, 2007
    990
    Lyon (FR)
    Full Name:
    R. Emin
    If memory serves me well the thermostat fully opens at approx 80deg Celsius, and the fans are triggered at 83 (which is damn close). The fan temperature probe is on the bottom left of the radiator, while the dashboard temperature probe is on top of the engine valley. In other words when the measured temp on the valley is 90, the coolant has some time to cool below 83 degree before it reaches the bottomof the radiator.

    Also my dashboard probe was showing 90c when the laser gun was showing 85/95 (right/left bank).

    If I were in your shoes, as long as the temperature is homogeneous, I would not be afraid by your temperature readings.

    Also if you use some - 25/-35 coolant bear in mind that it is far less efficient than a - 5deg coolant. The lower the amount of antifreeze, the better.
     
  10. raemin

    raemin Formula Junior

    Jan 16, 2007
    990
    Lyon (FR)
    Full Name:
    R. Emin
    #8 raemin, Oct 14, 2021 at 8:12 AM
    Last edited: Oct 14, 2021 at 8:22 AM
    For the record i managed to shoehorn a bigger fan. I had the replace the oil hoses (longer ones) which allowed to place the radiator input/output on the right side of the car, hence clearing some space for a bigger fan (Mishimoto heavy duty with oldschool fan blades). If you don't mind departing from OEM, this works much better (and a bit more elegant than replacing the lucas by spal fans).
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  11. pattorpey

    pattorpey Rookie

    Oct 16, 2016
    10
    Dublin, Ireland
    Full Name:
    Pat Torpey
    Just my few cents worth.
    First, I would always suspect any vehicle instrumentation, unless it was calibrated. Too many things could affect the accuracy, such as supply voltage.
    Instead, I would look at how the instrument responds to change in operating conditions. The rapid increase in temperature from 86C while driving to over 90C when idling, as reported by Daren, is I believe of significance (irrespective of the actual numbers), and was something I also experienced on a Silver Shadow. It was so noticeable, and so rapid in onset, that the temperature increase would cause carburation problems (maybe due to fuel vapourisation) and cutting out, even while driving at low speeds after a moderately fast run. Initially I suspected a faulty viscous coupling on the fan drive.
    Eventually I traced it to clogged radiator fins. At some time in the past there must have been an oil leak, and the oil residue had lodged in the fins between the radiator and the A/C condenser, trapping loads of road dust and dirt and a museum full of dead insects. Cleaning both totally cured the problem.
    And by the way, the temp. gauge was simply graduated from C to N to H, with a nice fat "N" band in the middle!
     
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  13. Schumi

    Schumi Formula Junior
    Silver Subscribed Owner

    Jun 5, 2002
    755
    Missouri
    Full Name:
    Daren
    Thanks to Raemin and Pat for their suggestions/comments.
    Thing is about my car, it never heated up at any point ever before the full engine rebuild. The mechanic had some shop "fix" a very small leak on the radiator. I also wonder if during that repair if they didn't inadvertently clog a passage. I've used my temp gun on the radiator and I can't find any cold spots.

    What is most concerning, is that this rise in temps only occurs at idle, which makes me think it is likely an air-flow issue with the fans, the more dense looking A/C condenser, or slight clog in the radiator. The fans come on at the appropriate temp, and seem to blow just as hard as before the rebuild. The mechanic did nothing to them other than remove and replace. He has since provided them a better ground wire and replaced the relays on the fuse board. So I don't really think that is a strong candidate for the problem. The A/C condenser and the radiator however....
     
  14. raemin

    raemin Formula Junior

    Jan 16, 2007
    990
    Lyon (FR)
    Full Name:
    R. Emin
    Your modern BMW coolant is a more likely suspect. Just make a try with water & water wetter, if you see a dramatic increase you will know what's going on.

    On my other old rig, i just thin the coolant with 50% water (that's the maximum amount recommended by Motul). If I use pure coolant, in summer the engine knocks.

    By the way this is exactly what they recommend on bimmerworld when using the genuine BMW coolant. https://www.bimmerworld.com/Fluids/BMW-Coolant-Antifreeze/Genuine-BMW-Blue-Antifreeze.html
     
  15. Schumi

    Schumi Formula Junior
    Silver Subscribed Owner

    Jun 5, 2002
    755
    Missouri
    Full Name:
    Daren
    Raemin:
    The BMW coolant is, as I'm told by the mechanic, a 50/50 solution of coolant to water. I might try adding Water Wetter as I had pre-rebuild and see what happens.
     
  16. raemin

    raemin Formula Junior

    Jan 16, 2007
    990
    Lyon (FR)
    Full Name:
    R. Emin
    Water wetter alone will not increase the cooling efficiency, water wetter is a way to add more water and compensate for the missing additives.

    Assuming you do have the oldschool bmw blue formula (g48), you do have between 40% and 50% of antifreeze, which is ok for - 35deg celsius (-30F) that's three time the recomended concentration for - 5degC.

    Just have a look at the 366 manual and adjust your concentration as per the Ferrari antifreeze guidelines.

    By the way, the bmw blue coolant is a good idea on our cars, never fought about it, but well suited to our heads.
     

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